We measure the central kinematics for the dwarf spheroidal galaxy Leo I using integrated-light measurements and
previously published data. We find a steady rise in the velocity dispersion from 30000 into the center. The integratedlight kinematics provide a velocity dispersion of 11.76±0.66 km s−1
inside 7500. After applying appropriate corrections
to crowding in the central regions, we achieve consistent velocity dispersion values using velocities from individual stars.
Crowding corrections need to be applied when targeting individual stars in high density stellar environments. From
integrated light, we measure the surface brightness profile and find a shallow cusp towards the center. Axisymmetric,
orbit-based models measure the stellar mass-to-light ratio, black hole mass and parameters for a dark matter halo. At
large radii it is important to consider possible tidal effects from the Milky Way so we include a variety of assumptions
regarding the tidal radius. For every set of assumptions, models require a central black hole consistent with a mass
3.3 ± 2×106 M. The no-black-hole case for any of our assumptions is excluded at over 95% significance, with
6.4 < ∆χ
2 < 14. A black hole of this mass would have significant effect on dwarf galaxy formation and evolution.
The dark halo parameters are heavily affected by the assumptions for the tidal radii, with the circular velocity only
constrained to be above 30 km s−1
. Reasonable assumptions for the tidal radius result in stellar orbits consistent with
an isotropic distribution in the velocities. These more realistic models only show strong constraints for the mass of
the central black hole.
Kinematics and simulations_of_the_stellar_stream_in_the_halo_of_the_umbrella_...Sérgio Sacani
This document summarizes a study of the stellar stream and substructures around the Umbrella Galaxy (NGC 4651). Deep imaging and spectroscopy were used to characterize the properties and kinematics of the stream. Tracer objects like globular clusters and planetary nebulae were identified and found to delineate a kinematically cold feature in position-velocity space. Dynamical modeling suggests the stream originated from the tidal disruption of a dwarf galaxy on a highly eccentric orbit about 6-10 billion years ago. This work demonstrates the feasibility of using discrete tracers to recover the kinematics and model the dynamics of low surface brightness stellar streams around distant galaxies.
This document examines whether galaxy environments and the color-density relation can be robustly measured using photometric redshift (photo-z) surveys. It finds that:
1) Using optimized parameters for density measurements, a correlation between 2D projected density measurements from photo-z surveys and true 3D density can still be revealed, even with photo-z uncertainties up to 0.06.
2) The color-density relation remains visible in photo-z surveys out to z=0.8, despite photo-z uncertainties of 0.02-0.06.
3) A deep (i=25 magnitude) photo-z survey with photo-z uncertainties of 0.02 can measure small-scale galaxy
The behaviour of_dark_matter_associated_with_4_bright_cluster_galaxies_in_the...Sérgio Sacani
The document presents new Hubble Space Telescope imaging and Very Large Telescope integral-field spectroscopy of galaxy cluster Abell 3827. It finds that each of the four central galaxies in the cluster's 10 kpc core retains an associated massive dark matter halo. At least one galaxy is offset from its dark matter halo, with an offset of 1.62+0.50−0.47 kpc, within the uncertainties of mass modeling and statistical errors. If interpreted as evidence for self-interacting dark matter, this offset implies a dark matter self-interaction cross-section of (1.7 ± 0.7)×10−4 cm2/g.
This document describes the Sloan Low-mass Wide Pairs of Kinematically Equivalent Stars (SLoWPoKES) catalog, which contains 1342 very wide (projected separation >500 AU), low-mass (at least one mid-K to mid-M dwarf component) common proper motion pairs identified from the Sloan Digital Sky Survey. The catalog was constructed using astrometry, photometry, and proper motions to identify pairs with a probability of chance alignment ≤0.05. The catalog is intended to be a resource for detailed study of low-mass binary star systems and preliminary results describe the properties and characteristics of the wide, low-mass pairs.
MUSE sneaks a peek at extreme ram-pressure stripping events. I. A kinematic s...Sérgio Sacani
- MUSE observations of the galaxy ESO137-001 reveal an extended gaseous tail over 30 kpc long traced by H-alpha emission, providing evidence of an extreme ram pressure stripping event as the galaxy falls into the massive Norma galaxy cluster.
- Analysis of the H-alpha kinematics and stellar velocity field show that ram pressure has removed the interstellar medium from the outer disk while the primary tail is still fed by gas from the galaxy center, with gravitational interactions not appearing to be the main mechanism of gas removal.
- The stripped gas retains evidence of the disk's rotational velocity out to around 20 kpc downstream, indicating the galaxy is moving radially along the plane of the sky, while
This document describes observations of the galaxy ESO137-001 using the MUSE instrument on the VLT. The key points are:
1) MUSE observations reveal an extended gas tail stretching over 30 kpc from the galaxy, tracing ongoing ram pressure stripping as it falls into the Norma galaxy cluster.
2) Analysis of the gas kinematics and stellar velocity field show that ram pressure has removed the interstellar medium from the outer disk while the primary tail is still fed by gas from the galaxy center.
3) The stripped gas retains evidence of the disk's rotational velocity out to 20 kpc downstream, indicating the galaxy is moving radially through the cluster. Beyond this the gas shows greater turbulence,
This document summarizes observations of the lensed galaxy HATLAS J142935.3-002836 (H1429-0028) from the Herschel-ATLAS survey. Optical spectroscopy revealed the foreground lens is at redshift 0.218, while the background galaxy is at redshift 1.027. High-resolution imaging from Hubble Space Telescope and Keck adaptive optics show the background galaxy is comprised of two components and a tidal tail, resembling a major merger. Analysis of ALMA observations of CO emission provides a dynamical mass estimate of one component as 5.8 ± 1.7 × 1010 M☉. Modeling of the spectral energy distribution indicates the total stellar mass is 1.32
HST imaging of star-forming clumps in 6 GASP ram-pressure stripped galaxiesSérgio Sacani
Exploiting broad- and narrow-band images of the Hubble Space Telescope from near-UV to I-band
restframe, we study the star-forming clumps of six galaxies of the GASP sample undergoing strong
ram-pressure stripping (RPS). Clumps are detected in Hα and near-UV, tracing star formation on
different timescales. We consider clumps located in galaxy disks, in the stripped tails and those
formed in stripped gas but still close to the disk, called extraplanar. We detect 2406 Hα-selected
clumps (1708 in disks, 375 in extraplanar regions, and 323 in tails) and 3750 UV-selected clumps (2026
disk clumps, 825 extraplanar clumps and 899 tail clumps). Only ∼ 15% of star-forming clumps are
spatially resolved, meaning that most are smaller than ∼ 140 pc. We study the luminosity and size
distribution functions (LDFs and SDFs, respectively) and the luminosity-size relation. The average
LDF slope is 1.79 ± 0.09, while the average SDF slope is 3.1 ± 0.5. Results suggest the star formation
to be turbulence driven and scale-free, as in main-sequence galaxies. All the clumps, whether they are
in the disks or in the tails, have an enhanced Hα luminosity at a given size, compared to the clumps in
main-sequence galaxies. Indeed, their Hα luminosity is closer to that of clumps in starburst galaxies,
indicating that ram pressure is able to enhance the luminosity. No striking differences are found among
disk and tail clumps, suggesting that the different environments in which they are embedded play a
minor role in influencing the star formation.
Kinematics and simulations_of_the_stellar_stream_in_the_halo_of_the_umbrella_...Sérgio Sacani
This document summarizes a study of the stellar stream and substructures around the Umbrella Galaxy (NGC 4651). Deep imaging and spectroscopy were used to characterize the properties and kinematics of the stream. Tracer objects like globular clusters and planetary nebulae were identified and found to delineate a kinematically cold feature in position-velocity space. Dynamical modeling suggests the stream originated from the tidal disruption of a dwarf galaxy on a highly eccentric orbit about 6-10 billion years ago. This work demonstrates the feasibility of using discrete tracers to recover the kinematics and model the dynamics of low surface brightness stellar streams around distant galaxies.
This document examines whether galaxy environments and the color-density relation can be robustly measured using photometric redshift (photo-z) surveys. It finds that:
1) Using optimized parameters for density measurements, a correlation between 2D projected density measurements from photo-z surveys and true 3D density can still be revealed, even with photo-z uncertainties up to 0.06.
2) The color-density relation remains visible in photo-z surveys out to z=0.8, despite photo-z uncertainties of 0.02-0.06.
3) A deep (i=25 magnitude) photo-z survey with photo-z uncertainties of 0.02 can measure small-scale galaxy
The behaviour of_dark_matter_associated_with_4_bright_cluster_galaxies_in_the...Sérgio Sacani
The document presents new Hubble Space Telescope imaging and Very Large Telescope integral-field spectroscopy of galaxy cluster Abell 3827. It finds that each of the four central galaxies in the cluster's 10 kpc core retains an associated massive dark matter halo. At least one galaxy is offset from its dark matter halo, with an offset of 1.62+0.50−0.47 kpc, within the uncertainties of mass modeling and statistical errors. If interpreted as evidence for self-interacting dark matter, this offset implies a dark matter self-interaction cross-section of (1.7 ± 0.7)×10−4 cm2/g.
This document describes the Sloan Low-mass Wide Pairs of Kinematically Equivalent Stars (SLoWPoKES) catalog, which contains 1342 very wide (projected separation >500 AU), low-mass (at least one mid-K to mid-M dwarf component) common proper motion pairs identified from the Sloan Digital Sky Survey. The catalog was constructed using astrometry, photometry, and proper motions to identify pairs with a probability of chance alignment ≤0.05. The catalog is intended to be a resource for detailed study of low-mass binary star systems and preliminary results describe the properties and characteristics of the wide, low-mass pairs.
MUSE sneaks a peek at extreme ram-pressure stripping events. I. A kinematic s...Sérgio Sacani
- MUSE observations of the galaxy ESO137-001 reveal an extended gaseous tail over 30 kpc long traced by H-alpha emission, providing evidence of an extreme ram pressure stripping event as the galaxy falls into the massive Norma galaxy cluster.
- Analysis of the H-alpha kinematics and stellar velocity field show that ram pressure has removed the interstellar medium from the outer disk while the primary tail is still fed by gas from the galaxy center, with gravitational interactions not appearing to be the main mechanism of gas removal.
- The stripped gas retains evidence of the disk's rotational velocity out to around 20 kpc downstream, indicating the galaxy is moving radially along the plane of the sky, while
This document describes observations of the galaxy ESO137-001 using the MUSE instrument on the VLT. The key points are:
1) MUSE observations reveal an extended gas tail stretching over 30 kpc from the galaxy, tracing ongoing ram pressure stripping as it falls into the Norma galaxy cluster.
2) Analysis of the gas kinematics and stellar velocity field show that ram pressure has removed the interstellar medium from the outer disk while the primary tail is still fed by gas from the galaxy center.
3) The stripped gas retains evidence of the disk's rotational velocity out to 20 kpc downstream, indicating the galaxy is moving radially through the cluster. Beyond this the gas shows greater turbulence,
This document summarizes observations of the lensed galaxy HATLAS J142935.3-002836 (H1429-0028) from the Herschel-ATLAS survey. Optical spectroscopy revealed the foreground lens is at redshift 0.218, while the background galaxy is at redshift 1.027. High-resolution imaging from Hubble Space Telescope and Keck adaptive optics show the background galaxy is comprised of two components and a tidal tail, resembling a major merger. Analysis of ALMA observations of CO emission provides a dynamical mass estimate of one component as 5.8 ± 1.7 × 1010 M☉. Modeling of the spectral energy distribution indicates the total stellar mass is 1.32
HST imaging of star-forming clumps in 6 GASP ram-pressure stripped galaxiesSérgio Sacani
Exploiting broad- and narrow-band images of the Hubble Space Telescope from near-UV to I-band
restframe, we study the star-forming clumps of six galaxies of the GASP sample undergoing strong
ram-pressure stripping (RPS). Clumps are detected in Hα and near-UV, tracing star formation on
different timescales. We consider clumps located in galaxy disks, in the stripped tails and those
formed in stripped gas but still close to the disk, called extraplanar. We detect 2406 Hα-selected
clumps (1708 in disks, 375 in extraplanar regions, and 323 in tails) and 3750 UV-selected clumps (2026
disk clumps, 825 extraplanar clumps and 899 tail clumps). Only ∼ 15% of star-forming clumps are
spatially resolved, meaning that most are smaller than ∼ 140 pc. We study the luminosity and size
distribution functions (LDFs and SDFs, respectively) and the luminosity-size relation. The average
LDF slope is 1.79 ± 0.09, while the average SDF slope is 3.1 ± 0.5. Results suggest the star formation
to be turbulence driven and scale-free, as in main-sequence galaxies. All the clumps, whether they are
in the disks or in the tails, have an enhanced Hα luminosity at a given size, compared to the clumps in
main-sequence galaxies. Indeed, their Hα luminosity is closer to that of clumps in starburst galaxies,
indicating that ram pressure is able to enhance the luminosity. No striking differences are found among
disk and tail clumps, suggesting that the different environments in which they are embedded play a
minor role in influencing the star formation.
HST imaging of star-forming clumps in 6 GASP ram-pressure stripped galaxiesSérgio Sacani
Exploiting broad- and narrow-band images of the Hubble Space Telescope from near-UV to I-band
restframe, we study the star-forming clumps of six galaxies of the GASP sample undergoing strong
ram-pressure stripping (RPS). Clumps are detected in Hα and near-UV, tracing star formation on
different timescales. We consider clumps located in galaxy disks, in the stripped tails and those
formed in stripped gas but still close to the disk, called extraplanar. We detect 2406 Hα-selected
clumps (1708 in disks, 375 in extraplanar regions, and 323 in tails) and 3750 UV-selected clumps (2026
disk clumps, 825 extraplanar clumps and 899 tail clumps). Only ∼ 15% of star-forming clumps are
spatially resolved, meaning that most are smaller than ∼ 140 pc. We study the luminosity and size
distribution functions (LDFs and SDFs, respectively) and the luminosity-size relation. The average
LDF slope is 1.79 ± 0.09, while the average SDF slope is 3.1 ± 0.5. Results suggest the star formation
to be turbulence driven and scale-free, as in main-sequence galaxies. All the clumps, whether they are
in the disks or in the tails, have an enhanced Hα luminosity at a given size, compared to the clumps in
main-sequence galaxies. Indeed, their Hα luminosity is closer to that of clumps in starburst galaxies,
indicating that ram pressure is able to enhance the luminosity. No striking differences are found among
disk and tail clumps, suggesting that the different environments in which they are embedded play a
minor role in influencing the star formation.
HST imaging of star-forming clumps in 6 GASP ram-pressure stripped galaxiesSérgio Sacani
Exploiting broad- and narrow-band images of the Hubble Space Telescope from near-UV to I-band
restframe, we study the star-forming clumps of six galaxies of the GASP sample undergoing strong
ram-pressure stripping (RPS). Clumps are detected in Hα and near-UV, tracing star formation on
different timescales. We consider clumps located in galaxy disks, in the stripped tails and those
formed in stripped gas but still close to the disk, called extraplanar. We detect 2406 Hα-selected
clumps (1708 in disks, 375 in extraplanar regions, and 323 in tails) and 3750 UV-selected clumps (2026
disk clumps, 825 extraplanar clumps and 899 tail clumps). Only ∼ 15% of star-forming clumps are
spatially resolved, meaning that most are smaller than ∼ 140 pc. We study the luminosity and size
distribution functions (LDFs and SDFs, respectively) and the luminosity-size relation. The average
LDF slope is 1.79 ± 0.09, while the average SDF slope is 3.1 ± 0.5. Results suggest the star formation
to be turbulence driven and scale-free, as in main-sequence galaxies. All the clumps, whether they are
in the disks or in the tails, have an enhanced Hα luminosity at a given size, compared to the clumps in
main-sequence galaxies. Indeed, their Hα luminosity is closer to that of clumps in starburst galaxies,
indicating that ram pressure is able to enhance the luminosity. No striking differences are found among
disk and tail clumps, suggesting that the different environments in which they are embedded play a
minor role in influencing the star formation.
A 3d extinction_map_of_the_northern_galactic_plane_based_on_iphas_photometrySérgio Sacani
This document presents a 3D extinction map of the Northern Galactic Plane derived using photometry from the IPHAS survey. The map was constructed using a hierarchical Bayesian method that simultaneously estimates the distance-extinction relationship and properties of ~38 million stars along each line of sight. The map has fine angular resolution of ~10 arcminutes and distance resolution of 100 pc out to a depth of 5 kpc. In addition to mean extinction, the method also measures differential extinction arising from the fractal structure of the interstellar medium. Both the extinction map and catalogue of stellar parameters are made publicly available.
The high mass_stelar_initial_mass_function_in_m31_clustersSérgio Sacani
Em uma pesquisa feita com o Telescópio Espacial Hubble da NASA, analisando imagens de 2753 jovens, aglomerados estelares azuis, na vizinha galáxia de Andrômeda, a M31, os astrônomos descobriram que a M31 e a nossa própria galáxia, possuem uma porcentagem similar de estrelas recém-nascidas, com base na massa estudada.
Identificando qual porcentagem de estrelas tem uma massa particular, dentro de um aglomerado, ou sua Função de Massa Inicial, IMF, os cientistas podem interpretar melhor a luz de galáxias distantes e entender a história de formação das estrelas no universo.
A intensa pesquisa, agrupou 414 mosaicos fotográficos feitos pelo Hubble da M31, uma colaboração única feita entre astrônomos, cientistas cidadãos, voluntários que forneceram uma ajuda valiosa em analisar a montanha de dados do Hubble.
“Dada a quantidade de imagens do Hubble, nosso estudo da IMF, não seria possível sem a ajuda dos cientistas cidadãos”, disse Daniel Weisz, da Universidade de Washington em Seatle. Weisz, é o principal autor do artigo que foi publicado no dia 20 de Junho no The Astrophysical Journal.
This document is a dissertation by Joakim Carlsen submitted in 2014/2015 for a Bsc(Honours) in Applied Physics. It investigates detecting massive galaxies at high redshift (z > 4) using photometric data from the Dark Energy Survey (DES). The dissertation aims to identify massive galaxy candidates at z > 4 based on their colors and fit their spectral energy distributions using photometric redshift modeling software. Several high redshift massive galaxy candidates were identified and their properties were analyzed, with the most promising candidates to be proposed for follow-up spectroscopy to confirm their redshifts.
This pilot survey used modest aperture telescopes to image 8 nearby spiral galaxies in order to search for stellar tidal streams. Ultra-deep imaging revealed 6 previously undetected extensive (up to 30 kpc) stellar structures likely from tidally disrupted satellites. A diversity of tidal feature morphologies was found, including great circle-like streams, remote shells, and jets emerging from disks. Simulations predict tidal debris should be common and match the observed variety, providing evidence minor mergers have shaped disk galaxies since z=1.
The network of filaments with embedded clusters surrounding voids, which has been seen in maps derived from
redshift surveys and reproduced in simulations, has been referred to as the cosmic web. A complementary
description is provided by considering the shear in the velocity field of galaxies. The eigenvalues of the shear
provide information regarding whether or not a region is collapsing in three dimensions, which is the condition for
a knot, expanding in three dimensions, which is the condition for a void, or in the intermediate condition of a
filament or sheet. The structures that are quantitatively defined by the eigenvalues can be approximated by isocontours
that provide a visual representation of the cosmic velocity (V) web. The current application is based on
radial peculiar velocities from the Cosmicflows-2 collection of distances. The three-dimensional velocity field is
constructed using the Wiener filter methodology in the linear approximation. Eigenvalues of the velocity shear are
calculated at each point on a grid. Here, knots and filaments are visualized across a local domain of
diameter ~0.1c
Third epoch magellanic_clouud_proper_motionsSérgio Sacani
The document analyzes proper motion data from the Hubble Space Telescope to study the three-dimensional rotation field of the Large Magellanic Cloud (LMC) galaxy. It finds that:
1) The proper motion data implies a stellar dynamical center that coincides with the HI dynamical center from previous studies.
2) Combining the proper motion and line-of-sight velocity data provides insights into the LMC's rotation curve, disk viewing angles, and circular rotation speed of 91.7 km/s outside the central region.
3) The data paint a consistent picture of LMC rotation and yield improved constraints on the galaxy's distance, mass profile, and orbital history around the Milky Way.
Discovery of rotational modulations in the planetary mass companion 2m1207b i...Sérgio Sacani
Rotational modulations of brown dwarfs have recently provided powerful constraints on the properties
of ultra-cool atmospheres, including longitudinal and vertical cloud structures and cloud evolution.
Furthermore, periodic light curves directly probe the rotational periods of ultra-cool objects. We
present here, for the first time, time-resolved high-precision photometric measurements of a planetarymass
companion, 2M1207b. We observed the binary system with HST/WFC3 in two bands and with
two spacecraft roll angles. Using point spread function-based photometry, we reach a nearly photonnoise
limited accuracy for both the primary and the secondary. While the primary is consistent with
a flat light curve, the secondary shows modulations that are clearly detected in the combined light
curve as well as in di↵erent subsets of the data. The amplitudes are 1.36% in the F125W and 0.78%
in the F160W filters, respectively. By fitting sine waves to the light curves, we find a consistent period
of 10.7+1.2
−0.6 hours and similar phases in both bands. The J- and H-band amplitude ratio of 2M1207b
is very similar to a field brown dwarf that has identical spectral type but di↵erent J-H color. Importantly,
our study also measures, for the first time, the rotation period for a directly imaged extra-solar
planetary-mass companion.
We present deep optical images of the Large and Small Magellanic Clouds (LMC and SMC) using
a low cost telephoto lens with a wide field of view to explore stellar substructure in the outskirts
of the stellar disk of the LMC (r < 10 degrees from the center). These data have higher resolution
than existing star count maps, and highlight the existence of stellar arcs and multiple spiral arms in
the northern periphery, with no comparable counterparts in the South. We compare these data to
detailed simulations of the LMC disk outskirts, following interactions with its low mass companion,
the SMC. We consider interaction in isolation and with the inclusion of the Milky Way tidal field.
The simulations are used to assess the origin of the northern structures, including also the low density
stellar arc recently identified in the DES data by Mackey et al. (2015) at ∼ 15 degrees. We conclude
that repeated close interactions with the SMC are primarily responsible for the asymmetric stellar
structures seen in the periphery of the LMC. The orientation and density of these arcs can be used to
constrain the LMC’s interaction history with and impact parameter of the SMC. More generally, we
find that such asymmetric structures should be ubiquitous about pairs of dwarfs and can persist for
1-2 Gyr even after the secondary merges entirely with the primary. As such, the lack of a companion
around a Magellanic Irregular does not disprove the hypothesis that their asymmetric structures are
driven by dwarf-dwarf interactions.
The document analyzes the merger fractions of radio-loud and radio-quiet active galactic nuclei (AGN) at z > 1 using new Hubble Space Telescope (HST) samples. It finds that 92% (+8%/-14%) of radio-loud galaxies at z > 1 show evidence of recent or ongoing mergers, while only 38% (+16%/-15%) of matched radio-quiet samples exhibit mergers. This provides strong evidence that mergers are the triggering mechanism for radio-loud AGN phenomena like relativistic jet launching, and that major black hole mergers may spin up central supermassive black holes in these objects.
Star formation at the smallest scales; A JWST study of the clump populations ...Sérgio Sacani
We present the clump populations detected in 18 lensed galaxies at redshifts 1 to 8.5 within the lensing cluster field SMACS0723.
The recent JWST Early Release Observations of this poorly known region of the sky have revealed numerous point-like sources
within and surrounding their host galaxies, undetected in the shallower HST images. We use JWST multiband photometry and
the lensing model of this galaxy cluster to estimate the intrinsic sizes and magnitudes of the stellar clumps. We derive optical
restframe effective radii from <10 to hundreds pc and masses ranging from ∼ 105
to 109 M, overlapping with massive star
clusters in the local universe. Clump ages range from 1 Myr to 1 Gyr. We compare the crossing time to the age of the clumps
and determine that between 45 and 60 % of the detected clumps are consistent with being gravitationally bound. On average,
the dearth of Gyr old clumps suggests that the dissolution time scales are shorter than 1 Gyr. We see a significant increase in the
luminosity (mass) surface density of the clumps with redshift. Clumps in reionisation era galaxies have stellar densities higher
than star clusters in the local universe. We zoom in into single galaxies at redshift < 6 and find for two galaxies, the Sparkler and
the Firework, that their star clusters/clumps show distinctive colour distributions and location surrounding their host galaxy that
are compatible with being accredited or formed during merger events. The ages of some of the compact clusters are between
1 and 4 Gyr, e.g., globular cluster precursors formed around 9-12 Gyr ago. Our study, conducted on a small sample of galaxies,
shows the potential of JWST observations for understanding the conditions under which star clusters form in rapidly evolving
galaxies.
A spectroscopic sample_of_massive_galaxiesSérgio Sacani
This document describes a study of 16 massive galaxies at z ~ 2 selected from the 3D-HST spectroscopic survey based on the detection of a strong 4000 Angstrom break in their spectra. Spectroscopy and imaging from HST/WFC3 are used to determine accurate redshifts, stellar population properties, and structural parameters. The sample significantly increases the number of spectroscopically confirmed evolved galaxies at z ~ 2 with robust size measurements. The analysis populates the mass-size relation and finds it is consistent with local relations but with smaller sizes by a factor of 2-3. A model is presented where the observed size evolution is explained by quenching of increasingly larger star-forming galaxies at a rate set by
A higher efficiency_of_converting_gas_to_stars_push_galaxies_at_z_1_6_well_ab...Sérgio Sacani
Galáxias formando estrelas em taxas extremas a nove bilhões de anos atrás eram mais eficientes do que a média das galáxias atuais, descobriram os pesquisadores.
A maioria das estrelas acredita-se localizam-se na sequência principal onde quanto maior a massa da galáxia, mais eficiente ela é na formação de novas estrelas. Contudo, de vez em quando uma galáxia apresentará uma explosão de novas estrelas que brilham mais do que o resto. Uma colisão entre duas grandes galáxias é normalmente a causa dessas fases de explosões de formação de estrelas, onde o gás frio que reside nas grandes nuvens moleculares torna-se o combustível para sustentar essas altas taxas de formação de estrelas.
A questão que os astrônomos têm feito é se essas explosões de estrelas no início o universo foram o resultado de se ter um suprimento de gás abundante, ou se as galáxias convertiam o gás de maneira mais eficiente.
Um novo estudo, publicado no Astrophysical Journal Letters de 15 de Outubro, liderado por John Silverman, do Kavli Institute for Physics and Mathematics of the Universe, estudou o conteúdo do gás monóxido de carbono (CO) em sete galáxias de explosão de estrelas muito distantes, quando o universo tinha apenas 4 bilhões de anos de vida. Isso foi possível devido a capacidade do Atacama Large Millimiter/Submillimiter Array (ALMA), localizado no platô no topo da montanha no Chile, que trabalha para detectar as ondas eletromagnéticas no comprimento de onda milimétrico (importante para se estudar o gás molecular) e um nível de sensibilidade que só agora começa a ser explorado pelos astrônomos.
Os pesquisadores descobriram que a quantidade de gás CO emitido já tinha diminuído, mesmo apesar da galáxia continuar a formar estrelas em altas taxas. Essas observações são similares àquelas registradas para as galáxias de explosões de estrelas próximas da Terra atualmente, mas a quantidade da depleção de gás não foi tão rápida quanto se esperava. Isso levou os pesquisadores a concluírem que poderia haver um contínuo aumento na eficiência, dependendo em de quanto acima da taxa de se formar estrelas ela está da sequência principal.
Small scatter and_nearly_isothermal_mass_profiles_to_four_half_light_radii_fr...Sérgio Sacani
This document summarizes the results of a study analyzing the total mass density profiles of 14 early-type galaxies using two-dimensional stellar kinematic data out to large radii of 2-6 half-light radii. The study finds that the total density profiles are well described by a nearly-isothermal power law with density proportional to radius from 0.1 to at least 4 half-light radii. The average logarithmic slope is -2.19 with a small scatter of only 0.11. This places tight constraints on galaxy formation models and illustrates the power of extended two-dimensional stellar kinematic observations.
ALMA Measurement of 10 kpc-scale Lensing Power Spectra towards the Lensed Qua...Sérgio Sacani
The lensing power spectra for gravitational potential, astrometric shift, and convergence perturbations are powerful probes to investigate dark matter structures on small
scales. We report the first lower and upper bounds of these lensing power spectra on
angular scale ∼ 1
′′ towards the anomalous quadruply lensed quasar MG J0414+0534
at a redshift z = 2.639. To obtain the spectra, we conducted observations of
MG J0414+0534 using the Atacama Large Millimeter/submillimeter Array (ALMA)
with high angular resolution (0.
′′02-0.
′′05). We developed a new partially non-parametric
method in which Fourier coefficients of potential perturbation are adjusted to minimize
the difference between linear combinations of weighted mean de-lensed images. Using
positions of radio jet components, extended dust emission on scales > 1 kpc, and midinfrared flux ratios, the range of measured convergence, astrometric shift, and potential
powers at an angular scale of ∼ 1.
′′1 (corresponding to an angular wave number of
l = 1.2 × 106 or ∼ 9 kpc in the primary lens plane) within 1 σ are ∆κ = 0.021 − 0.028,
∆α = 7 − 9 mas, and ∆ψ = 1.2 − 1.6 mas2
, respectively. Our result is consistent with
the predicted abundance of halos in the line of sight and subhalos in cold dark matter
models. Our partially non-parametric lens models suggest a presence of a clump in
the vicinity of object Y, a possible dusty dwarf galaxy and some small clumps in the
vicinity of other lensed quadruple images. Although much fainter than the previous
report, we detected weak continuum emission possibly from object Y with a peak flux
of ∼ 100 µJy beam−1
at the ∼ 4 σ level.
The green valley_is_a_red_herring_galaxy_zoo_reveals_two_evolutionary_pathwaysSérgio Sacani
This document summarizes research using data from Galaxy Zoo, SDSS, and GALEX to study how star formation is quenched in low-redshift galaxies. The key findings are:
1) Taking galaxy morphology into account, the "green valley" is not a single transitional state, as was previously thought.
2) Only a small population of blue early-type galaxies rapidly transition across the green valley as their morphology transforms from disk to spheroid and star formation is quenched quickly.
3) The majority of blue star-forming galaxies have significant disks and retain their late-type morphology as their star formation rates decline very slowly.
4) Different evolutionary pathways are observed for early- and late-type
This document introduces the VLT-FLAMES Tarantula Survey, which obtained multi-epoch optical spectroscopy of over 800 massive stars in the 30 Doradus region of the Large Magellanic Cloud. The survey aims to detect massive binary systems through variations in radial velocities and to characterize the properties of O- and B-type stars, addressing questions about stellar and cluster evolution. Spectral classifications are provided for newly discovered emission-line stars, including a new Wolf-Rayet star. The survey data and reduction procedures are overviewed, and upcoming analyses of the massive star properties are announced.
UV and Hα HST observations of 6 GASP jellyfish galaxiesSérgio Sacani
Star-forming, Hα-emitting clumps are found embedded in the gaseous tails of galaxies undergoing
intense ram pressure stripping in galaxy clusters, so-called jellyfish galaxies. These clumps offer a
unique opportunity to study star formation under extreme conditions, in the absence of an underlying
disk and embedded within the hot intracluster medium. Yet, a comprehensive, high spatial resolution
study of these systems is missing. We obtained UVIS/HST data to observe the first statistical sample
of clumps in the tails and disks of six jellyfish galaxies from the GASP survey; we used a combination
of broad-band (UV to I) filters and a narrow-band Hα filter. HST observations are needed to study
the sizes, stellar masses and ages of the clumps and their clustering hierarchy. These observations will
be used to study the clump scaling relations, the universality of the star formation process and verify
whether a disk is irrelevant, as hinted by jellyfish galaxy results. This paper presents the observations,
data reduction strategy, and some general results based on the preliminary data analysis. The UVIS
high spatial resolution gives an unprecedented sharp view of the complex structure of the inner regions
of the galaxies and of the substructures in the galaxy disks. We found clear signatures of stripping
in regions very close in projection to the galactic disk. The star-forming regions in the stripped tails
are extremely bright and compact while we did not detect a significant number of star-forming clumps
outside those detected by MUSE. The paper finally presents the development plan for the project.
UV and Hα HST observations of 6 GASP jellyfish galaxiesSérgio Sacani
Star-forming, Hα-emitting clumps are found embedded in the gaseous tails of galaxies undergoing
intense ram pressure stripping in galaxy clusters, so-called jellyfish galaxies. These clumps offer a
unique opportunity to study star formation under extreme conditions, in the absence of an underlying
disk and embedded within the hot intracluster medium. Yet, a comprehensive, high spatial resolution
study of these systems is missing. We obtained UVIS/HST data to observe the first statistical sample
of clumps in the tails and disks of six jellyfish galaxies from the GASP survey; we used a combination
of broad-band (UV to I) filters and a narrow-band Hα filter. HST observations are needed to study
the sizes, stellar masses and ages of the clumps and their clustering hierarchy. These observations will
be used to study the clump scaling relations, the universality of the star formation process and verify
whether a disk is irrelevant, as hinted by jellyfish galaxy results. This paper presents the observations,
data reduction strategy, and some general results based on the preliminary data analysis. The UVIS
high spatial resolution gives an unprecedented sharp view of the complex structure of the inner regions
of the galaxies and of the substructures in the galaxy disks. We found clear signatures of stripping
in regions very close in projection to the galactic disk. The star-forming regions in the stripped tails
are extremely bright and compact while we did not detect a significant number of star-forming clumps
outside those detected by MUSE. The paper finally presents the development plan for the project.
Discovery of An Apparent Red, High-Velocity Type Ia Supernova at 𝐳 = 2.9 wi...Sérgio Sacani
We present the JWST discovery of SN 2023adsy, a transient object located in a host galaxy JADES-GS
+
53.13485
−
27.82088
with a host spectroscopic redshift of
2.903
±
0.007
. The transient was identified in deep James Webb Space Telescope (JWST)/NIRCam imaging from the JWST Advanced Deep Extragalactic Survey (JADES) program. Photometric and spectroscopic followup with NIRCam and NIRSpec, respectively, confirm the redshift and yield UV-NIR light-curve, NIR color, and spectroscopic information all consistent with a Type Ia classification. Despite its classification as a likely SN Ia, SN 2023adsy is both fairly red (
�
(
�
−
�
)
∼
0.9
) despite a host galaxy with low-extinction and has a high Ca II velocity (
19
,
000
±
2
,
000
km/s) compared to the general population of SNe Ia. While these characteristics are consistent with some Ca-rich SNe Ia, particularly SN 2016hnk, SN 2023adsy is intrinsically brighter than the low-
�
Ca-rich population. Although such an object is too red for any low-
�
cosmological sample, we apply a fiducial standardization approach to SN 2023adsy and find that the SN 2023adsy luminosity distance measurement is in excellent agreement (
≲
1
�
) with
Λ
CDM. Therefore unlike low-
�
Ca-rich SNe Ia, SN 2023adsy is standardizable and gives no indication that SN Ia standardized luminosities change significantly with redshift. A larger sample of distant SNe Ia is required to determine if SN Ia population characteristics at high-
�
truly diverge from their low-
�
counterparts, and to confirm that standardized luminosities nevertheless remain constant with redshift.
Evidence of Jet Activity from the Secondary Black Hole in the OJ 287 Binary S...Sérgio Sacani
Wereport the study of a huge optical intraday flare on 2021 November 12 at 2 a.m. UT in the blazar OJ287. In the binary black hole model, it is associated with an impact of the secondary black hole on the accretion disk of the primary. Our multifrequency observing campaign was set up to search for such a signature of the impact based on a prediction made 8 yr earlier. The first I-band results of the flare have already been reported by Kishore et al. (2024). Here we combine these data with our monitoring in the R-band. There is a big change in the R–I spectral index by 1.0 ±0.1 between the normal background and the flare, suggesting a new component of radiation. The polarization variation during the rise of the flare suggests the same. The limits on the source size place it most reasonably in the jet of the secondary BH. We then ask why we have not seen this phenomenon before. We show that OJ287 was never before observed with sufficient sensitivity on the night when the flare should have happened according to the binary model. We also study the probability that this flare is just an oversized example of intraday variability using the Krakow data set of intense monitoring between 2015 and 2023. We find that the occurrence of a flare of this size and rapidity is unlikely. In machine-readable Tables 1 and 2, we give the full orbit-linked historical light curve of OJ287 as well as the dense monitoring sample of Krakow.
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Exploiting broad- and narrow-band images of the Hubble Space Telescope from near-UV to I-band
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ram-pressure stripping (RPS). Clumps are detected in Hα and near-UV, tracing star formation on
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HST imaging of star-forming clumps in 6 GASP ram-pressure stripped galaxiesSérgio Sacani
Exploiting broad- and narrow-band images of the Hubble Space Telescope from near-UV to I-band
restframe, we study the star-forming clumps of six galaxies of the GASP sample undergoing strong
ram-pressure stripping (RPS). Clumps are detected in Hα and near-UV, tracing star formation on
different timescales. We consider clumps located in galaxy disks, in the stripped tails and those
formed in stripped gas but still close to the disk, called extraplanar. We detect 2406 Hα-selected
clumps (1708 in disks, 375 in extraplanar regions, and 323 in tails) and 3750 UV-selected clumps (2026
disk clumps, 825 extraplanar clumps and 899 tail clumps). Only ∼ 15% of star-forming clumps are
spatially resolved, meaning that most are smaller than ∼ 140 pc. We study the luminosity and size
distribution functions (LDFs and SDFs, respectively) and the luminosity-size relation. The average
LDF slope is 1.79 ± 0.09, while the average SDF slope is 3.1 ± 0.5. Results suggest the star formation
to be turbulence driven and scale-free, as in main-sequence galaxies. All the clumps, whether they are
in the disks or in the tails, have an enhanced Hα luminosity at a given size, compared to the clumps in
main-sequence galaxies. Indeed, their Hα luminosity is closer to that of clumps in starburst galaxies,
indicating that ram pressure is able to enhance the luminosity. No striking differences are found among
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Rotational modulations of brown dwarfs have recently provided powerful constraints on the properties
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Furthermore, periodic light curves directly probe the rotational periods of ultra-cool objects. We
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in the F160W filters, respectively. By fitting sine waves to the light curves, we find a consistent period
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our study also measures, for the first time, the rotation period for a directly imaged extra-solar
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to 109 M, overlapping with massive star
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than star clusters in the local universe. We zoom in into single galaxies at redshift < 6 and find for two galaxies, the Sparkler and
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are compatible with being accredited or formed during merger events. The ages of some of the compact clusters are between
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A questão que os astrônomos têm feito é se essas explosões de estrelas no início o universo foram o resultado de se ter um suprimento de gás abundante, ou se as galáxias convertiam o gás de maneira mais eficiente.
Um novo estudo, publicado no Astrophysical Journal Letters de 15 de Outubro, liderado por John Silverman, do Kavli Institute for Physics and Mathematics of the Universe, estudou o conteúdo do gás monóxido de carbono (CO) em sete galáxias de explosão de estrelas muito distantes, quando o universo tinha apenas 4 bilhões de anos de vida. Isso foi possível devido a capacidade do Atacama Large Millimiter/Submillimiter Array (ALMA), localizado no platô no topo da montanha no Chile, que trabalha para detectar as ondas eletromagnéticas no comprimento de onda milimétrico (importante para se estudar o gás molecular) e um nível de sensibilidade que só agora começa a ser explorado pelos astrônomos.
Os pesquisadores descobriram que a quantidade de gás CO emitido já tinha diminuído, mesmo apesar da galáxia continuar a formar estrelas em altas taxas. Essas observações são similares àquelas registradas para as galáxias de explosões de estrelas próximas da Terra atualmente, mas a quantidade da depleção de gás não foi tão rápida quanto se esperava. Isso levou os pesquisadores a concluírem que poderia haver um contínuo aumento na eficiência, dependendo em de quanto acima da taxa de se formar estrelas ela está da sequência principal.
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ALMA Measurement of 10 kpc-scale Lensing Power Spectra towards the Lensed Qua...Sérgio Sacani
The lensing power spectra for gravitational potential, astrometric shift, and convergence perturbations are powerful probes to investigate dark matter structures on small
scales. We report the first lower and upper bounds of these lensing power spectra on
angular scale ∼ 1
′′ towards the anomalous quadruply lensed quasar MG J0414+0534
at a redshift z = 2.639. To obtain the spectra, we conducted observations of
MG J0414+0534 using the Atacama Large Millimeter/submillimeter Array (ALMA)
with high angular resolution (0.
′′02-0.
′′05). We developed a new partially non-parametric
method in which Fourier coefficients of potential perturbation are adjusted to minimize
the difference between linear combinations of weighted mean de-lensed images. Using
positions of radio jet components, extended dust emission on scales > 1 kpc, and midinfrared flux ratios, the range of measured convergence, astrometric shift, and potential
powers at an angular scale of ∼ 1.
′′1 (corresponding to an angular wave number of
l = 1.2 × 106 or ∼ 9 kpc in the primary lens plane) within 1 σ are ∆κ = 0.021 − 0.028,
∆α = 7 − 9 mas, and ∆ψ = 1.2 − 1.6 mas2
, respectively. Our result is consistent with
the predicted abundance of halos in the line of sight and subhalos in cold dark matter
models. Our partially non-parametric lens models suggest a presence of a clump in
the vicinity of object Y, a possible dusty dwarf galaxy and some small clumps in the
vicinity of other lensed quadruple images. Although much fainter than the previous
report, we detected weak continuum emission possibly from object Y with a peak flux
of ∼ 100 µJy beam−1
at the ∼ 4 σ level.
The green valley_is_a_red_herring_galaxy_zoo_reveals_two_evolutionary_pathwaysSérgio Sacani
This document summarizes research using data from Galaxy Zoo, SDSS, and GALEX to study how star formation is quenched in low-redshift galaxies. The key findings are:
1) Taking galaxy morphology into account, the "green valley" is not a single transitional state, as was previously thought.
2) Only a small population of blue early-type galaxies rapidly transition across the green valley as their morphology transforms from disk to spheroid and star formation is quenched quickly.
3) The majority of blue star-forming galaxies have significant disks and retain their late-type morphology as their star formation rates decline very slowly.
4) Different evolutionary pathways are observed for early- and late-type
This document introduces the VLT-FLAMES Tarantula Survey, which obtained multi-epoch optical spectroscopy of over 800 massive stars in the 30 Doradus region of the Large Magellanic Cloud. The survey aims to detect massive binary systems through variations in radial velocities and to characterize the properties of O- and B-type stars, addressing questions about stellar and cluster evolution. Spectral classifications are provided for newly discovered emission-line stars, including a new Wolf-Rayet star. The survey data and reduction procedures are overviewed, and upcoming analyses of the massive star properties are announced.
UV and Hα HST observations of 6 GASP jellyfish galaxiesSérgio Sacani
Star-forming, Hα-emitting clumps are found embedded in the gaseous tails of galaxies undergoing
intense ram pressure stripping in galaxy clusters, so-called jellyfish galaxies. These clumps offer a
unique opportunity to study star formation under extreme conditions, in the absence of an underlying
disk and embedded within the hot intracluster medium. Yet, a comprehensive, high spatial resolution
study of these systems is missing. We obtained UVIS/HST data to observe the first statistical sample
of clumps in the tails and disks of six jellyfish galaxies from the GASP survey; we used a combination
of broad-band (UV to I) filters and a narrow-band Hα filter. HST observations are needed to study
the sizes, stellar masses and ages of the clumps and their clustering hierarchy. These observations will
be used to study the clump scaling relations, the universality of the star formation process and verify
whether a disk is irrelevant, as hinted by jellyfish galaxy results. This paper presents the observations,
data reduction strategy, and some general results based on the preliminary data analysis. The UVIS
high spatial resolution gives an unprecedented sharp view of the complex structure of the inner regions
of the galaxies and of the substructures in the galaxy disks. We found clear signatures of stripping
in regions very close in projection to the galactic disk. The star-forming regions in the stripped tails
are extremely bright and compact while we did not detect a significant number of star-forming clumps
outside those detected by MUSE. The paper finally presents the development plan for the project.
UV and Hα HST observations of 6 GASP jellyfish galaxiesSérgio Sacani
Star-forming, Hα-emitting clumps are found embedded in the gaseous tails of galaxies undergoing
intense ram pressure stripping in galaxy clusters, so-called jellyfish galaxies. These clumps offer a
unique opportunity to study star formation under extreme conditions, in the absence of an underlying
disk and embedded within the hot intracluster medium. Yet, a comprehensive, high spatial resolution
study of these systems is missing. We obtained UVIS/HST data to observe the first statistical sample
of clumps in the tails and disks of six jellyfish galaxies from the GASP survey; we used a combination
of broad-band (UV to I) filters and a narrow-band Hα filter. HST observations are needed to study
the sizes, stellar masses and ages of the clumps and their clustering hierarchy. These observations will
be used to study the clump scaling relations, the universality of the star formation process and verify
whether a disk is irrelevant, as hinted by jellyfish galaxy results. This paper presents the observations,
data reduction strategy, and some general results based on the preliminary data analysis. The UVIS
high spatial resolution gives an unprecedented sharp view of the complex structure of the inner regions
of the galaxies and of the substructures in the galaxy disks. We found clear signatures of stripping
in regions very close in projection to the galactic disk. The star-forming regions in the stripped tails
are extremely bright and compact while we did not detect a significant number of star-forming clumps
outside those detected by MUSE. The paper finally presents the development plan for the project.
Similar to DYNAMICAL ANALYSIS OF THE DARK MATTER AND CENTRAL BLACK HOLE MASS IN THE DWARF SPHEROIDAL LEO I (20)
Discovery of An Apparent Red, High-Velocity Type Ia Supernova at 𝐳 = 2.9 wi...Sérgio Sacani
We present the JWST discovery of SN 2023adsy, a transient object located in a host galaxy JADES-GS
+
53.13485
−
27.82088
with a host spectroscopic redshift of
2.903
±
0.007
. The transient was identified in deep James Webb Space Telescope (JWST)/NIRCam imaging from the JWST Advanced Deep Extragalactic Survey (JADES) program. Photometric and spectroscopic followup with NIRCam and NIRSpec, respectively, confirm the redshift and yield UV-NIR light-curve, NIR color, and spectroscopic information all consistent with a Type Ia classification. Despite its classification as a likely SN Ia, SN 2023adsy is both fairly red (
�
(
�
−
�
)
∼
0.9
) despite a host galaxy with low-extinction and has a high Ca II velocity (
19
,
000
±
2
,
000
km/s) compared to the general population of SNe Ia. While these characteristics are consistent with some Ca-rich SNe Ia, particularly SN 2016hnk, SN 2023adsy is intrinsically brighter than the low-
�
Ca-rich population. Although such an object is too red for any low-
�
cosmological sample, we apply a fiducial standardization approach to SN 2023adsy and find that the SN 2023adsy luminosity distance measurement is in excellent agreement (
≲
1
�
) with
Λ
CDM. Therefore unlike low-
�
Ca-rich SNe Ia, SN 2023adsy is standardizable and gives no indication that SN Ia standardized luminosities change significantly with redshift. A larger sample of distant SNe Ia is required to determine if SN Ia population characteristics at high-
�
truly diverge from their low-
�
counterparts, and to confirm that standardized luminosities nevertheless remain constant with redshift.
Evidence of Jet Activity from the Secondary Black Hole in the OJ 287 Binary S...Sérgio Sacani
Wereport the study of a huge optical intraday flare on 2021 November 12 at 2 a.m. UT in the blazar OJ287. In the binary black hole model, it is associated with an impact of the secondary black hole on the accretion disk of the primary. Our multifrequency observing campaign was set up to search for such a signature of the impact based on a prediction made 8 yr earlier. The first I-band results of the flare have already been reported by Kishore et al. (2024). Here we combine these data with our monitoring in the R-band. There is a big change in the R–I spectral index by 1.0 ±0.1 between the normal background and the flare, suggesting a new component of radiation. The polarization variation during the rise of the flare suggests the same. The limits on the source size place it most reasonably in the jet of the secondary BH. We then ask why we have not seen this phenomenon before. We show that OJ287 was never before observed with sufficient sensitivity on the night when the flare should have happened according to the binary model. We also study the probability that this flare is just an oversized example of intraday variability using the Krakow data set of intense monitoring between 2015 and 2023. We find that the occurrence of a flare of this size and rapidity is unlikely. In machine-readable Tables 1 and 2, we give the full orbit-linked historical light curve of OJ287 as well as the dense monitoring sample of Krakow.
Candidate young stellar objects in the S-cluster: Kinematic analysis of a sub...Sérgio Sacani
Context. The observation of several L-band emission sources in the S cluster has led to a rich discussion of their nature. However, a definitive answer to the classification of the dusty objects requires an explanation for the detection of compact Doppler-shifted Brγ emission. The ionized hydrogen in combination with the observation of mid-infrared L-band continuum emission suggests that most of these sources are embedded in a dusty envelope. These embedded sources are part of the S-cluster, and their relationship to the S-stars is still under debate. To date, the question of the origin of these two populations has been vague, although all explanations favor migration processes for the individual cluster members. Aims. This work revisits the S-cluster and its dusty members orbiting the supermassive black hole SgrA* on bound Keplerian orbits from a kinematic perspective. The aim is to explore the Keplerian parameters for patterns that might imply a nonrandom distribution of the sample. Additionally, various analytical aspects are considered to address the nature of the dusty sources. Methods. Based on the photometric analysis, we estimated the individual H−K and K−L colors for the source sample and compared the results to known cluster members. The classification revealed a noticeable contrast between the S-stars and the dusty sources. To fit the flux-density distribution, we utilized the radiative transfer code HYPERION and implemented a young stellar object Class I model. We obtained the position angle from the Keplerian fit results; additionally, we analyzed the distribution of the inclinations and the longitudes of the ascending node. Results. The colors of the dusty sources suggest a stellar nature consistent with the spectral energy distribution in the near and midinfrared domains. Furthermore, the evaporation timescales of dusty and gaseous clumps in the vicinity of SgrA* are much shorter ( 2yr) than the epochs covered by the observations (≈15yr). In addition to the strong evidence for the stellar classification of the D-sources, we also find a clear disk-like pattern following the arrangements of S-stars proposed in the literature. Furthermore, we find a global intrinsic inclination for all dusty sources of 60 ± 20◦, implying a common formation process. Conclusions. The pattern of the dusty sources manifested in the distribution of the position angles, inclinations, and longitudes of the ascending node strongly suggests two different scenarios: the main-sequence stars and the dusty stellar S-cluster sources share a common formation history or migrated with a similar formation channel in the vicinity of SgrA*. Alternatively, the gravitational influence of SgrA* in combination with a massive perturber, such as a putative intermediate mass black hole in the IRS 13 cluster, forces the dusty objects and S-stars to follow a particular orbital arrangement. Key words. stars: black holes– stars: formation– Galaxy: center– galaxies: star formation
JAMES WEBB STUDY THE MASSIVE BLACK HOLE SEEDSSérgio Sacani
The pathway(s) to seeding the massive black holes (MBHs) that exist at the heart of galaxies in the present and distant Universe remains an unsolved problem. Here we categorise, describe and quantitatively discuss the formation pathways of both light and heavy seeds. We emphasise that the most recent computational models suggest that rather than a bimodal-like mass spectrum between light and heavy seeds with light at one end and heavy at the other that instead a continuum exists. Light seeds being more ubiquitous and the heavier seeds becoming less and less abundant due the rarer environmental conditions required for their formation. We therefore examine the different mechanisms that give rise to different seed mass spectrums. We show how and why the mechanisms that produce the heaviest seeds are also among the rarest events in the Universe and are hence extremely unlikely to be the seeds for the vast majority of the MBH population. We quantify, within the limits of the current large uncertainties in the seeding processes, the expected number densities of the seed mass spectrum. We argue that light seeds must be at least 103 to 105 times more numerous than heavy seeds to explain the MBH population as a whole. Based on our current understanding of the seed population this makes heavy seeds (Mseed > 103 M⊙) a significantly more likely pathway given that heavy seeds have an abundance pattern than is close to and likely in excess of 10−4 compared to light seeds. Finally, we examine the current state-of-the-art in numerical calculations and recent observations and plot a path forward for near-future advances in both domains.
Anti-Universe And Emergent Gravity and the Dark UniverseSérgio Sacani
Recent theoretical progress indicates that spacetime and gravity emerge together from the entanglement structure of an underlying microscopic theory. These ideas are best understood in Anti-de Sitter space, where they rely on the area law for entanglement entropy. The extension to de Sitter space requires taking into account the entropy and temperature associated with the cosmological horizon. Using insights from string theory, black hole physics and quantum information theory we argue that the positive dark energy leads to a thermal volume law contribution to the entropy that overtakes the area law precisely at the cosmological horizon. Due to the competition between area and volume law entanglement the microscopic de Sitter states do not thermalise at sub-Hubble scales: they exhibit memory effects in the form of an entropy displacement caused by matter. The emergent laws of gravity contain an additional ‘dark’ gravitational force describing the ‘elastic’ response due to the entropy displacement. We derive an estimate of the strength of this extra force in terms of the baryonic mass, Newton’s constant and the Hubble acceleration scale a0 = cH0, and provide evidence for the fact that this additional ‘dark gravity force’ explains the observed phenomena in galaxies and clusters currently attributed to dark matter.
The binding of cosmological structures by massless topological defectsSérgio Sacani
Assuming spherical symmetry and weak field, it is shown that if one solves the Poisson equation or the Einstein field
equations sourced by a topological defect, i.e. a singularity of a very specific form, the result is a localized gravitational
field capable of driving flat rotation (i.e. Keplerian circular orbits at a constant speed for all radii) of test masses on a thin
spherical shell without any underlying mass. Moreover, a large-scale structure which exploits this solution by assembling
concentrically a number of such topological defects can establish a flat stellar or galactic rotation curve, and can also deflect
light in the same manner as an equipotential (isothermal) sphere. Thus, the need for dark matter or modified gravity theory is
mitigated, at least in part.
EWOCS-I: The catalog of X-ray sources in Westerlund 1 from the Extended Weste...Sérgio Sacani
Context. With a mass exceeding several 104 M⊙ and a rich and dense population of massive stars, supermassive young star clusters
represent the most massive star-forming environment that is dominated by the feedback from massive stars and gravitational interactions
among stars.
Aims. In this paper we present the Extended Westerlund 1 and 2 Open Clusters Survey (EWOCS) project, which aims to investigate
the influence of the starburst environment on the formation of stars and planets, and on the evolution of both low and high mass stars.
The primary targets of this project are Westerlund 1 and 2, the closest supermassive star clusters to the Sun.
Methods. The project is based primarily on recent observations conducted with the Chandra and JWST observatories. Specifically,
the Chandra survey of Westerlund 1 consists of 36 new ACIS-I observations, nearly co-pointed, for a total exposure time of 1 Msec.
Additionally, we included 8 archival Chandra/ACIS-S observations. This paper presents the resulting catalog of X-ray sources within
and around Westerlund 1. Sources were detected by combining various existing methods, and photon extraction and source validation
were carried out using the ACIS-Extract software.
Results. The EWOCS X-ray catalog comprises 5963 validated sources out of the 9420 initially provided to ACIS-Extract, reaching a
photon flux threshold of approximately 2 × 10−8 photons cm−2
s
−1
. The X-ray sources exhibit a highly concentrated spatial distribution,
with 1075 sources located within the central 1 arcmin. We have successfully detected X-ray emissions from 126 out of the 166 known
massive stars of the cluster, and we have collected over 71 000 photons from the magnetar CXO J164710.20-455217.
The debris of the ‘last major merger’ is dynamically youngSérgio Sacani
The Milky Way’s (MW) inner stellar halo contains an [Fe/H]-rich component with highly eccentric orbits, often referred to as the
‘last major merger.’ Hypotheses for the origin of this component include Gaia-Sausage/Enceladus (GSE), where the progenitor
collided with the MW proto-disc 8–11 Gyr ago, and the Virgo Radial Merger (VRM), where the progenitor collided with the
MW disc within the last 3 Gyr. These two scenarios make different predictions about observable structure in local phase space,
because the morphology of debris depends on how long it has had to phase mix. The recently identified phase-space folds in Gaia
DR3 have positive caustic velocities, making them fundamentally different than the phase-mixed chevrons found in simulations
at late times. Roughly 20 per cent of the stars in the prograde local stellar halo are associated with the observed caustics. Based
on a simple phase-mixing model, the observed number of caustics are consistent with a merger that occurred 1–2 Gyr ago.
We also compare the observed phase-space distribution to FIRE-2 Latte simulations of GSE-like mergers, using a quantitative
measurement of phase mixing (2D causticality). The observed local phase-space distribution best matches the simulated data
1–2 Gyr after collision, and certainly not later than 3 Gyr. This is further evidence that the progenitor of the ‘last major merger’
did not collide with the MW proto-disc at early times, as is thought for the GSE, but instead collided with the MW disc within
the last few Gyr, consistent with the body of work surrounding the VRM.
Observation of Io’s Resurfacing via Plume Deposition Using Ground-based Adapt...Sérgio Sacani
Since volcanic activity was first discovered on Io from Voyager images in 1979, changes
on Io’s surface have been monitored from both spacecraft and ground-based telescopes.
Here, we present the highest spatial resolution images of Io ever obtained from a groundbased telescope. These images, acquired by the SHARK-VIS instrument on the Large
Binocular Telescope, show evidence of a major resurfacing event on Io’s trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images
show that a plume deposit from a powerful eruption at Pillan Patera has covered part
of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Io’s surface using adaptive
optics at visible wavelengths.
Earliest Galaxies in the JADES Origins Field: Luminosity Function and Cosmic ...Sérgio Sacani
We characterize the earliest galaxy population in the JADES Origins Field (JOF), the deepest
imaging field observed with JWST. We make use of the ancillary Hubble optical images (5 filters
spanning 0.4−0.9µm) and novel JWST images with 14 filters spanning 0.8−5µm, including 7 mediumband filters, and reaching total exposure times of up to 46 hours per filter. We combine all our data
at > 2.3µm to construct an ultradeep image, reaching as deep as ≈ 31.4 AB mag in the stack and
30.3-31.0 AB mag (5σ, r = 0.1” circular aperture) in individual filters. We measure photometric
redshifts and use robust selection criteria to identify a sample of eight galaxy candidates at redshifts
z = 11.5 − 15. These objects show compact half-light radii of R1/2 ∼ 50 − 200pc, stellar masses of
M⋆ ∼ 107−108M⊙, and star-formation rates of SFR ∼ 0.1−1 M⊙ yr−1
. Our search finds no candidates
at 15 < z < 20, placing upper limits at these redshifts. We develop a forward modeling approach to
infer the properties of the evolving luminosity function without binning in redshift or luminosity that
marginalizes over the photometric redshift uncertainty of our candidate galaxies and incorporates the
impact of non-detections. We find a z = 12 luminosity function in good agreement with prior results,
and that the luminosity function normalization and UV luminosity density decline by a factor of ∼ 2.5
from z = 12 to z = 14. We discuss the possible implications of our results in the context of theoretical
models for evolution of the dark matter halo mass function.
THE IMPORTANCE OF MARTIAN ATMOSPHERE SAMPLE RETURN.Sérgio Sacani
The return of a sample of near-surface atmosphere from Mars would facilitate answers to several first-order science questions surrounding the formation and evolution of the planet. One of the important aspects of terrestrial planet formation in general is the role that primary atmospheres played in influencing the chemistry and structure of the planets and their antecedents. Studies of the martian atmosphere can be used to investigate the role of a primary atmosphere in its history. Atmosphere samples would also inform our understanding of the near-surface chemistry of the planet, and ultimately the prospects for life. High-precision isotopic analyses of constituent gases are needed to address these questions, requiring that the analyses are made on returned samples rather than in situ.
Multi-source connectivity as the driver of solar wind variability in the heli...Sérgio Sacani
The ambient solar wind that flls the heliosphere originates from multiple
sources in the solar corona and is highly structured. It is often described
as high-speed, relatively homogeneous, plasma streams from coronal
holes and slow-speed, highly variable, streams whose source regions are
under debate. A key goal of ESA/NASA’s Solar Orbiter mission is to identify
solar wind sources and understand what drives the complexity seen in the
heliosphere. By combining magnetic feld modelling and spectroscopic
techniques with high-resolution observations and measurements, we show
that the solar wind variability detected in situ by Solar Orbiter in March
2022 is driven by spatio-temporal changes in the magnetic connectivity to
multiple sources in the solar atmosphere. The magnetic feld footpoints
connected to the spacecraft moved from the boundaries of a coronal hole
to one active region (12961) and then across to another region (12957). This
is refected in the in situ measurements, which show the transition from fast
to highly Alfvénic then to slow solar wind that is disrupted by the arrival of
a coronal mass ejection. Our results describe solar wind variability at 0.5 au
but are applicable to near-Earth observatories.
Gliese 12 b: A Temperate Earth-sized Planet at 12 pc Ideal for Atmospheric Tr...Sérgio Sacani
Recent discoveries of Earth-sized planets transiting nearby M dwarfs have made it possible to characterize the
atmospheres of terrestrial planets via follow-up spectroscopic observations. However, the number of such planets
receiving low insolation is still small, limiting our ability to understand the diversity of the atmospheric
composition and climates of temperate terrestrial planets. We report the discovery of an Earth-sized planet
transiting the nearby (12 pc) inactive M3.0 dwarf Gliese 12 (TOI-6251) with an orbital period (Porb) of 12.76 days.
The planet, Gliese 12 b, was initially identified as a candidate with an ambiguous Porb from TESS data. We
confirmed the transit signal and Porb using ground-based photometry with MuSCAT2 and MuSCAT3, and
validated the planetary nature of the signal using high-resolution images from Gemini/NIRI and Keck/NIRC2 as
well as radial velocity (RV) measurements from the InfraRed Doppler instrument on the Subaru 8.2 m telescope
and from CARMENES on the CAHA 3.5 m telescope. X-ray observations with XMM-Newton showed the host
star is inactive, with an X-ray-to-bolometric luminosity ratio of log 5.7 L L X bol » - . Joint analysis of the light
curves and RV measurements revealed that Gliese 12 b has a radius of 0.96 ± 0.05 R⊕,a3σ mass upper limit of
3.9 M⊕, and an equilibrium temperature of 315 ± 6 K assuming zero albedo. The transmission spectroscopy metric
(TSM) value of Gliese 12 b is close to the TSM values of the TRAPPIST-1 planets, adding Gliese 12 b to the small
list of potentially terrestrial, temperate planets amenable to atmospheric characterization with JWST.
Gliese 12 b, a temperate Earth-sized planet at 12 parsecs discovered with TES...Sérgio Sacani
We report on the discovery of Gliese 12 b, the nearest transiting temperate, Earth-sized planet found to date. Gliese 12 is a
bright (V = 12.6 mag, K = 7.8 mag) metal-poor M4V star only 12.162 ± 0.005 pc away from the Solar system with one of the
lowest stellar activity levels known for M-dwarfs. A planet candidate was detected by TESS based on only 3 transits in sectors
42, 43, and 57, with an ambiguity in the orbital period due to observational gaps. We performed follow-up transit observations
with CHEOPS and ground-based photometry with MINERVA-Australis, SPECULOOS, and Purple Mountain Observatory,
as well as further TESS observations in sector 70. We statistically validate Gliese 12 b as a planet with an orbital period of
12.76144 ± 0.00006 d and a radius of 1.0 ± 0.1 R⊕, resulting in an equilibrium temperature of ∼315 K. Gliese 12 b has excellent
future prospects for precise mass measurement, which may inform how planetary internal structure is affected by the stellar
compositional environment. Gliese 12 b also represents one of the best targets to study whether Earth-like planets orbiting cool
stars can retain their atmospheres, a crucial step to advance our understanding of habitability on Earth and across the galaxy.
The importance of continents, oceans and plate tectonics for the evolution of...Sérgio Sacani
Within the uncertainties of involved astronomical and biological parameters, the Drake Equation
typically predicts that there should be many exoplanets in our galaxy hosting active, communicative
civilizations (ACCs). These optimistic calculations are however not supported by evidence, which is
often referred to as the Fermi Paradox. Here, we elaborate on this long-standing enigma by showing
the importance of planetary tectonic style for biological evolution. We summarize growing evidence
that a prolonged transition from Mesoproterozoic active single lid tectonics (1.6 to 1.0 Ga) to modern
plate tectonics occurred in the Neoproterozoic Era (1.0 to 0.541 Ga), which dramatically accelerated
emergence and evolution of complex species. We further suggest that both continents and oceans
are required for ACCs because early evolution of simple life must happen in water but late evolution
of advanced life capable of creating technology must happen on land. We resolve the Fermi Paradox
(1) by adding two additional terms to the Drake Equation: foc
(the fraction of habitable exoplanets
with significant continents and oceans) and fpt
(the fraction of habitable exoplanets with significant
continents and oceans that have had plate tectonics operating for at least 0.5 Ga); and (2) by
demonstrating that the product of foc
and fpt
is very small (< 0.00003–0.002). We propose that the lack
of evidence for ACCs reflects the scarcity of long-lived plate tectonics and/or continents and oceans on
exoplanets with primitive life.
A Giant Impact Origin for the First Subduction on EarthSérgio Sacani
Hadean zircons provide a potential record of Earth's earliest subduction 4.3 billion years ago. Itremains enigmatic how subduction could be initiated so soon after the presumably Moon‐forming giant impact(MGI). Earlier studies found an increase in Earth's core‐mantle boundary (CMB) temperature due to theaccumulation of the impactor's core, and our recent work shows Earth's lower mantle remains largely solid, withsome of the impactor's mantle potentially surviving as the large low‐shear velocity provinces (LLSVPs). Here,we show that a hot post‐impact CMB drives the initiation of strong mantle plumes that can induce subductioninitiation ∼200 Myr after the MGI. 2D and 3D thermomechanical computations show that a high CMBtemperature is the primary factor triggering early subduction, with enrichment of heat‐producing elements inLLSVPs as another potential factor. The models link the earliest subduction to the MGI with implications forunderstanding the diverse tectonic regimes of rocky planets.
Climate extremes likely to drive land mammal extinction during next supercont...Sérgio Sacani
Mammals have dominated Earth for approximately 55 Myr thanks to their
adaptations and resilience to warming and cooling during the Cenozoic. All
life will eventually perish in a runaway greenhouse once absorbed solar
radiation exceeds the emission of thermal radiation in several billions of
years. However, conditions rendering the Earth naturally inhospitable to
mammals may develop sooner because of long-term processes linked to
plate tectonics (short-term perturbations are not considered here). In
~250 Myr, all continents will converge to form Earth’s next supercontinent,
Pangea Ultima. A natural consequence of the creation and decay of Pangea
Ultima will be extremes in pCO2 due to changes in volcanic rifting and
outgassing. Here we show that increased pCO2, solar energy (F⨀;
approximately +2.5% W m−2 greater than today) and continentality (larger
range in temperatures away from the ocean) lead to increasing warming
hostile to mammalian life. We assess their impact on mammalian
physiological limits (dry bulb, wet bulb and Humidex heat stress indicators)
as well as a planetary habitability index. Given mammals’ continued survival,
predicted background pCO2 levels of 410–816 ppm combined with increased
F⨀ will probably lead to a climate tipping point and their mass extinction.
The results also highlight how global landmass configuration, pCO2 and F⨀
play a critical role in planetary habitability.
Constraints on Neutrino Natal Kicks from Black-Hole Binary VFTS 243Sérgio Sacani
The recently reported observation of VFTS 243 is the first example of a massive black-hole binary
system with negligible binary interaction following black-hole formation. The black-hole mass (≈10M⊙)
and near-circular orbit (e ≈ 0.02) of VFTS 243 suggest that the progenitor star experienced complete
collapse, with energy-momentum being lost predominantly through neutrinos. VFTS 243 enables us to
constrain the natal kick and neutrino-emission asymmetry during black-hole formation. At 68% confidence
level, the natal kick velocity (mass decrement) is ≲10 km=s (≲1.0M⊙), with a full probability distribution
that peaks when ≈0.3M⊙ were ejected, presumably in neutrinos, and the black hole experienced a natal
kick of 4 km=s. The neutrino-emission asymmetry is ≲4%, with best fit values of ∼0–0.2%. Such a small
neutrino natal kick accompanying black-hole formation is in agreement with theoretical predictions.
Detectability of Solar Panels as a TechnosignatureSérgio Sacani
In this work, we assess the potential detectability of solar panels made of silicon on an Earth-like
exoplanet as a potential technosignature. Silicon-based photovoltaic cells have high reflectance in the
UV-VIS and in the near-IR, within the wavelength range of a space-based flagship mission concept
like the Habitable Worlds Observatory (HWO). Assuming that only solar energy is used to provide
the 2022 human energy needs with a land cover of ∼ 2.4%, and projecting the future energy demand
assuming various growth-rate scenarios, we assess the detectability with an 8 m HWO-like telescope.
Assuming the most favorable viewing orientation, and focusing on the strong absorption edge in the
ultraviolet-to-visible (0.34 − 0.52 µm), we find that several 100s of hours of observation time is needed
to reach a SNR of 5 for an Earth-like planet around a Sun-like star at 10pc, even with a solar panel
coverage of ∼ 23% land coverage of a future Earth. We discuss the necessity of concepts like Kardeshev
Type I/II civilizations and Dyson spheres, which would aim to harness vast amounts of energy. Even
with much larger populations than today, the total energy use of human civilization would be orders of
magnitude below the threshold for causing direct thermal heating or reaching the scale of a Kardashev
Type I civilization. Any extraterrrestrial civilization that likewise achieves sustainable population
levels may also find a limit on its need to expand, which suggests that a galaxy-spanning civilization
as imagined in the Fermi paradox may not exist.
Jet reorientation in central galaxies of clusters and groups: insights from V...Sérgio Sacani
Recent observations of galaxy clusters and groups with misalignments between their central AGN jets
and X-ray cavities, or with multiple misaligned cavities, have raised concerns about the jet – bubble
connection in cooling cores, and the processes responsible for jet realignment. To investigate the
frequency and causes of such misalignments, we construct a sample of 16 cool core galaxy clusters and
groups. Using VLBA radio data we measure the parsec-scale position angle of the jets, and compare
it with the position angle of the X-ray cavities detected in Chandra data. Using the overall sample
and selected subsets, we consistently find that there is a 30% – 38% chance to find a misalignment
larger than ∆Ψ = 45◦ when observing a cluster/group with a detected jet and at least one cavity. We
determine that projection may account for an apparently large ∆Ψ only in a fraction of objects (∼35%),
and given that gas dynamical disturbances (as sloshing) are found in both aligned and misaligned
systems, we exclude environmental perturbation as the main driver of cavity – jet misalignment.
Moreover, we find that large misalignments (up to ∼ 90◦
) are favored over smaller ones (45◦ ≤ ∆Ψ ≤
70◦
), and that the change in jet direction can occur on timescales between one and a few tens of Myr.
We conclude that misalignments are more likely related to actual reorientation of the jet axis, and we
discuss several engine-based mechanisms that may cause these dramatic changes.
PPT on Direct Seeded Rice presented at the three-day 'Training and Validation Workshop on Modules of Climate Smart Agriculture (CSA) Technologies in South Asia' workshop on April 22, 2024.
When I was asked to give a companion lecture in support of ‘The Philosophy of Science’ (https://shorturl.at/4pUXz) I decided not to walk through the detail of the many methodologies in order of use. Instead, I chose to employ a long standing, and ongoing, scientific development as an exemplar. And so, I chose the ever evolving story of Thermodynamics as a scientific investigation at its best.
Conducted over a period of >200 years, Thermodynamics R&D, and application, benefitted from the highest levels of professionalism, collaboration, and technical thoroughness. New layers of application, methodology, and practice were made possible by the progressive advance of technology. In turn, this has seen measurement and modelling accuracy continually improved at a micro and macro level.
Perhaps most importantly, Thermodynamics rapidly became a primary tool in the advance of applied science/engineering/technology, spanning micro-tech, to aerospace and cosmology. I can think of no better a story to illustrate the breadth of scientific methodologies and applications at their best.
ESR spectroscopy in liquid food and beverages.pptxPRIYANKA PATEL
With increasing population, people need to rely on packaged food stuffs. Packaging of food materials requires the preservation of food. There are various methods for the treatment of food to preserve them and irradiation treatment of food is one of them. It is the most common and the most harmless method for the food preservation as it does not alter the necessary micronutrients of food materials. Although irradiated food doesn’t cause any harm to the human health but still the quality assessment of food is required to provide consumers with necessary information about the food. ESR spectroscopy is the most sophisticated way to investigate the quality of the food and the free radicals induced during the processing of the food. ESR spin trapping technique is useful for the detection of highly unstable radicals in the food. The antioxidant capability of liquid food and beverages in mainly performed by spin trapping technique.
Sexuality - Issues, Attitude and Behaviour - Applied Social Psychology - Psyc...PsychoTech Services
A proprietary approach developed by bringing together the best of learning theories from Psychology, design principles from the world of visualization, and pedagogical methods from over a decade of training experience, that enables you to: Learn better, faster!
The cost of acquiring information by natural selectionCarl Bergstrom
This is a short talk that I gave at the Banff International Research Station workshop on Modeling and Theory in Population Biology. The idea is to try to understand how the burden of natural selection relates to the amount of information that selection puts into the genome.
It's based on the first part of this research paper:
The cost of information acquisition by natural selection
Ryan Seamus McGee, Olivia Kosterlitz, Artem Kaznatcheev, Benjamin Kerr, Carl T. Bergstrom
bioRxiv 2022.07.02.498577; doi: https://doi.org/10.1101/2022.07.02.498577
(June 12, 2024) Webinar: Development of PET theranostics targeting the molecu...Scintica Instrumentation
Targeting Hsp90 and its pathogen Orthologs with Tethered Inhibitors as a Diagnostic and Therapeutic Strategy for cancer and infectious diseases with Dr. Timothy Haystead.
Immersive Learning That Works: Research Grounding and Paths ForwardLeonel Morgado
We will metaverse into the essence of immersive learning, into its three dimensions and conceptual models. This approach encompasses elements from teaching methodologies to social involvement, through organizational concerns and technologies. Challenging the perception of learning as knowledge transfer, we introduce a 'Uses, Practices & Strategies' model operationalized by the 'Immersive Learning Brain' and ‘Immersion Cube’ frameworks. This approach offers a comprehensive guide through the intricacies of immersive educational experiences and spotlighting research frontiers, along the immersion dimensions of system, narrative, and agency. Our discourse extends to stakeholders beyond the academic sphere, addressing the interests of technologists, instructional designers, and policymakers. We span various contexts, from formal education to organizational transformation to the new horizon of an AI-pervasive society. This keynote aims to unite the iLRN community in a collaborative journey towards a future where immersive learning research and practice coalesce, paving the way for innovative educational research and practice landscapes.
Authoring a personal GPT for your research and practice: How we created the Q...Leonel Morgado
Thematic analysis in qualitative research is a time-consuming and systematic task, typically done using teams. Team members must ground their activities on common understandings of the major concepts underlying the thematic analysis, and define criteria for its development. However, conceptual misunderstandings, equivocations, and lack of adherence to criteria are challenges to the quality and speed of this process. Given the distributed and uncertain nature of this process, we wondered if the tasks in thematic analysis could be supported by readily available artificial intelligence chatbots. Our early efforts point to potential benefits: not just saving time in the coding process but better adherence to criteria and grounding, by increasing triangulation between humans and artificial intelligence. This tutorial will provide a description and demonstration of the process we followed, as two academic researchers, to develop a custom ChatGPT to assist with qualitative coding in the thematic data analysis process of immersive learning accounts in a survey of the academic literature: QUAL-E Immersive Learning Thematic Analysis Helper. In the hands-on time, participants will try out QUAL-E and develop their ideas for their own qualitative coding ChatGPT. Participants that have the paid ChatGPT Plus subscription can create a draft of their assistants. The organizers will provide course materials and slide deck that participants will be able to utilize to continue development of their custom GPT. The paid subscription to ChatGPT Plus is not required to participate in this workshop, just for trying out personal GPTs during it.
Farming systems analysis: what have we learnt?.pptx
DYNAMICAL ANALYSIS OF THE DARK MATTER AND CENTRAL BLACK HOLE MASS IN THE DWARF SPHEROIDAL LEO I
1. Draft version November 10, 2021
Typeset using L
A
TEX twocolumn style in AASTeX61
DYNAMICAL ANALYSIS OF THE DARK MATTER AND CENTRAL BLACK HOLE MASS IN THE DWARF
SPHEROIDAL LEO I
M. J. Bustamante-Rosell1
, Eva Noyola2
, Karl Gebhardt2
, Maximilian H. Fabricius3
,
Ximena Mazzalay3
, Jens Thomas3
, Greg Zeimann2
1
Department of Physics, The University of Texas at Austin, 2515 Speedway, Austin, Texas, 78712-1206, USA
2
Department of Astronomy, The University of Texas at Austin, 2515 Speedway, Austin, Texas, 78712-1206,
USA
3
Max Planck Institute for Extraterrestrial Physics, Giessenbachstraße, 85748 Garching, Germany
(Dated: November 10, 2021)
ABSTRACT
We measure the central kinematics for the dwarf spheroidal galaxy Leo I using integrated-light measurements and
previously published data. We find a steady rise in the velocity dispersion from 30000
into the center. The integrated-
light kinematics provide a velocity dispersion of 11.76±0.66 km s−1
inside 7500
. After applying appropriate corrections
to crowding in the central regions, we achieve consistent velocity dispersion values using velocities from individual stars.
Crowding corrections need to be applied when targeting individual stars in high density stellar environments. From
integrated light, we measure the surface brightness profile and find a shallow cusp towards the center. Axisymmetric,
orbit-based models measure the stellar mass-to-light ratio, black hole mass and parameters for a dark matter halo. At
large radii it is important to consider possible tidal effects from the Milky Way so we include a variety of assumptions
regarding the tidal radius. For every set of assumptions, models require a central black hole consistent with a mass
3.3 ± 2×106
M . The no-black-hole case for any of our assumptions is excluded at over 95% significance, with
6.4 < ∆χ2
< 14. A black hole of this mass would have significant effect on dwarf galaxy formation and evolution.
The dark halo parameters are heavily affected by the assumptions for the tidal radii, with the circular velocity only
constrained to be above 30 km s−1
. Reasonable assumptions for the tidal radius result in stellar orbits consistent with
an isotropic distribution in the velocities. These more realistic models only show strong constraints for the mass of
the central black hole.
Corresponding author: M. J. B. Rosell
majoburo@utexas.edu
arXiv:2111.04770v1
[astro-ph.GA]
8
Nov
2021
2. 2
1. INTRODUCTION
The study of dwarf spheroidal galaxies (dSphs) within
the Local Group provides a unique opportunity to char-
acterize in detail the structure of dark matter (DM) sub-
haloes (e.g., Mateo et al. 1993; Walker et al. 2009; Lokas
2009; Boylan-Kolchin et al. 2013; Hui et al. 2017). When
compared to other galaxies, dSphs are relatively simple
to both measure and simulate, which allows us to make
reliable inferences on their parameters, and therefore,
better constrain DM properties. They are close enough
to provide individual dynamical tracers (i.e. individu-
ally resolved stars), and they currently have relatively
insignificant contribution from baryons (again, when
compared to other galaxies), allowing for a more robust
estimation of their dynamical properties and their DM
profiles. It is because of this simplicity that some of
the most stringent tests of DM properties determined
from galaxies come from studies of dSphs. For exam-
ple, Strigari et al. (2008) showed that within a radius of
300 pc all Milky Way dSphs have dynamical masses of
M300 ∼ 107
M , despite the fact that they span four or-
ders of magnitude in luminosity. This implies that there
is a characteristic inner mass scale for DM halos, below
which, depending on the nature of DM, they either can-
not form stars or just simply do not exist.
The nature of DM has also been put to question when
pure ΛCDM simulations failed to agree with observa-
tions of DM halo abundances and the DM halo profiles
of dSphs. These differences can be categorized into the
“missing satellites problem” (Klypin et al. 1999), i.e. the
overabundance of DM subhaloes in pure ΛCDM simula-
tions with respect to observations, and the “core/cusp
problem”(e.g. Moore 1994; Flores & Primack 1994;
Battaglia et al. 2008; Walker & Penarrubia 2011; Amor-
isco & Evans 2012; Agnello & Evans 2012; Adams et al.
2014; Oh et al. 2015), or the cored nature of central DM
density profiles in observations in discrepancy with the
cuspier nature of the same in pure ΛCDM simulations.
These two discrepancies left room for a variety of ex-
otic forms of dark matter to better fit observations (e.g.
Colin et al. 2000, 2008; Lovell et al. 2012).
Most recent work shows that including baryonic
physics in the simulations flattens the otherwise cuspy
cores, without the need to invoke self-interacting DM
(Pontzen & Governato 2012; Battaglia et al. 2013; Di
Cintio et al. 2014; Del Popolo & Le Delliou 2017).
Furthermore, observational results for systems mostly
dominated by DM are not decisive as to the shape of the
central profile. Most studies show cored central densi-
ties (e.g., Walker et al. 2009; Breddels et al. 2013; Leung
et al. 2020; Read et al. 2016), whereas more recent work
show some cusps (Jardel & Gebhardt 2013; Adams et al.
2014; Hayashi et al. 2020). It has also been suggested
that dwarf spheroidals galaxies might contain little or
no DM (Hammer et al. 2019).
An interesting possibility is that dwarf spheroidal
galaxies contain a central black hole. Volonteri & Perna
(2005); Silk (2017); Kormendy & Ho (2013); Amaro-
Seoane et al. (2014) and others have suggested that black
hole formation may be a natural consequence in these
systems in the early universe. There is an empirical cor-
relation between the mass of a black hole and its bulge’s
velocity dispersion known as the black hole-sigma rela-
tion (Gebhardt et al. 2000; Ferrarese & Merritt 2000;
Saglia et al. 2016). These empirical correlations have
not been probed in dSphs, but if they are extrapolated
to this mass regime one might expect to have black holes
with masses of (1 − 10) × 104
M . Amaro-Seoane et al.
2014 further argue that some dwarf systems may in fact
have a larger-than-expected black hole. In this work we
analyze such a system, Leo I, using the same rigorous
dynamical models applied to larger galaxies.
Being among the brightest and furthest of the Milky
Way dSphs has made Leo I the subject of many in-
depth dynamical studies. At 257 ± 13 kpc (Sohn et al.
2013) and with a half-light-radius of 3.
0
40 ± 0.
0
30 (Mc-
Connachie 2012), it provides an important tracer to ex-
plore the Milky Way mass model. Metallicity studies
(Bosler et al. 2006), proper motion (Gaia Collaboration
et al. 2018; Sohn et al. 2013) and radial velocity measure-
ments (Koch et al. 2007; Sohn et al. 2007) have accrued
a significant amount of data on the galaxy. These data
have been extensively analyzed by various groups, both
by statistical comparison with simulations and by direct
comparison with several Jeans spherical dynamical mod-
els, yet often times contradictory pictures emerge, with
Mateo et al. (2008) finding evidence for an extended DM
halo from observing a flat rotation curve at large radii,
and Lokas et al. (2008) finding a DM profile similar to
the stellar profile. All recent analyses find a V -band
M/L value in the range 8 − 15, which is on the low end
for Milky Way dSph satellites.
In this paper, we measure the stellar light profile and
explore the central dynamics using new integrated-light
kinematic measurements and orbit-based modeling that
allows for a generic stellar velocity anisotropy.
We include kinematics from Mateo et al. (2008) (here-
after referred to as M08), the largest data set available
in the literature, to sample the outer part of the galaxy.
We further consider different aspects of the tidal effects
from the Milky Way. Section 2 presents the new kine-
matic observations using VIRUS-W on McDonald Ob-
servatory 2.7m. Section 3 provides a measure of the
projected number density profile, and corresponding 3d
3. 3
density profile. Section 4 presents the integrated-light
measurements and all kinematic tracers used in the dy-
namical models. An important aspect of the kinematic
extractions is to understand the effect that crowding
from neighboring stars has on the measured spectra; this
effect is described in Section 5. Section 6 examines the
implications of tidal effects using various models. Sec-
tion 7 presents the dynamical models. In Section 8 we
discuss the implications of our work.
2. OBSERVATIONS AND DATA REDUCTION
VIRUS-W (Fabricius et al. 2012) is an integral field
unit (IFU) spectrograph on the McDonald Observatory
2.7 m Harlan J. Smith Telescope and an ideal instrument
for low velocity dispersion systems like dSphs due to the
high spectral resolving power. At R ∼ 8600 and wave-
length coverage of 4855– 5475 Å, VIRUS-W is suited to
measure stellar velocities accurate to around 1 km s−1
and integrated velocity dispersions to about 10 km s−1
.
VIRUS-W is composed of 267 3.
00
2 diameter fibers with
a total field-of-view of 10500
× 5500
(wide side aligned
east-west) and a 1/3 fill factor.
The locations of the fibers are known to about 0.
00
2,
after calibration of the field center. We use stars within
the IFU and stars within the guider field to calibrate the
IFU center. With 3.
00
2 diameter fibers, imaging FWHM
ranging from 100
to 200
, and the fact that we will sum
spectra over a large radial and angular extent, the point-
ing error is negligible.
The VIRUS-W observations in this paper were carried
out over 2 nights in January 2017 (Pointing 1) and 4
nights in February 2017 (Pointing 2) (see Figure 1). The
conditions were mostly clear and were monitored using
the guider stars’ FWHM and photometric magnitude.
Each night we obtained twilight flats, Hg and Ne arc
lamps, dome flats, and bias exposures for calibration.
We employed an observing strategy which included two
3600 s target exposures with two adjacent 1800 s sky
nod exposures, amounting to a total observed time of
30 hr.
For the reductions, we use Panacea1
, a general IFU
reduction package from McDonald Observatory. Many
of the routines employed in this package are similar to
standard IFU reduction codes but we describe them in
detail here. Starting from the raw images, we subtract
and trim the overscan average value and region. We
construct a single master bias frame over many nights
and subtract the resultant image from our science and
twilight frames. Using the twilight frames, we build a
wavelength solution and a trace model for each of our
1 https://github.com/grzeimann/Panacea
Figure 1. The VIRUS-W and M08 footprints overlaid on
an SDSS Leo I image. The VIRUS-W footprint is 10500
×
5500
. We show January-February 2017 pointings 1 (blue) and
2 (red), as well as M08 targets in green. The lower panel
shows a zoomed image, with the photometric center of the
galaxy marked with a yellow plus sign.
fibers. Twilights are taken at least once a night typi-
cally in the evening and morning. As the ambient tem-
perature changes, there are slight shifts in the trace of
the fibers which are measurable in each of our science
frames. We use these derived shifts to correct our trace
model for individual science frames. For the shorter ex-
posure (lower-signal) 1800 s sky frames we interpolate
between the two closest science or twilight frames to get
an adjusted trace model.
In order to properly extract the amount of flux de-
posited in each pixel of the CCD by a given fiber, we
use the normalized fiber profile weights given by our twi-
lights. For each individual fiber, CCD column by CCD
column, we solve a system of linear equations defined
as A x = b, where A is a matrix whose entries are the
normalized fiber profile weights for the given column for
each fiber, b is the column of CCD data from a given
science or sky frame, and x is the vector for which we
solve that gives the spectrum for each fiber for the given
column. The spectral extraction is not done in rectified
coordinates (coordinates curved to follow the trace of
4. 4
the diffraction pattern on the CCD) because the curva-
ture of the trace is small enough that the error in not
rectifying coordinates is less than 1% for the whole CCD.
The need for long science observations due to the low
luminosity of the object carries along the problem of
non-linear variations between the two bracketing sky
observations. To further extract these non-linear varia-
tions we use an iterative sky subtraction algorithm for
the science observations that takes advantage of the fact
that all fibers contain starlight from Leo I. We first build
a master sky frame from each individual sky frame, by
applying an illumination model built from the twilight
frames, which corrects for fiber-to-fiber variations. We
then use time-interpolated master sky spectra to first
subtract the sky from each science frame. Co-adding
the individual science spectra for each VIRUS-W point-
ing gives us two master science models. We subtract
the master science frames from the individual science
frames and use this difference to build new master sky
frames. We iterate this procedure twice for convergence.
The final master sky frames are subtracted from the in-
dividual science exposures and we co-add each pointing
to get our final 534 fiber measurements.
As explained in detail in the kinematics section (Sec-
tion 4), we bin the individual spectra into a polar grid in
order to measure the integrated-light kinematics. Fig-
ure 2 shows our binned spectra.
3. LUMINOSITY DENSITY PROFILE
Dynamical models require a spatial profile of the mass
density in the object of study as an input. The first
step is to estimate the projected surface brightness for
the object. Previous modeling for Leo I used profiles
obtained via star counts from photographic plates (Ir-
win & Hatzidimitriou 1995). As discussed in Noyola &
Gebhardt 2006, within dense regions, star counts suf-
fer from incompleteness due to crowding effects. This
underscores the need to obtain updated density profiles
coming from more recent data sets.
Due to the necessity for wide spatial coverage, we use
publicly available Sloan Digital Sky Survey (SDSS) g-
band imaging (DR12; Alam et al. 2015) for Leo I. We
have to restrict ourselves to a field of 200
in size ow-
ing to the presence of a bright foreground star to the
south of the galaxy. A careful determination of the
galaxy’s center is crucial, especially if one suspects the
existence of a cusp, since miscentering can turn a cuspy
profile into a flat one (but not the other way around).
A photometric catalog was obtained from the SDSS im-
age using daophot (Stetson 1987). We then used the
method described in detail in Noyola & Gebhardt 2006
to determine the center using this catalog. Briefly, the
Figure 2. Spectra in different regions for the VIRUS-W
data. The black line represents the extracted spectra cen-
tered on the Mg regions; the data extend both to the blue
and the red, and we highlight this region. The red line is
the best-fit of the template star convolved with the veloc-
ity profile. There are 23 spatial bins used for the VIRUS-W
spectra, and here we show six representative spectra. The
spatial locations are noted at the bottom of the plots.
method assumes axisymmetry and counts stars in an-
gular slices around a tentative center, searching around
for the minimum variation between slices given slightly
offset centers to the initial guess. Our new derived cen-
ter is 10h08m26.7s +12d18m27.8s, differing only by 2.
00
3
from that of M08.
Using the new central location, we measure the el-
lipticity and position angle of the galaxy. We do
this by smoothing the SDSS image using a bi-weight
convolution boxcar (Beers et al. 1990). We find the
best fit global value for ellipticity and position angle
on the smooth image with values of 0.2 and 80◦
(de-
fined as north through east to the major axis), respec-
tively, which is consistent with the results from Irwin &
Hatzidimitriou 1995. As M08 already noted, the im-
age shows variations in ellipticity and position angle
(PA) with radius, particularly for the central regions.
Since these regions are the most affected by crowding
and therefore shot noise, we opt for using a global fit
5. 5
Table 1. Leo I density profile
log r SB err smooth log r SB err smooth
0.297 21.58 0.35 21.56 2.106 22.45 0.03 22.48
0.632 21.560 0.22 21.63 2.178 22.63 0.04 22.66
0.844 21.66 0.15 21.70 2.250 22.82 0.04 22.89
1.005 21.82 0.13 21.76 2.321 23.12 0.05 23.11
1.140 21.88 0.12 21.80 2.391 23.38 0.07 23.40
1.257 21.80 0.09 21.82 2.461 23.64 0.09 23.66
1.363 21.82 0.07 21.83 2.530 23.94 0.13 23.96
1.460 21.84 0.06 21.85 2.599 24.28 0.22 24.28
1.552 21.86 0.05 21.88 2.668 24.65 0.38 24.57
1.639 21.96 0.05 21.92 2.736 24.97 0.60 24.94
1.722 22.00 0.05 21.98 2.804 25.33 0.95 25.26
1.803 22.04 0.04 22.03 2.948 N/A N/A 25.96
1.881 22.13 0.04 22.08 3.034 N/A N/A 26.39
1.957 22.19 0.04 22.22 3.092 N/A N/A 26.68
2.032 22.31 0.03 22.33 3.150 N/A N/A 26.98
Note—Column (1): log radius in arcseconds; Column (2): mea-
sured photometric points from SDSS image in V magnitudes;
Column (3): photometric error; Column (4): smooth profile in
V magnitudes, including a de Vacouleurs extrapolation at large
radii
with constant ellipticity and PA, which is adequate for
our axisymmetric models.
The last step to obtain a density profile uses a bi-
weight estimator to measure the integrated-light density
in concentric elliptical annuli. This method is used in
Noyola & Gebhardt 2006 for Galactic globular clusters.
We use the profile from M08 to find the photometric
normalization by matching our profiles to theirs at large
radius, where there is excellent agreement between our
photometric points and previous measurements. It is
worth mentioning that even though M08 call their pro-
file “surface brightness” and report it in the correspond-
ing units, the actual measurement is done by repeating
the procedure in Irwin & Hatzidimitriou 1995 on their
new data set. By using isopleths of star counts, their
profile will suffer from the same crowding effects de-
scribed in Noyola & Gebhardt 2006. As can be seen
in Figure 3, every profile agrees quite well within the
30
− 100
radial range, while a large difference is seen
1 10 100 1000
r (arcsec)
20
21
22
23
24
25
26
µ
(V
mag)
SB SDSS
SB ACS
smooth
SC I&H
SB M08
1 10 100 1000
r (parsecs)
Figure 3. Radial surface brightness profiles, both from
star counts and from integrated light. Green: photometric
points from SDSS. Cyan: photometric points from Hubble
Advanced Camera for Surveys (ACS) image. Red: smooth
line based solely on SDSS photometric points. Blue dashed:
star count profile from Irwin & Hatzidimitriou 1995. Ma-
genta: density profile from M08. Every profile is directly
normalized to the M08 line but for the ACS one, normalized
indirectly via SDSS due to radial coverage. The smooth red
line is the one used as input for dynamical models, which
shows a shallow cusp towards the center.
inside 30
. Our surface brightness profile departs from
previous estimates by showing a shallow cusp, while the
star count profiles show a flat central profile. As a test,
we performed the same measurement on the higher res-
olution Hubble Space Telescope (HST) images (Bosler
et al. 2006) used for crowding estimations (see Section
5). Despite their higher resolution, the spatial coverage
of these images is incomplete (only covering out to 10
),
which is why we only use the profile from the SDSS im-
age for our analysis. The higher resolution of the ACS
image resolves many more individual stars, which causes
a larger scatter in the photometric points as can be seen
in the central region in Figure 3. The ACS- and SDSS-
based profiles match well to 400
radius, both tracing a
shallow cusp. Inside 400
there is a small difference but
the amount of light in that difference, and hence stellar
mass, is insignificant, especially given that our first kine-
matic bin includes spectra out to 3000
. The fact that the
analysis of the two independent images yields the same
shape for the central profiles provides confidence that
the detected cusp is real. The detection of this cusp
also gives us confidence in our new center.
As a final step, we smooth the density profile using
a spline Wahba & Wang 1990. We also extrapolate the
profile with an r1/4
law in order to accommodate stars
6. 6
in the dynamical modeling that go beyond the measured
region. This profile is the one used as input in the dy-
namical models. The data are shown in Table 1.
4. KINEMATICS
We use integrated-light kinematics derived from the
VIRUS-W data, and we also include velocities from in-
dividual stars from M08. Each kinematic data set re-
quires different analysis techniques due to the different
spatial densities involved.
Traditional methods for the kinematic study of local
dSphs rely on them being sufficiently close and sparse
to be able to measure the velocity of one star at a time.
The VIRUS-W data, unlike M08’s, is concentrated in
the central densest regions of Leo I, which, compounded
with the fact that VIRUS-W fibers have twice the di-
ameter of M08’s, makes the analysis of individual stellar
spectra virtually impossible.
As discussed in Section 5, most VIRUS-W fibers con-
tain multiple stars. Typically, the brightest star con-
tributes at most 24% of the total light. At this level ex-
tracting individual stellar velocities with VIRUS-W in
the central region of Leo I would be biased. Instead, we
use integrated-light when dealing with VIRUS-W data
(a common method in the study of denser or further
away galaxies, but also Galactic globular clusters). To
make sure we reach a sufficient number of stars for our
analysis, we bin fibers for our kinematic measurements.
The spatial binning of the fibers is defined by the dy-
namical modeling grid, and our minimum number is five
fibers.
The spatial and angular binning on sky for the
VIRUS-W data is given in Fig 4. The number of spec-
tra in each spatial VIRUS-W bin ranges from 5 to 41.
For each spectra we first fit the continuum and divide,
which normalizes each of the spectra so that their con-
tinuum is unity. The fitting to the continuum is done in
fixed wavelength bins, using regions to avoid absorption
lines. We then linearly interpolate across the bin centers
to make a smooth continuum. The co-addition uses a
biweight of the continuum-divided spectra.
We rely on the maximum penalized likelihood method
described in Gebhardt et al. (2000) for our kinematical
measurements. The principle behind this method is to
simultaneously fit the line-of-sight velocity distribution
(LOSVD) and the relative weights on the stellar tem-
plates. We find the best fit to the integrated-light spec-
tra by fitting to the velocity bins of the LOSVD non-
parametrically and adjusting the weights on template
stars observed with VIRUS-W. We further constrain the
LOSVD with a smoothing parameter. As a sanity check,
75 50 25 0 25 50 75
y (arcseconds)
80
60
40
20
0
20
40
x
(arcseconds)
28
13
9
24
25
21 19
27
27
13
36
24 29
36
28
5
27
30 22
41
5
18
24
Figure 4. On-sky spatial and angular binning of the
VIRUS-W data. Axes are aligned with the galaxy’s major
and minor axes as projected in the sky, are in arcseconds,
and represent the distance from the galaxy’s center. The
number overlaying each bin indicates the number of fibers
within it. Archival data, covering the outermost radial bins,
have been omitted for clarity.
we compare our results to those obtained using pPXF
(Cappellari 2016) and find close agreement.
We use five template stars for the kinematic extrac-
tions. These five templates were observed with VIRUS-
W, and have been down selected from a parent sample
of 32 stars. We experimented with a variety of tem-
plates, and the five chosen are representative. We find
insignificant differences in the final kinematics when us-
ing different templates. The templates are processed the
same way for continuum removal as the science spectra.
Finally, we use a subset of the M08 data. M08 per-
formed individual spectral analysis on each of their
fibers via normalized cross-correlations in order to de-
rive individual stellar velocities. Although most of their
fibers were not concentrated in the central regions, they
do target some stars all the way to the center of Leo I.
Further analysis performed in this paper (Section 5) us-
ing HST imaging and simulations shows that this very
likely biased their central individual stellar velocities to-
wards the average velocity of the galaxy. Due to this
bias, we decided against using M08 data where we could
use our own kinematics. We binned the individual data
points from M08 in concentric radial bins for the outer
regions to achieve sufficient numbers for the LOSVDs.
Koch et al. (2007) present a kinematic analysis of Leo I
and show a velocity dispersion profile similar to what
we are using at large radii. Their innermost data point
at 1.
0
3 has a dispersion around 10 km s−1
, consistent
with measurements presented here of 11 km s−1
. They
use additional data inside of that radius from the study
of Mateo et al. (1998) that shows a significantly lower
7. 7
dispersion. The data from the older work is incorporated
within M08. As shown in the following discussion, we
demonstrate why using individual velocities to measure
a dispersion can be biased in crowded regions.
The final LOSVDs result from VIRUS-W measure-
ments in the center bins and radially binned M08 mea-
surements for the outer regions. These LOSVDs and
the uncertainties are input into the dynamical mod-
els. Table 2 shows the velocity dispersions fitted to the
LOSVDs, where we report the values integrated over the
annuli. We note that the dynamical models fit directly
to the LOSVDs, and we only provide the velocity dis-
persions in radial bins for comparison with the models.
Table 2. Leo I Velocity Dispersion Bins
Radius (arcsec) Velocity Dispersion (km s−1
)
15.35 12.0 ± 0.2
38.65 11.5 ± 0.5
53.25 11.8 ± 1.0
75.10 11.0 ± 0.6
200 9.1 ± 0.8
250 9.3 ± 0.9
315 8.6 ± 1.0
390 11.4 ± 1.7
540 10.0 ± 0.8
Note—Leo I bins as a function of radius. The
horizontal line marks the division between the two
datasets, M08 (below) and our VIRUS-W data
(above).
5. THE PROBLEM OF CROWDING
When measuring velocities for individual stars, the
flux contribution of nearby faint stars to a given mea-
sured spectrum, whether they are resolved or unre-
solved, will have the effect of biasing the measured ve-
locity of such spectrum towards the mean velocity of
the galaxy, even if the spectrum has a large contribu-
tion from a single star. This effect has to be taken into
account when measuring velocity dispersion σv from in-
dividual stars in crowded stellar fields, since they will
be biased low if the contribution of unresolved light is
meaningful.
The story is different for kinematic measurements that
use templates stars to extract velocity dispersion from
line broadening of added spectra. In this case the un-
resolved light, or the small contribution from resolved
faint stars, makes a valuable contribution to the line
profile. The analysis has to be very careful dealing with
added spectra where the contribution is dominated by a
single or a few stars. It is in that case that the σv can
be artificially biased low or high.
These effects have been previously discussed in
crowded stellar fields when using IFUs. Lützgendorf
et al. (2015) perform simulations which show that the
contribution of faint stars can bias the velocity disper-
sion measurements to lower values in crowded fields by
large amounts within normal observing conditions. This
bias occurs by influencing the measured individual star
velocities towards the cluster mean due to the diffuse
background light. For sparse fields, the bias can go
either way if a bright star is nearby. Bianchini et al.
(2015) perform detailed simulations on globular clusters
to study this bias as well. The bias they find on the ve-
locity dispersion is stochastic, with a trend towards low
values in the most central regions. For Leo I, we are in
a regime of high crowding and run simulations tuned to
the specific observations and distribution of stars within
the fibers. These effects have been previously discussed
in crowded stellar fields when using IFUs. (Lützgendorf
et al. 2015) perform simulations which show that the
contribution of faint stars can bias the velocity disper-
sion measurements to lower values in crowded fields by
large amounts within normal observing conditions. This
bias occurs by influencing the measured individual star
velocities towards the cluster mean due to the diffuse
background light. For sparse fields, the bias can go
either way if a bright star is nearby. (Bianchini et al.
2015) perform detailed simulations on globular clus-
ters to study this bias as well. They find the bias is
stochastic, with a trend of a bias to low values in the
most central regions. For Leo I, we are in a regime of
high crowding and run simulations tuned to the specific
observations and distribution of stars within the fibers.
The crowding problem is partially mitigated by the
PAMPELMUSE code (Kamann 2018) used in globular
clusters surveyed by MUSE (Alfaro-Cuello et al. 2019;
Kamann 2020). The advantage that PAMPELMUSE
has is that the spatial resolution elements of MUSE are
quite small, so the number of stars within any spaxel is
also small. Therefore, with accurate positions of stars
from HST, one can then better extract individual veloc-
ities by limiting the crowding bias. In our case, with
3.
00
2 fibers and the large point-spread function (PSF),
the number of stars that contribute light to each spaxel
8. 8
is high, making it essentially impossible to provide un-
biased individual velocities.
In this section, we investigate the effects of crowding
on the measurements of radial velocities for individual
fibers on Leo I’s central regions. We use two sets of deep,
high resolution Hubble Space Telescope (HST) imag-
ing to quantify the number of stars and their relative
flux contribution to each fiber. The first set consists of
F435W imaging from the Advanced Camera for Surveys
(ACS) taken on February 2006 with an exposure time of
6800s (GO-10520; PI: Smecker Hane). The second set
contains F555W imaging from the Wide Field Camera 3
(WFC3) taken on January 2011 with an exposure time
of 880s (GO-12304; PI: Holtzman). We create catalogs
from both sets of imaging using daophot (Stetson 1987).
As seen in Figure 5, within our 3.
00
2 diameter fibers we
find a median of 22 stars in our deep HST catalogs. The
brightest star in each fiber has a median contribution of
24% of the total flux. Thus, no single star dominates
the light of our fibers and rather we are capturing the
light from small populations on the order of tens of stars
each. In addition, the point-spread function of the ob-
servations range from 1.
00
5-3.
00
0, blending diffuse star light
even more, and making the extraction of individual ve-
locities yet more biased.
In light of this crowding issue, we choose not to mea-
sure radial velocities from individual VIRUS-W fibers
but rather stack fibers within radial bins and infer the
velocity dispersion from the Mg b triplet absorption fea-
tures. Our kinematic measurements are discussed in
more detail in Section 4.
We also use an archival data set from M08. This pro-
gram was able to target individual, bright RGB stars
which dominated the light in their fiber with some ex-
ceptions. In the central 150 pc of Leo I, HST catalogs
show that the HECTOCHELLE fibers captured the light
from a median of 5 stars not including the central RGB
target with a median contribution of 10.4% from the un-
resolved population. Figure 6 demonstrates the size of
the fibers from VIRUS-W and HECTOCHELLE com-
pared to the HST imaging. Figure 7 uses the informa-
tion for the size and location of the VIRUS-W fibers to
show the effect from crowding.
Motivated to understand the effect crowding might
have on the kinematic measurements of M08 in the cen-
tral regions of Leo I, we devise a simple model. The
idea is to use the star positions and magnitudes from
HST, and simulate the crowding in each spectral ele-
ment (i.e., individual fiber), by measuring the inferred
bias on the velocity of the target star. This correction
will vary across the field depending on the crowding, and
once we have that field-dependent correction, we then
0 20 40 60 80
r (arcsec)
10
20
30
40
50
F
max
Figure 5. Box plot of the maximum percentage of flux from
the brightest star in an individual VIRUS-W fiber vs. radius.
The boxes extend from the first quartile to the third with
the median marked as an orange line. The whiskers extend
from the 5th percentile to the 95th. The flux contribution
is calculated using HST’s deeper catalog. Due to the low
flux contribution of the brightest star, using VIRUS-W to
extract individual stellar velocities in the central region of
Leo I would be biased. Instead, we rely on integrated-light
measurements.
Figure 6. Comparison of a VIRUS-W fiber (black circle of
1.
00
6 radius) and a HECTOCHELLE fiber (white circle of 0.
00
7
radius) placed at the center of the galaxy in the HST deep
image, with cataloged stars overlaid.
9. 9
Figure 7. M08 fibers arranged in terms of maximum flux
from one star within a fiber. The blue points are those cov-
ered by ACS (deep catalog), while the orange points are cov-
ered by WFC3 (shallow catalog). One can see a noticeable
trend of smaller velocity dispersion for lower flux percentage,
and thus the need for taking into account crowding effects.
combine over all spectral elements to generate the bias
on the velocity dispersion. Below we list the six steps
for the process to determine the local correction needed
for each spectral element, for convenience defining the
normal distribution
N(~
x, ~
µ, σ) ≡
1
(2πσ2)dim ~
x/2
e−(~
x−~
µ)2
/(2σ2
)
, (1)
where dim ~
x is the number of components in the vector
~
x.
1. Input star catalog: For each star, we use their po-
sition relative to the center, the point-spread func-
tion (PSF) of the observations, and the magnitude
in order to derive that star’s contribution to the
total flux in the fiber
Fj(Mj, µx, µy) = A 10−0.4×Mj
×
Z r
−r
Z √
r2−x2
−
√
r2−x2
N(~
x, ~
µ, σs)dy dx.
(2)
where σs is FWHM/2.35 of the observations; ~
µ =
(µx, µy) are the coordinates of the star with re-
spect to the fiber center, r is the radius of the fiber,
Mj is the star’s apparent magnitude, ~
x = (x, y)
are Cartesian coordinates centered on the fiber
(r2
= x2
+ y2
), and A is a normalization constant.
2. Spectral profile: Instead of relying on a simple
measure of the velocity shift using a weighted av-
erage of the velocities, we generate an absorption
line in order to be more realistic. The absorp-
tion features in the spectrum of the jth star in the
fiber are modeled with a Gaussian of width σw,
the average sigma of the Mg b absorption lines of
a template star
gj(u) = FjN(u, vj, σw). (3)
3. Velocity sampling: We then generate random sam-
plings of the velocities for each star. The position
of the jth gaussian in spectral space (vj(σ), the
jth star’s velocity) is randomly drawn from a nor-
mal distribution whose standard deviation (i.e., its
velocity dispersion) is selected from range of 0.5–
60 km s−1
. We use a range of input velocity dis-
persions in order to check for effects as a function
of velocity dispersion:
P(vj, σ) = N(vj, 0, σ)
σ ∈ [0.5, 60]
(4)
4. Summed fiber profile: We then generate the final
summed spectrum that will be used for velocity
measurement. For each of the fibers, the gaus-
sians are scaled to their relative flux contribution
Fj computed above and stacked in spectral space.
G(u|σ) =
X
j∈stars
gj(u) (5)
where we explicitly denote the random variable
nature of the dependence on σ to avoid confusion.
5. Velocity centroid: For each fiber, the simulated
spectrum of stacked Gaussians is then cross-
correlated with a normalized Gaussian of width
σw to calculate the radial velocity vm:
max(G(u|σ) ? N(u, 0, σw)) = vm (6)
6. Crowding bias: Finally, we use simulations in or-
der to measure a bias for each particular star
in the specified fiber or slit. For each fiber, we
drew a σ and vj 10,000 times over all stars in the
fiber. Combining these via Equation (6), we ob-
tain 10,000 estimates of the measured velocity in
that fiber, which are then used to compute the
range of velocities measured from that fiber (i.e.,
the standard deviation). Thus, the measured ve-
locity in a fiber vi is drawn from this output dis-
tribution. These simulations provide a map from
input velocity dispersion to output velocity disper-
sion for a given flux distribution of contributing
stars. This map, σi(F̄i, σ), is produced for each
10. 10
40 60 80 100
Fmax
0.0
0.1
0.2
0.3
0.4
0.5
0.6
∆σ/σ
σ = 5 km/s
σ = 10 km/s
σ = 15 km/s
Figure 8. Monte Carlo simulation of the fractional change
in velocity dispersion due to crowding vs. maximum flux per-
centage contribution of one star, per fiber. In the notation of
the equations in this section: (σ − σi(F̄i, σ))/σ vs F̄i. Each
circle represents a fiber. The black vertical line shows the
median maximum flux for VIRUS-W points. Due to crowd-
ing, for any given intrinsic velocity dispersion σ, the velocity
one would measure from that fiber would be one extracted
from a distribution with velocity dispersion σi(F̄i, σ). In
general, more crowding produces a lower maximum flux per
star in fiber and correspondingly, a bigger fractional change
in velocity dispersion.
ith fiber in M08 with HST imaging and is shown
in Figure 8.
At this point, we have determined the local correction
on each fiber, and we combine these local corrections
to determine the effect on the integrated velocity dis-
persion of the co-added fibers within a bin or annuli.
Using our simple model and mapping allows us to con-
struct a maximum likelihood estimator (MLE) for the
velocity dispersion of individual radial velocity measure-
ments from fibers in M08 with crowding issues. The
construction of such an MLE is only applicable to the
fibers with HST coverage, so we restrict our calculations
and adjustments to fibers which satisfy this criterion.
The strength of our estimations relies on the ability of
the catalogs to detect fainter stars. By doing so, we can
estimate the maximum flux percentage of the brightest
star within the fiber and make the appropriate correc-
tions; the shallower the catalog, the smaller the correc-
tions. We measure the difference between the maximum
flux percentage of the brightest star among the different
catalogs. Compared to the shallow catalog from HST,
we obtain 91% ± 8% for M08 and 40% ± 17% for VW.
For the deep catalog from HST, we obtain 79% ± 16%
for M08 and 27% ± 13% for VW. Given the effect be-
tween using the deep or shallow catalog is about a 10%
difference, we use the shallow catalog only when lacking
deeper imaging. This small difference will not impact
the conclusions.
In practice, velocity dispersions are estimated by ra-
dial bins of fibers. For a given radial bin, we calculate
the probability of measuring a particular velocity vmi
,
P(vmi |σi, σe) = N(vmi , µ, σe) ⊗ N(vmi , µ, σi) (7)
Where ⊗ denotes convolution,
µ = µ(σi, σe) =
X
i
vmi
σ2
i + σ2
e
,
X
i
1
σ2
i + σ2
e
, (8)
and
σi = σi(F̄i, σ). (9)
The mapping, σi, is from our simple model above, the
index i represents the ith fiber in the bin, F̄i is the flux
vector of stars in the ith fiber, σe is the radial velocity
measurement error, and σ is the velocity dispersion in
the bin without any crowding correction.
Thus, we maximize the likelihood L(σ) for a given bin
to get our best estimate of the true velocity dispersion.
L(σ) =
N
Y
i
P (vmi |σi, σe) ,
σ = max L(σ)
(10)
Our corrections to the innermost M08 bins are shown
in Figure 9. Even though the coverage is not complete,
one can extrapolate the results to the other fibers mak-
ing use of the surface density profile. These crowding
corrections agree well with the velocities we measured
by binning the spectra of 10-12 fibers and performing
integrated light (c.f. Table 2).
Given the above issues with having to deal with crowd-
ing when using individual velocities, we rely instead on
integrated light measurements in the inner regions for
the dynamical models. As we have shown, the kinemat-
ics from both are in agreement when applying the bias
corrections based on the simulations.
6. TIDAL EFFECTS
11. 11
Figure 9. Estimated corrections for the velocity dispersion
measurements from individual stars in M08 when crowding
is taken into account. The corrections are only for stars
that fall within existing HST images. The orange points
are uncorrected velocities, the blue ones are corrected. The
error bars increase in size, but at every radius the corrected
velocity dispersion increases.
It is important to consider tidal effects from the Milky
Way on Leo I. Since our models assume dynamical equi-
librium, if stars are actively being stripped out of the
gravitational potential, we must include their effect on
the kinematics, or at least quantify the magnitude of
tidally stripped stars. Tidal effects are key to measur-
ing the DM contribution at large radii, but are not ex-
pected to alter the central kinematics. We try a few
tidal models to explore their effects. Early measure-
ments of Leo I’s tidal radius (Irwin & Hatzidimitriou
1995) fit a truncated isothermal sphere to the luminos-
ity under the assumption that mass follows light, esti-
mating a tidal radius of 0.9 ± 0.1 kpc. Sohn et al. 2013
use HST imaging to study the proper motion of Leo I
and infer possible pericentric approaches. With a com-
bination of orbital analysis and Monte Carlo simulations
they predict a fairly elliptical orbit, with a pericentric
passage of 101.0 ± 34.4 kpc. For different Milky Way
models, they find a tidal radius of 3–4 kpc. This result
coincides with Gaia’s DR2 measurement (Gaia Collabo-
ration et al. 2018). Their three different galactic models
give pericentric passages of (89.5+55.9
−47.5 kpc, 112.6+58.4
−60.6
kpc, 86.9+59.2
−44.4 kpc). This result seems at odds with in-
direct orbit estimations made earlier by Sohn et al. 2007
and M08 based mainly on a “break” radius at 400 pc;
beyond this radius, the kinematics show deviations from
axisymmetry in the angular distribution of the velocities
and a rise in the velocity dispersion. N-body simulations
show that such a rise is typically found as an artifact of
the inclusion of tidally unbound stars (Read et al. 2006;
Klimentowski et al. 2007; Muñoz et al. 2008). In accor-
dance with the kinematics, as pointed out by M08, there
is a significant stellar population change at this break
radius, with younger stars being concentrated within it.
Again, it is expected from hybrid hydro/N-body sim-
ulations (as in Mayer et al. 2005) that tidal stirring in
dwarfs would cause strong gaseous inflows leading to en-
hanced central star formation.
Taking this break radius both in stellar composition
and kinematics into consideration as the effect of tides
caused by the Leo I’s closest approach, both papers
(Sohn et al. 2007; Mateo et al. 2008) estimate pericentric
passages smaller than 30 kpc.
In a later paper, Sen et al. 2009, run several signif-
icance tests on M08’s kinematic sample to determine
the robustness of their break radius. They conclude
that even though modest streaming motion of at most
6.2 km s−1
is significant at the 5% confidence level, with
a best fitting break radius of 447 pc, it is still uncon-
strained (from 115.2 pc to 928.9 pc) with that data set.
Lokas et al. 2008 use an “interloper removal” method
to remove unbound stars. Even though shown by the
authors to be satisfactory for a galaxy in which mass
follows light, if the mass-to-light is to increase strongly
with radius (if embedded in a cuspy or cored DM halo,
as shown in Battaglia et al. 2013), it can remove an
important fraction of genuine members and artificially
lead to a declining velocity dispersion.
In light of these discrepancies, we sample different
tidal radii around the best fitting radius considered in
Sen et al. 2009. Our approach uses a dynamical model
for the bound stars and an input number density for
stars that have been tidally removed. For various models
of the tidal radius, we modify the 3D luminosity density
accordingly and calculate the projected dispersion pro-
file for that tidal model. We then compare the disper-
sion profiles of the tidal model to the one with no tidal
effects and hence determine the relative corrections to
the projected kinematics. These relative corrections are
applied to the as-measured dispersion profiles, and the
tidal dispersion kinematic and projected density profiles
are then the inputs for the orbit-based modeling. This
procedure approximates the effects from tidal forces as
input to the dynamical models.
The input dynamical model is an isotropic model fit-
ted to the measured kinematics, assuming all radii are
in dynamical equilibrium. This model then provides 3D
number density and projected kinematic profiles. Thus,
our first assumption considers no tidal effects. Our sec-
ond assumption has a tidal radius of 50500
. For this case
we measure the light in the 3D density that falls outside
12. 12
of 50500
, remove that light from all inner radii, and then
re-measure the projected kinematics and surface bright-
ness profile. The third assumption has a tidal radius of
43000
, for which we perform the same operation. The
ratio of the radial profiles, both surface brightness and
dispersion, between the tidal model and the input dy-
namical model are then applied to the measured quan-
tities.
Figure 10 shows the resulting surface brightness and
velocity dispersion profiles for two selected tidal radii at
43000
and 50500
. As it is evident from the figure and the
calculations, a smaller assumed tidal radius will lower
the velocity dispersions and increase their uncertainties.
The effects are most drastic for the outer bins since a
higher fraction of the light would be tidal light. We
use these modified profiles as part of our modeling, as
explained in Section 7.
As a sanity check on the approach taken above, we can
use a modification to the orbit-based models. We mod-
ify the best-fit orbit model of the full kinematic data set
in a way consistent with the assumptions of tidal effects.
This model includes a dark halo component. Since our
approach assumes that orbits that go beyond the tidal
radius are not considered in dynamical equilibrium and
that their contribution to the projected velocity disper-
sion on the inner bins needs to be removed, we remove
orbits whose energies place them outside of the speci-
fied tidal radius by forcing their weights to zero. In this
way, the resultant orbital distribution should produce
the modified kinematic radial profiles that we assume.
A limitation to this procedure is that replacing or-
bital weights with zero creates an internally inconsistent
model. We remove orbits based on both tidal radii of
43000
and 50500
, and then re-calculate projected kinemat-
ics. In both cases, the velocity dispersion profiles show
similar, but not exact, behavior as in fig. 10. The slope
of the velocity dispersion profiles are nearly the same,
and there is a small (1 km s−1
) offset in normalization.
This normalization is expected since we are removing
mass from the system but not re-calculating the mass
within the orbit model. Since the shape of the velocity
dispersion profile is nearly the same as our approximated
value, we expect the same result for the underlying po-
tential in the central regions.
We stress that our approach to including tidal effects
serves as an aid to understand how tidally-perturbed
stars could modify our conclusions. A proper model
would include the Milky Way’s actual effect on the stel-
lar orbital distribution and surface brightness profile of
the stripped stars. Given the check we performed and
the already large uncertainties on the dark halo, any re-
finement in the models of tidal effects will be minimal.
Figure 10. Velocity dispersion (upper) and luminosity den-
sity (lower) as a function of radius. The black lines are
the measured values. Yellow and green lines correspond to
the modified profiles when assuming tidal radii of 43000
and
50500
respectively. Removing different “sheets” of light cor-
responds to different effects on the measured velocity disper-
sion.
7. DYNAMICAL MODELS
We aim to determine the mass distribution of the
galaxy that best fits both our spectroscopic and photo-
metric data. The distribution, in general, can be char-
acterized by the following equation:
ρ(r) =
M∗
L
ν(r) + ρDM (r) + MBHδ(0) (11)
where:
• ρ(r) is the matter density profile.
13. 13
Figure 11. χ2
distributions for every model. MODEL 1: every velocity data point included. MODEL 2: all but the central
and last M08 velocity bins included. MODEL 3: removed a sheet of “tidal light”, considered to be the stars outside a 43000
tidal
radius. MODEL 4: removed a sheet of “tidal light”, considered to be the stars outside a 50500
tidal radius. The first panels show
that none of the best fit models require a stellar M∗/L larger than ∼ 5.0. The second panels show that every model requires a
central black hole of mass ∼ 3.3 ± 2×106
M . The circular velocity is not at all well constrained in any of the models, although
there is a slight preference for values above 40 km s−1
in the ones that are not tidally corrected. The core radius rc is also poorly
constrained for all except Model 1, where a value of ∼1.7 kpc is favored, implying a flat central core. We sample vcir down to
10 km s−1
and for these plots we restrict the plot range around the most probable values in order to show the variations better.
14. 14
32 100 316
r(arcsec)
104
106
108
M(r)(M
)
MODEL 1
0 200 400 600
r(arcsec)
0.5
1.0
1.5
2.0
r
/
t
0 200 400 600
r(arcsec)
4
6
8
10
12
(km/s)
model
data
40 125 395
r(parsecs)
125 250 375 500 625
r(parsecs)
125 250 375 500 625
r(parsecs)
32 100 316
r(arcsec)
104
106
108
M(r)(M
)
MODEL 2
0 200 400 600
r(arcsec)
0.5
1.0
1.5
2.0
r
/
t
0 200 400 600
r(arcsec)
4
6
8
10
12
(km/s)
model
data
40 125 395
r(parsecs)
125 250 375 500 625
r(parsecs)
125 250 375 500 625
r(parsecs)
32 100 316
r(arcsec)
104
106
108
M(r)(M
)
MODEL 3
0 200 400 600
r(arcsec)
0.5
1.0
1.5
2.0
r
/
t
0 200 400 600
r(arcsec)
4
6
8
10
12
(km/s)
model
data
40 125 395
r(parsecs)
125 250 375 500 625
r(parsecs)
125 250 375 500 625
r(parsecs)
32 100 316
r(arcsec)
104
106
108
M(r)(M
)
MODEL 4
0 200 400 600
r(arcsec)
0.5
1.0
1.5
2.0
r
/
t
0 200 400 600
r(arcsec)
4
6
8
10
12
(km/s)
model
data
40 125 395
r(parsecs)
125 250 375 500 625
r(parsecs)
125 250 375 500 625
r(parsecs)
Figure 12. MODEL 1: every velocity data point included. MODEL 2: all but the central and last M08 velocity bins included.
MODEL 3: removed a sheet of “tidal light”, considered to be the stars outside a 43000
tidal radius. MODEL 4: removed a sheet
of “tidal light”, considered to be the stars outside a 50500
tidal radius. Left: enclosed mass vs. radius for black hole (green),
total (black), stellar (orange) and DM (blue). All the models with ∆χ2
< 1 are displayed in their respective color’s lighter
shade. Middle: velocity dispersion tensor anisotropy vs. radius. All the models with ∆χ2
< 1 are from the shaded region.
Right: velocity dispersion as a function of radius. All the models with ∆χ2
< 1 are in blue.
15. 15
• M∗
L is the stellar mass-to-light ratio, assumed con-
stant with radius.
• ν(r) is the deprojected luminosity density profile.
• ρDM (r) is the dark matter density profile.
• MBH is the black hole mass.
• δ(0) is a delta function at r = 0.
For the DM profile, we use a cored logarithmic poten-
tial, which translates to a dark matter density ρDM (r):
ρDM (r) =
v2
c
4πG
3r2
c + r2
(r2
c + r2)2
(12)
where vc is the asymptotic circular speed at r = ∞ and
rc the core radius. These profiles have a flat central core
of density ρc = 3v2
c /4πGr2
c for r . rc and an r−2
profile
for r > rc.
We use orbit-based models for the dynamical anal-
ysis. These orbit-based dynamical models where first
used by Schwarzschild (1979), with details in Gebhardt
et al. (2000); Thomas et al. (2004); Siopis et al. (2009).
The input to the models are the stellar luminosity den-
sity profile (which we describe in Section 3) and the
kinematics. The variables are the DM density profile’s
parameters, the stellar mass-to-light ratio and the black
hole mass. With a defined potential, we then generate
representative orbits and then find the weights of the or-
bits to best maximize the likelihood function fit to the
kinematics. We then modify the variables, re-run the
orbit library and fit, providing a χ2
for each parame-
ter set. After sampling the variables, we then produce
distribution of quality of fits. For each model, we run
approximately 20,000 stellar orbits, fitted to the 28 ve-
locity profiles. The velocity profiles come from the 23
VIRUS-W LOSVDs and the 5 LOSVDs generated from
the archival individual velocities at large radii. For the
black hole mass, we sample from 0 to 107
M , for the
stellar M/L we sample from 0.01 to 5, for the DM scale
radius we sample from 0 to 3kpc, and for the DM cir-
cular velocity we sample from 10–60 km s−1
. The exact
sampling within those ranges is discussed below. For the
light profile, we deproject the surface brightness profile
presented above. Since Leo I is already flattened with
an axis ratio of 0.8, we assume an edge-on configuration.
This deprojection is then unique, and we use the algo-
rithm as given in Gebhardt et al. (1996). All models are
run on the Texas Advanced Computation Center, and
we have approximately 30,000 models, where each one
takes about an hour on a single CPU.
7.1. DATA BINNING AND PARAMETER SPACE
SAMPLING
Due to the tidal and crowding issues raised in prior
sections we use both the VIRUS-W and M08 datasets,
replacing M08 with VIRUS-W data within 17800
, where
crowding is significant. The data are binned in a polar
grid of 20 radial bins and 5 angular bins. The VIRUS-
W data extend to 8000
, filling the polar bins as available,
whereas M08 data are divided into 5 radial bins (from
17800
to 66800
) to include sufficient fibers in each bin.
To deal with the possible effects of tidal disruption,
we arrange the data into four different configurations:
• MODEL 1: Considering all data above
• MODEL 2: Removing the last kinematic radial
bin
• MODEL 3: Removing a sheet of stars assuming
the tidal radius is at 43000
• MODEL 4: Removing a sheet of stars assuming
the tidal radius is at 50500
We will refer to these models in terms of their number
from here on.
When searching parameters that minimize χ2
we start
with a sparse grid search, which we combine with a Latin
hypercube for the initial sampling of the space. A Latin
hypercube randomly samples the space ensuring each
sample is the only one in each axis-aligned hyperplane
containing it, a method independent of the size of the
space. Subsequent minimization was carried out by a
constrained optimization using response surfaces with
radial basis functions as the response function. Briefly,
the algorithm uses radial basis functions to interpolate
over the samples. It further selects a new point that
both minimizes the interpolation and is farther away
than a given distance from any other point. With each
iteration, the given distance is modified to avoid getting
stuck in local minima. Details of the original algorithm
can be found in Knysh & Korkolis (2016).
7.2. RESULTS
Figure 11 shows the χ2
for models and all parameter
selections. In each figure, each point represents an indi-
vidual parameter selection. As reference, the red curve
is a convex hull that envelops the lower bound of the χ2
values. To define the best fit parameters and the uncer-
tainties, we use the red curve in that figure. We find the
∆χ2
= 1 from the model with the minimum value on
either side to define the 1-σ range, and take the mean
to represent the best-fit value. Table 3 presents these
values for each parameter and model.
16. 16
All models prefer a black hole of ∼ 3.3 ± 2×106
M .
Stellar mass-to-light ratios are poorly constrained, with
upper limits of ∼ 2 for the models without any tidal
corrections and ∼ 5 for the others, implying poorly con-
strained dynamical estimates for the stellar contribu-
tion. These are consistent with external constraints on
the total mass of Leo I from surface brightness and star
formation history studies (McConnachie 2012). The DM
halo parameters are the least constrained, having a ten-
dency for high circular velocities ∼ 50 km/s and core
radii closer to 1 kpc.
Figure 12 shows derived quantities for all parameter
selections within 1σ. Within these figures, the panels
represent total and stellar enclosed mass, anisotropy in
the velocity dispersion, and projected velocity disper-
sion as a function of radius. We quantify the anisotropy
in the velocity dispersion tensor with σr/σt, the ratio
of radial to tangential anisotropy in the galaxy. The
tangential anisotropy σt is defined as
σt ≡
r
1
2
(σ2
θ + σ2
φ + ν2
φ) (13)
where νφ is the rotational velocity (streaming motions
in r and θ are assumed to be zero).
Overall, the truncated models contain close to half of
the enclosed mass of the non-truncated ones, the latter
having an enclosed mass of ∼ 108
M . For Models 1
and 2, which do not take into account tidal effects, the
anisotropy shows large variations, such that the stars
arrange themselves on orbits that start isotropic, then
become extremely radial, and end up isotropic as a func-
tion of radius. Whereas models including tidal effects
have smoothly varying anisotropy profiles. The model
with the most modest tidal effects, Model 4, is nearly
isotropic throughout the galaxy.
The rightmost panels in Figure 12 show the projected
velocity dispersion profiles as a function of radius for
data and models. For the blue points that represent the
models, we include all models that are within ∆χ2
= 1
deviation from the best fit. The variation in projected
dispersion is very small for this set, as can be seen in the
figure. The models represent the kinematic data well in
nearly all regions.
Figure 13 shows the dynamical M/L ratio vs. loga-
rithmic radius for the four assumed models. It is clear
that the central kinematics are dominated by the black
hole, and the variation between models is minimal for
that region. The largest variation between models hap-
pens between 10000
and 20000
, which is the region where
the stellar component dominates. At larger radius, the
M/L values rise due to the inclusion of the dark halo
when using the full datasets (Model 1 or 2). For the
models with a tidal radius, the M/L at large radii is
consistent with being constant.
Overall, the most robust prediction is that of the black
hole mass. For the adopted cored logarithmic DM pro-
file, the various assumptions for the tidal effects do not
influence the estimates, ranging from 3.2 ± 2.2×106
M
to 3.8±3.0×106
M . Table 3 summarizes all the results
for the different models discussed above.
101 102
0
250
500
750
1000
1250
1500
M
dyn
/L(M
/L
)
MODEL 3
MODEL 4
101 102
r(arcsec)
100
101
102
103
M
dyn
/L(M
/L
)
MODEL 1
MODEL 2
MODEL 3
MODEL 4
Figure 13. Derived dynamical M/L vs radius for the vari-
ous models in log scale. Regardless of tidal radius and kine-
matical assumptions, the kinematics of the central region of
the galaxy are dominated by the black hole. The presence of
a relatively low amount of DM is required only in the outer
regions of the galaxy. In the 10
− 20
radial region, a typical
stellar population M/L is adequate to fit the models.
7.3. Central Mass Density Profile
To investigate whether the black hole mass is influ-
enced by the assumed DM potential, we also run dark
matter models that have a central density increase. A
standard model of the dark matter profile, especially for
systems without significant influence from baryonic pro-
cesses, is one defined by Navarro et al. (1997) (NFW).
This model has a central density rise compared to the
cored profile that we use as default. The NFW profile is
defined by two parameters, the concentration c and the
scale radius Rs.
We run NFW models for Model 1, where we include all
kinematic observations. This comparison will be repre-
sentative of potential changes. We sample concentration
indices from 3 to 60, and scale radii from 0.1 to 20 kpc,
17. 17
Table 3. Leo I best fit density parameters
Model Description M∗
L MBH vcir rc
M300
dyn
L ∆χ2
NO BH M300
∗ M300
DM
[M
L ] [106
M ] [km
s ] [kpc] [M
L ] [106
M ] [106
M ]
(1) (2) (3) (4) (5) (6) (7) (8) (9) (10)
1 All data < 1.8 3.3 ± 1.8 > 34.5 1.5 ± 0.6 2.6 ± 0.3 13.8 4.2 ± 4.1 7.5 ± 1.9
2 R< 50000
< 1.8 3.5 ± 1.9 > 34.8 1.4 ± 0.5 2.6 ± 0.3 10.3 3.3 ± 3.3 7.9 ± 1.4
3 rtidal = 43000
< 4.1 3.2 ± 2.2 − > 0.6 3.2 ± 0.4 7.1 9.9 ± 9.9 5.9 ± 5.6
4 rtidal = 50500
< 4.7 3.8 ± 3.0 − > 0.48 4.0 ± 0.4 6.4 12.0 ± 12.0 7.7 ± 7.3
c rs[kpc]
5 NFW 0.7 ± 0.5 2.1 ± 1.6 7.0 ± 3.2 > 5.6 2.3 ± 0.3 14.3 3.0 ± 1.9 13.8 ± 1.0
Note—The best fit values extracted from fig. 11. Errors are from a ∆χ2
= 1. When the errors extended further
than the surveyed range we included inequality signs. Unconstrained parameters are indicated with a dash. Column
(1): model name. Column (2): model description. Column (3): stellar mass-to-light ratio. Column (4): black hole
mass. Columns (5) and (6): circular velocity and core radius for Models 1 through 4 and the NFW concentration
parameter and scale radius for Model 5. Column (7): dynamical M/L inside 300 pc. Column (8): difference in χ2
between the best solution including a black hole and that without one. Columns (9) and (10): the enclosed stellar
mass and DM mass at 300 pc.
including similar ranges in black hole mass and stellar
M/L as when using the core logarithmic potential. The
best-fitted black hole mass is (2.1±1.6)×106
M , stellar
M/L is 0.7 ± 0.5, c is 7.0 ± 3.2, and scale radius & 5.6
kpc. Figure 14 presents the results.
The overall fit to the kinematic data is worse for the
NFW profile compared to the cored logarithmic profile.
The best-fit black hole mass from the NFW profile is
lower but consistent with the value obtained from the
logarithmic profile. The change in χ2
between the model
with no black hole and the best-fitted black hole is 14,
which is a higher difference than that measured in the
other models. Thus, the black hole mass is preferred
at a stronger level with the NFW profile. The stellar
M/L is even smaller, making the contribution to the
potential from the stars even less important. Since the
overall fit is worse and the stellar M/L is pushed into an
even more unrealistic regime, the NFW profile does not
appear to be a good representation of the density profile
for Leo I. We adopt the cored logarithmic profile as the
model that best represents the dark matter contribution
for Leo I.
A value of 7 for the concentration parameter preferred
by the NFW models is atypical for a dwarf spheroidal
galaxy, with a value ∼ 15 being more typical in the liter-
ature (Dutton & Macciò 2014; Ludlow et al. 2014). If we
restrict to only these higher concentration parameters
(c > 12), the inferred black hole mass remains roughly
constant at 2 × 106
M , and the χ2
increases. In the
extreme NFW case of c > 50, the black hole mass un-
certainty increases to include low masses, but the model
becomes unrealistic with a large χ2
. For comparison, re-
stricting to a smaller core radius in the cored logarithmic
profile rc < 1 kpc, changes ∆χ2
by a small amount and
similarly leaves the black hole mass unaffected. Thus,
using either a more standard NFW profile or the one
found here, the significance of requiring a black hole re-
mains the same.
8. DISCUSSION
The two main conclusions of this work are that we find
a central black hole mass of ∼ 3.3 ± 2×106
M , and a
dark halo profile that is much more uncertain compared
to previous studies. A black hole mass this large in Leo I
is significant in many respects. It is the first detection
of a black hole in a dwarf spheroidal using spatially-
resolved kinematics, it has a mass that is similar to the
total stellar mass of the system, and it is a comparable
mass to that of the black hole in the center of the Milky
Way. While the uncertainty on the mass is large, the
no-black-hole models are significantly ruled out. Given
the implications of a such a result, we discuss caveats
and potential concerns regarding the robustness of the
black hole mass measurement.
18. 18
Figure 14. χ2
distributions for a model taking an NFW
dark matter profile. The top-left panel is the stellar M/L.
Top-right is the black hole mass. Bottom-left is the NFW
concentration parameter. Bottom-right is the NFW scale
radius.
We first describe the caveat that these results are ob-
viously dependent on the various mass profiles we have
assumed. The dynamical models rely on a tracer popula-
tion (i.e., the stars) that are only responsive to the over-
all gravitational potential. The most robust method for
determining the mass density profile is using a technique
without reliance on parametric models. One example is
given in Jardel & Gebhardt (2013) where they deter-
mine the mass density profile in radial bins. With the
mass density profiles measured one can then fit various
models to those profiles to split it into individual com-
ponents. This brute force method is impractical given
our compute resources. For this paper, we apply the
more traditional approach where we parameterize the
mass density profile. We use four parameters charac-
terizing a black hole, a two-component dark halo and a
stellar component, under two different suites of models.
Thus, the robust result is the underlying sum of these
three components. For the individual components there
can be degeneracies of the parameters. An obvious de-
generacy is between the stellar mass-to-light ratio and
the DM profile. We have explored this specific degen-
eracy by studying the models that have mass-to-light
ratios typical for these stars, where the stellar popula-
tions models suggest values around 2. The results for the
black hole mass change little, and well within the 68%
confidence band for the black hole mass, when restrict-
ing the range of the stellar mass-to-light ratio. Thus,
even if we force the stellar mass-to-light ratio to a stan-
dard value, we would measure the same black hole mass.
For the black hole mass, the results are the most robust
since our kinematics are well measured in the central
regions. If either the stars or the DM were to mimic the
effect of a black hole, it would require an unrealistically
steep central density profile.
The nearly constant velocity dispersion within 20000
at around 12 km s−1
, and in particular the central value
at 1500
, is the primary driver for a model preference of a
central black hole. The central kinematic point will have
the most influence, and all models we have run include
that point. Since all of the VIRUS-W data are treated
in the same manner through this analysis and have simi-
lar signal-to-noise ratio, we always include all VIRUS-W
data. Furthermore, the large sphere of influence due to
this large black hole mass includes all of the VIRUS-
W kinematics. Since we have a full suite of parameters
for the DM profile, we can explore those parameter re-
gions that are more typical for dSphs and study poten-
tial changes in the black hole mass with different dark
halo properties. We find very consistent values for the
black hole mass under a large variety of dark halo prop-
erties, which includes those parameters that have tra-
ditionally been used for dwarf spheroidals. Only when
going to extreme models where the NFW concentration
is above 50 do the χ2
contours extend to lower masses, at
the expense of a very poor fit compared to our preferred
model. The reason is that we have such high signal-to-
noise kinematics in the central region, where the black
hole has the most influence. The sphere of influence
of the black hole is commonly used as an approximate
radius that one needs to spatially resolve for a robust
estimate. This radius is where the mass of the black
hole is equal to the stellar mass or dark matter mass,
which ranges from 125–250 pc or 10000
–20000
. Within
these radii, we have our highest quality data.
The expectation from a model with no black hole and
the light profile of Leo I is to have the velocity disper-
sion decrease towards the center. The kinematics pub-
lished by (Mateo et al. 2008) do in fact show a decrease,
and we argue in Section 5 that decrease they measure
is due to not considering effects of crowding. Crowd-
ing effects are easily understood and must be present at
some level. When we correct for crowding, we recover
an increase in the central velocity dispersion. The ad-
ditional kinematic information comes from our VIRUS-
W observations using integrated light. The integrated-
light kinematics naturally do not suffer from crowding
effects. Getting consistent results for the velocity dis-
19. 19
persion from either correcting the individual stellar kine-
matic or the integrated-light kinematics provides greater
confidence in the stellar velocity dispersion profile. This
profile is clearly the key to determining the central kine-
matics. It is important that all dwarf spheroidal kine-
matics be re-evaluated for crowding effects in the central
regions.
The no-black-hole models have ∆χ2
from the best fit
model that range from 6.4 to13.8, formally excluding the
no-black-hole case at over 95% confidence. These ∆χ2
are similar to many of the published black hole models
in normal galaxies (e.g. Erwin et al. 2018). While we
use dynamical models with a nonparametric orbital dis-
tribution, additional tests could include triaxiality and
nonequilibrium dynamical effects. These additional con-
siderations should have a small effect on the mass of the
black hole, given the large ∆χ2
. The large ratio of the
black hole mass to the host galaxy mass has been de-
tected previously in other galaxies, with values ranging
from 5–25% of the galaxy mass being in the black hole
for some systems. Ahn et al. 2017 find a black hole of
13% of the galaxy mass in vucd3 and 18% in M59c0;
Yıldırım et al. 2015 find 5% in NGC1277 and Walsh
et al. 2017 find 1% in Mrk1216, while den Brok et al.
2015 find 10% in NGC4395. The typical value from the
full sample of published masses is 0.15% (Viero et al.
2014). For Leo I, the relative mass of the black hole to
the host depends on the radial extent one uses to define
Leo I. Over the four models presented, within 300 pc
(a standard unit used for these systems), the black hole
mass ranges from 16-22% of the total mass. This per-
centage decreases as one considers the full mass of the
system, going down to 3% for the most extended model.
Thus, the black hole mass relative to the host mass is
consistent with the other extreme systems reported.
A black hole mass this large in Leo I is not expected
from extrapolation of any of the standard black-hole to
host-galaxy correlations. Of course, these small systems
do not necessarily need to follow the trends seen in nor-
mal galaxies, but the black hole mass reported here does
stand out. Lützgendorf et al. (2015) explore extrapola-
tions of black hole correlations down to globular cluster
scales, and using a velocity dispersion of 12 km s−1
,
Leo I has a black hole mass a factor of 100 more than
the extrapolated trends. On the numerical side, van
Wassenhove et al. 2010 consider different scenarios for
formation of a black hole in Milky Way satellites and
place the likelihood of one of them having a black hole
around the size found here to be below 1%, but this
result also depends on the initial seed mass (see also
Bellovary et al. 2021). Runaway mergers of stellar mass
black holes are unlikely to produce such a black hole
in such a small galaxy, since the required initial mass
function to reach the ratios seen in the models might
be more top-heavy than what chemical abundances and
star formation history studies suggest. An alternative
explanation for the abnormally large central black hole
may come from the recent study of Leo I’s star formation
history from Ruiz-Lara et al. 2020. The authors iden-
tify a period of quenching from z = 1 − 2 followed by
re-ignition until almost present day when ram-pressure
stripping may have shut it down as it fell into the Milky
Way. While the authors speculate this re-ignition at in-
termediate redshifts could be due to a past merger with
a smaller dwarf this could also be consistent with gas
accretion and potential active galactic nuclei feedback,
lending support to the high MBH values presented here.
Amaro-Seoane et al. 2014 also suggest that dwarf sys-
tems may in fact have significantly larger black holes
compared to the host-galaxy black-hole relationships.
Having a larger sample of black holes limits measured
in dwarf galaxies will be important to explore.
There are alternatives to a central black hole as de-
rived from the observed kinematics. The first is a collec-
tion of dark remnants as opposed to a black hole (Zocchi
et al. 2018; Aros et al. 2020). In this case, a central con-
centration of remnants implies two unlikely ingredients:
(a) an extremely top-heavy initial mass function in order
to produce the number of remnants necessary to match
the detected dark mass, and (b) a small two-body relax-
ation time in order to get enough remnants into the cen-
tral region. For Leo I, the very low stellar density makes
both unlikely, although detailed evolutionary models are
warranted. The second is having a significant number
of binary stars that increase the measured velocity dis-
persion. As shown in Spencer et al. 2017, the change
in measured dispersion is small even for a large binary
fraction of 50%. Thus the change of the measured cen-
tral dispersion in Leo I of 12 km s−1
would be minimal,
especially out to 10000
, and will have negligible effect on
the measured black hole mass.
Regarding the dark halo, the best-fit logarithmic pro-
file models have circular velocities that range from 30-
60 km s−1
, but are unconstrained at the upper limit.
This range is larger than previous uncertainty estimates.
The reasons for the large range include allowing more
freedom in the dynamical models and including a range
of tidal assumptions. Having a circular velocity at the
higher limit of 60 km s−1
will significantly help with the
“too big to fail” problem (Boylan-Kolchin et al. 2011),
as it implies these systems actually exist. Having a cir-
cular velocity at the lower limit of 30 km s−1
makes the
dark halo barely significant.
20. 20
Furthermore, the internal velocity anisotropies (as
presented in Figure 11) show large radial variation for
the non-truncated models. The anisotropy profiles for
the truncated models are much smoother, and in par-
ticular Model 4 is consistent with an isotropic distribu-
tion. Comparing to systems supported by dispersion,
most show nearly isotropic orbits at large radii (Geb-
hardt et al. 2003), implying the truncated models are
more realistic than the non-truncated models. The rel-
ative amount of dark matter in the truncated models is
much less than for the non-truncated models. Thus, the
need for dark matter is even less given the anisotropy
profiles.
The assumption of a cored or NFW dark matter model
has little effect on the black hole’s presence, although the
NFW profile does prefer a lower mass (2 ± 1) × 106
M ,
rather than 3.3±2×106
M . The change in χ2
between
the model with no black hole and the best fit model is ac-
tually larger for the NFW profile. Thus, the NFW model
provides slightly stronger implications for the presence
of a black hole. The NFW model is a slightly worse fit
overall, and we prefer the cored logarithmic profiles.
The strongest statement we can make from this anal-
ysis regarding the dark halo in Leo I is that it is very
uncertain and can accommodate large differences in in-
terpretation. In fact, the most realistic models (i.e., the
truncated models) have a very weak need for a dark
matter halo. Regarding the black hole mass, we have
explored the models and assumptions in a variety of
ways, and the significance of the black hole mass re-
mains strong. It is worthwhile to continue studying
dwarf spheroidals using robust and general dynamical
models.
9. ACKNOWLEDGMENTS
We are grateful for the excellent and extensive com-
ments from the referee, which significantly improved
this work. EN and KG worked with the support
by the National Science Foundation under Grant No.
1616452. Some of the data presented in this paper are
obtained from the Mikulski Archive for Space Telescopes
(MAST).
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