Exploring the nature and synchronicity of early cluster formation in the Large Magellanic Cloud – II. Relative ages and distances for six ancient globular clusters
We analyse Hubble Space Telescope observations of six globular clusters in the Large Magel- lanic Cloud (LMC) from programme GO-14164 in Cycle 23. These are the deepest available observations of the LMC globular cluster population; their uniformity facilitates a precise comparison with globular clusters in the Milky Way. Measuring the magnitude of the main- sequence turn-off point relative to template Galactic globular clusters allows the relative ages of the clusters to be determined with a mean precision of 8.4 per cent, and down to 6 per cent for individual objects. We find that the mean age of our LMC cluster ensemble is identical to the mean age of the oldest metal-poor clusters in the Milky Way halo to 0.2 ± 0.4 Gyr. This provides the most sensitive test to date of the synchronicity of the earliest epoch of globular cluster formation in two independent galaxies. Horizontal branch magnitudes and subdwarf fitting to the main sequence allow us to determine distance estimates for each cluster and examine their geometric distribution in the LMC. Using two different methods, we find an average distance to the LMC of 18.52 ± 0.05.
Hubble Space Telescope Observations of NGC 253 Dwarf Satellites: Three Ultra-...Sérgio Sacani
We present deep Hubble Space Telescope (HST) imaging of five faint dwarf galaxies associated with the nearby
spiral NGC 253 (D ≈ 3.5 Mpc). Three of these are newly discovered dwarf galaxies, while all five were found in
the Panoramic Imaging Survey of Centaurus and Sculptor, a Magellan+Megacam survey to identify faint dwarfs
and other substructures in resolved stellar light around massive galaxies outside of the Local Group. Our HST data
reach 3 magnitudes below the tip of the red giant branch for each dwarf, allowing us to derive their distances,
structural parameters, and luminosities. All five systems contain mostly old, metal-poor stellar populations
(age ∼12 Gyr, [M/H] −1.5) and have sizes (rh ∼ 110–3000 pc) and luminosities (MV ∼ −7 to −12 mag) largely
consistent with Local Group dwarfs. The three new NGC 253 satellites are among the faintest systems discovered
beyond the Local Group. We also use archival H I data to place limits on the gas content of our discoveries. Deep
imaging surveys such as our program around NGC 253 promise to elucidate the faint end of the satellite luminosity
function and its scatter across a range of galaxy masses, morphologies, and environments in the decade to come
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 three-dimensional map of the Milky Way using 66,000 Mira variable starsSérgio Sacani
We study the three-dimensional structure of the Milky Way using 65,981 Mira variable stars discovered
by the Optical Gravitational Lensing Experiment (OGLE) survey. The spatial distribution of the Mira
stars is analyzed with a model containing three barred components that include the X-shaped boxy
component in the Galactic center (GC), and an axisymmetric disk. We take into account the distance
uncertainties by implementing the Bayesian hierarchical inference method. The distance to the GC is
R0 = 7.66 ± 0.01(stat.) ± 0.39(sys.) kpc, while the inclination of the major axis of the bulge to the
Sun-GC line-of-sight is θ = 20.2
◦ ± 0.6
◦
(stat.) ± 0.7
◦
(sys.). We present, for the first time, a detailed
three-dimensional map of the Milky Way composed of young and intermediate-age stellar populations.
Our analysis provides independent evidence for both the X-shaped bulge component and the flaring
disk (being plausibly warped). We provide the complete dataset of properties of Miras that were used
for calculations in this work. The table includes: mean brightness and amplitudes in nine photometric
bands (covering a range of wavelength from 0.5 to 12 µm), photometric chemical type, estimated
extinction, and calculated distance with its uncertainty for each Mira variable. The median distance
accuracy to a Mira star is at the level of 6.6%.
Hubble Space Telescope Observations of NGC 253 Dwarf Satellites: Three Ultra-...Sérgio Sacani
We present deep Hubble Space Telescope (HST) imaging of five faint dwarf galaxies associated with the nearby
spiral NGC 253 (D ≈ 3.5 Mpc). Three of these are newly discovered dwarf galaxies, while all five were found in
the Panoramic Imaging Survey of Centaurus and Sculptor, a Magellan+Megacam survey to identify faint dwarfs
and other substructures in resolved stellar light around massive galaxies outside of the Local Group. Our HST data
reach 3 magnitudes below the tip of the red giant branch for each dwarf, allowing us to derive their distances,
structural parameters, and luminosities. All five systems contain mostly old, metal-poor stellar populations
(age ∼12 Gyr, [M/H] −1.5) and have sizes (rh ∼ 110–3000 pc) and luminosities (MV ∼ −7 to −12 mag) largely
consistent with Local Group dwarfs. The three new NGC 253 satellites are among the faintest systems discovered
beyond the Local Group. We also use archival H I data to place limits on the gas content of our discoveries. Deep
imaging surveys such as our program around NGC 253 promise to elucidate the faint end of the satellite luminosity
function and its scatter across a range of galaxy masses, morphologies, and environments in the decade to come
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 three-dimensional map of the Milky Way using 66,000 Mira variable starsSérgio Sacani
We study the three-dimensional structure of the Milky Way using 65,981 Mira variable stars discovered
by the Optical Gravitational Lensing Experiment (OGLE) survey. The spatial distribution of the Mira
stars is analyzed with a model containing three barred components that include the X-shaped boxy
component in the Galactic center (GC), and an axisymmetric disk. We take into account the distance
uncertainties by implementing the Bayesian hierarchical inference method. The distance to the GC is
R0 = 7.66 ± 0.01(stat.) ± 0.39(sys.) kpc, while the inclination of the major axis of the bulge to the
Sun-GC line-of-sight is θ = 20.2
◦ ± 0.6
◦
(stat.) ± 0.7
◦
(sys.). We present, for the first time, a detailed
three-dimensional map of the Milky Way composed of young and intermediate-age stellar populations.
Our analysis provides independent evidence for both the X-shaped bulge component and the flaring
disk (being plausibly warped). We provide the complete dataset of properties of Miras that were used
for calculations in this work. The table includes: mean brightness and amplitudes in nine photometric
bands (covering a range of wavelength from 0.5 to 12 µm), photometric chemical type, estimated
extinction, and calculated distance with its uncertainty for each Mira variable. The median distance
accuracy to a Mira star is at the level of 6.6%.
Prospects for Detecting Gaps in Globular Cluster Stellar Streams in External ...Sérgio Sacani
Stellar streams form through the tidal disruption of satellite galaxies or globular clusters orbiting a
host galaxy. Globular cluster streams are exciting since they are thin (dynamically cold) and, therefore
sensitive to perturbations from low-mass subhalos. Since the subhalo mass function differs depending
on the dark matter composition, these gaps can provide unique constraints on dark matter models.
However, current samples are limited to the Milky Way. With its large field of view, deep imaging
sensitivity, and high angular resolution, the upcoming Nancy Grace Roman Space Telescope (Roman)
presents a unique opportunity to increase the number of observed streams and gaps significantly. This
paper presents a first exploration of the prospects for detecting gaps in streams in M31 and other
nearby galaxies with resolved stars. We simulate the formation of gaps in a Palomar-5-like stream
and generate mock observations of these gaps with background stars in M31 and the foreground Milky
Way stellar fields. We assess Roman’s ability to detect gaps out to 10 Mpc through visual inspection
and with the gap-finding tool FindTheGap. We conclude that gaps of ≈ 1.5 kpc in streams that are
created from subhalos of masses ≥ 5×106 M⊙ are detectable within a 2–3 Mpc volume in exposures of
1000s–1 hour. This volume contains ≈ 150 galaxies, including ≈ 8 galaxies with luminosities > 109 L⊙.
Large samples of stream gaps in external galaxies will open up a new era of statistical analyses of gap
characteristics in stellar streams and help constrain dark matter models.
Stellar-mass black holes in the Hyades star cluster?Sérgio Sacani
Astrophysical models of binary-black hole mergers in the Universe require a significant fraction of stellar-mass black holes (BHs)
to receive negligible natal kicks to explain the gravitational wave detections. This implies that BHs should be retained even in
open clusters with low escape velocities (≲ 1 km/s). We search for signatures of the presence of BHs in the nearest open cluster
to the Sun – the Hyades – by comparing density profiles of direct 𝑁-body models to data from Gaia. The observations are best
reproduced by models with 2−3 BHs at present. Models that never possessed BHs have an half-mass radius ∼ 30% smaller than
the observed value, while those where the last BHs were ejected recently (≲ 150 Myr ago) can still reproduce the density profile.
In 50% of the models hosting BHs, we find BHs with stellar companion(s). Their period distribution peaks at ∼ 103 yr, making
them unlikely to be found through velocity variations. We look for potential BH companions through large Gaia astrometric and
spectroscopic errors, identifying 56 binary candidates - none of which consistent with a massive compact companion. Models
with 2 − 3 BHs have an elevated central velocity dispersion, but observations can not yet discriminate. We conclude that the
present-day structure of the Hyades requires a significant fraction of BHs to receive natal kicks smaller than the escape velocity
of ∼ 3 km s−1
at the time of BH formation and that the nearest BHs to the Sun are in, or near, Hyades.
A giant thin stellar stream in the Coma Galaxy ClusterSérgio Sacani
The study of dynamically cold stellar streams reveals information about the gravitational potential where they reside and provides
important constraints on the properties of dark matter. However, the intrinsic faintness of these streams makes their detection beyond
Local environments highly challenging. Here, we report the detection of an extremely faint stellar stream (µg,max = 29.5 mag arcsec−2
)
with an extraordinarily coherent and thin morphology in the Coma Galaxy Cluster. This Giant Coma Stream spans ∼510 kpc in length
and appears as a free-floating structure located at a projected distance of 0.8 Mpc from the center of Coma. We do not identify any
potential galaxy remnant or core, and the stream structure appears featureless in our data. We interpret the Giant Coma Stream as
being a recently accreted, tidally disrupting passive dwarf. Using the Illustris-TNG50 simulation, we identify a case with similar
characteristics, showing that, although rare, these types of streams are predicted to exist in Λ-CDM. Our work unveils the presence
of free-floating, extremely faint and thin stellar streams in galaxy clusters, widening the environmental context in which these objects
are found ahead of their promising future application in the study of the properties of dark matter.
The fornax deep_survey_with_vst_i_the_extended_and_diffuse_stellar_halo_of_ng...Sérgio Sacani
We have started a new deep, multi-imaging survey of the Fornax cluster, dubbed Fornax Deep
Survey (FDS), at the VLT Survey Telescope. In this paper we present the deep photometry inside
two square degrees around the bright galaxy NGC 1399 in the core of the cluster. We found that
the core of the Fornax cluster is characterised by a very extended and diffuse envelope surrounding
the luminous galaxy NGC 1399: we map the surface brightness out to 33 arcmin (∼ 192 kpc)
from the galaxy center and down to μg ∼ 31 mag arcsec−2 in the g band. The deep photometry
allows us to detect a faint stellar bridge in the intracluster region on the west side of NGC 1399
and towards NGC 1387. By analyzing the integrated colors of this feature, we argue that it
could be due to the ongoing interaction between the two galaxies, where the outer envelope of
NGC 1387 on its east side is stripped away. By fitting the light profile, we found that exists a
physical break radius in the total light distribution at R = 10 arcmin (∼ 58 kpc) that sets the
transition region between the bright central galaxy and the outer exponential halo, and that the
stellar halo contributes for 60% of the total light of the galaxy (Sec. 3.5). We discuss the main
implications of this work on the build-up of the stellar halo at the center of the Fornax cluster.
By comparing with the numerical simulations of the stellar halo formation for the most massive
BCGs (i.e. 13 < logM200/M⊙ < 14), we find that the observed stellar halo mass fraction is
consistent with a halo formed through the multiple accretion of progenitors with stellar mass in
the range 108 − 1011 M⊙. This might suggest that the halo of NGC 1399 has also gone through
a major merging event. The absence of a significant number of luminous stellar streams and
tidal tails out to 192 kpc suggests that the epoch of this strong interaction goes back to an early
formation epoch. Therefore, differently from the Virgo cluster, the extended stellar halo around
NGC 1399 is characterised by a more diffuse and well-mixed component, including the ICL.
The vvv survey_reveals_classical_cepheids_tracing_a_young_and_thin_stellar_di...Sérgio Sacani
Com o auxílio do telescópio VISTA instalado no Observatório do Paranal do ESO, astrônomos descobriram uma componente anteriormente desconhecida da Via Láctea. Ao mapear a localização de uma classe de estrelas que variam em brilho chamadas Cefeidas, foi descoberto um disco de estrelas jovens enterradas por trás de espessas nuvens de poeira no bojo central.
O rastreio público do ESO VISTA Variables in the Vía Láctea (VVV) [1] usa o telescópio VISTA instalado no Observatório do Paranal para obter imagens múltiplas em épocas diferentes das regiões centrais da nossa Galáxia nos comprimentos de onda do infravermelho [2]. O rastreio está descobrindo uma enorme quantidade de novos objetos, incluindo estrelas variáveis, aglomerados e estrelas em explosão (eso1101, eso1128, eso1141).
Uma equipe de astrônomos, liderada por Istvan Dékány da Pontificia Universidad Católica de Chile, utilizou dados deste rastreio, obtidos entre 2010 e 2014, para fazer uma descoberta notável — um componente anteriormente desconhecido da Via Láctea, a Galáxia que nos acolhe.
JWST early Universe observations and 𝚲CDM cosmologySérgio Sacani
Deep space observations of the James Webb Space Telescope (JWST) have revealed that the structure and
masses of very early Universe galaxies at high redshifts (𝑧~15), existing at ~0.3 Gyr after the BigBang,
may be as evolved as the galaxies in existence for ~10 Gyr. The JWST findings are thus in strong tension
with the ΛCDM cosmological model. While tired light (TL) models have been shown to comply with the
JWST angular galaxy size data, they cannot satisfactorily explain isotropy of the cosmic microwave
background (CMB) observations or fit the supernovae distance modulus vs. redshift data well. We have
developed hybrid models that include the tired light concept in the expanding universe. The hybrid ΛCDM
model fits the supernovae type 1a data well but not the JWST observations. We present a model with
covarying coupling constants (CCC), starting from the modified FLRW metric and resulting Einstein and
Friedmann equations, and a CCC+TL hybrid model. They fit the Pantheon+ data admirably, and the
CCC+TL model is compliant with the JWST observations. It stretches the age of the universe to 26.7 Gyr
with 5.8 Gyr at 𝑧 = 10 and 3.5 Gyr at 𝑧 = 20, giving enough time to form massive galaxies. It thus
resolves the 'impossible early galaxy' problem without requiring the existence of primordial black hole
seeds or modified power spectrum, rapid formation of massive population III stars, and super Eddington
accretion rates. One could infer the CCC model as an extension of the ΛCDM model with a dynamic
cosmological constant.
Detection of anisotropic satellite quenching in galaxy clusters up to z ∼ 1Sérgio Sacani
Satellite galaxies in the cluster environment are more likely to be quenched than galaxies in the general field. Recently, it has
been reported that satellite galaxy quenching depends on the orientation relative to their central galaxies: satellites along the
major axis of centrals are more likely to be quenched than those along the minor axis. In this paper, we report a detection
of such anisotropic quenching up to z ∼ 1 based on a large optically selected cluster catalogue constructed from the Hyper
Suprime-Cam Subaru Strategic Program. We calculate the quiescent satellite galaxy fraction as a function of orientation angle
measured from the major axis of central galaxies and find that the quiescent fractions at 0.25 < z < 1 are reasonably fitted
by sinusoidal functions with amplitudes of a few per cent. Anisotropy is clearer in inner regions (<r200m) of clusters and not
significant in cluster outskirts (>r200m). We also confirm that the observed anisotropy cannot be explained by differences in
local galaxy density or stellar mass distribution along the two axes. Quiescent fraction excesses between the two axes suggest
that the quenching efficiency contributing to the anisotropy is almost independent of stellar mass, at least down to our stellar
mass limit of M∗ = 1 × 1010 M. Finally, we argue that the physical origins of the observed anisotropy should have shorter
quenching time-scales than ∼ 1 Gyr, like ram-pressure stripping, because, for anisotropic quenching to be observed, satellites
must be quenched before their initial orientation angles are significantly changed.
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 physical conditions_in_a_pre_super_star_cluster_molecular_cloud_in_the_an...Sérgio Sacani
Artigo descreve estudo feitos pelos astrônomos utilizando o ALMA para descobrir um proto-aglomerado globular de estrelas gigantes se formando no interior das galáxias Antenas, o famoso par de galáxias em interação. É a primeira vez que os astrônomos conseguem observar um objeto desse tipo nos seus estágios iniciais de vida e com o ambiente ao redor inalterado.
The gaia eso_survey_stellar_content_and_elemental_abundances_in_the_massive_c...Sérgio Sacani
Estudo sobre o conteúdo estelar e os elementos que estão presentes no aglomerado estelar aberto NGC 6705, também conhecido como Aglomerado do Pato Selvagem.
Os astrônomos descobriram um processo único sobre como as maiores galáxias elípticas do universo continuam gerando estrelas muito tempo depois do anos de pico de nascimentos estelares. A alta resolução e a sensibilidade à radiação ultravioleta do Hubble, permitiu aos astrônomos observarem nós brilhantes de estrelas azuis, quentes, se formando juntamente com jatos de buracos negros ativos encontrados nos centros das gigantescas galáxias elípticas.
Combinando dados do Huubble com observações feitas por um conjunto de telescópios baseados tanto em Terra como no espaço, duas equipes independentes descobriram que os jatos dos buracos negros, e as estrelas recém-nascidas são todos partes de um ciclo auto-regulado. Jatos de alta energia atirados do buraco negro aquecem um halo de gás circulante, controlando a taxa com a qual o gás esfria e cai na galáxia.
“Pense no gás ao redor da galáxia como uma atmosfera”, explicou o líder do primeiro estudo, Megan Donahue, da Universidade Estadual do Michigan. “Essa atmosfera pode conter material em diferentes estados, do mesmo modo que a nossa atmosfera tem gás, nuvens e chuva. O que nós estamos vendo é um processo parecido com uma tempestade. À medida que os jatos impulsionam o gás para fora do centro da galáxia, parte do gás esfria e precipita em aglomerados frios que caem de volta para o centro da galáxia como gotas de chuvas”.
“As gotas de chuva eventualmente esfriam o suficiente para tornar-se nuvens de formação de estrelas de gás frio molecular, e a capacidade de observar no ultravioleta distante do Hubble, nos permitiu observar diretamente esses chuviscos de formação de estrelas”, explicou o líder do segundo estudo, Grant Tremblay, da Universidade de Yale. “Nós sabemos que esses chuviscos estão linkados com os jatos, pois eles foram encontrados em filamentos que se dobram ao redor dos jatos, ou abraçam as bordas de bolhas gigantes que os jatos inflaram”, disse Tremblay. “E eles terminam fazendo um redemoinho de gás de formação de estrelas ao redor do buraco negro central”.
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.
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.
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Prospects for Detecting Gaps in Globular Cluster Stellar Streams in External ...Sérgio Sacani
Stellar streams form through the tidal disruption of satellite galaxies or globular clusters orbiting a
host galaxy. Globular cluster streams are exciting since they are thin (dynamically cold) and, therefore
sensitive to perturbations from low-mass subhalos. Since the subhalo mass function differs depending
on the dark matter composition, these gaps can provide unique constraints on dark matter models.
However, current samples are limited to the Milky Way. With its large field of view, deep imaging
sensitivity, and high angular resolution, the upcoming Nancy Grace Roman Space Telescope (Roman)
presents a unique opportunity to increase the number of observed streams and gaps significantly. This
paper presents a first exploration of the prospects for detecting gaps in streams in M31 and other
nearby galaxies with resolved stars. We simulate the formation of gaps in a Palomar-5-like stream
and generate mock observations of these gaps with background stars in M31 and the foreground Milky
Way stellar fields. We assess Roman’s ability to detect gaps out to 10 Mpc through visual inspection
and with the gap-finding tool FindTheGap. We conclude that gaps of ≈ 1.5 kpc in streams that are
created from subhalos of masses ≥ 5×106 M⊙ are detectable within a 2–3 Mpc volume in exposures of
1000s–1 hour. This volume contains ≈ 150 galaxies, including ≈ 8 galaxies with luminosities > 109 L⊙.
Large samples of stream gaps in external galaxies will open up a new era of statistical analyses of gap
characteristics in stellar streams and help constrain dark matter models.
Stellar-mass black holes in the Hyades star cluster?Sérgio Sacani
Astrophysical models of binary-black hole mergers in the Universe require a significant fraction of stellar-mass black holes (BHs)
to receive negligible natal kicks to explain the gravitational wave detections. This implies that BHs should be retained even in
open clusters with low escape velocities (≲ 1 km/s). We search for signatures of the presence of BHs in the nearest open cluster
to the Sun – the Hyades – by comparing density profiles of direct 𝑁-body models to data from Gaia. The observations are best
reproduced by models with 2−3 BHs at present. Models that never possessed BHs have an half-mass radius ∼ 30% smaller than
the observed value, while those where the last BHs were ejected recently (≲ 150 Myr ago) can still reproduce the density profile.
In 50% of the models hosting BHs, we find BHs with stellar companion(s). Their period distribution peaks at ∼ 103 yr, making
them unlikely to be found through velocity variations. We look for potential BH companions through large Gaia astrometric and
spectroscopic errors, identifying 56 binary candidates - none of which consistent with a massive compact companion. Models
with 2 − 3 BHs have an elevated central velocity dispersion, but observations can not yet discriminate. We conclude that the
present-day structure of the Hyades requires a significant fraction of BHs to receive natal kicks smaller than the escape velocity
of ∼ 3 km s−1
at the time of BH formation and that the nearest BHs to the Sun are in, or near, Hyades.
A giant thin stellar stream in the Coma Galaxy ClusterSérgio Sacani
The study of dynamically cold stellar streams reveals information about the gravitational potential where they reside and provides
important constraints on the properties of dark matter. However, the intrinsic faintness of these streams makes their detection beyond
Local environments highly challenging. Here, we report the detection of an extremely faint stellar stream (µg,max = 29.5 mag arcsec−2
)
with an extraordinarily coherent and thin morphology in the Coma Galaxy Cluster. This Giant Coma Stream spans ∼510 kpc in length
and appears as a free-floating structure located at a projected distance of 0.8 Mpc from the center of Coma. We do not identify any
potential galaxy remnant or core, and the stream structure appears featureless in our data. We interpret the Giant Coma Stream as
being a recently accreted, tidally disrupting passive dwarf. Using the Illustris-TNG50 simulation, we identify a case with similar
characteristics, showing that, although rare, these types of streams are predicted to exist in Λ-CDM. Our work unveils the presence
of free-floating, extremely faint and thin stellar streams in galaxy clusters, widening the environmental context in which these objects
are found ahead of their promising future application in the study of the properties of dark matter.
The fornax deep_survey_with_vst_i_the_extended_and_diffuse_stellar_halo_of_ng...Sérgio Sacani
We have started a new deep, multi-imaging survey of the Fornax cluster, dubbed Fornax Deep
Survey (FDS), at the VLT Survey Telescope. In this paper we present the deep photometry inside
two square degrees around the bright galaxy NGC 1399 in the core of the cluster. We found that
the core of the Fornax cluster is characterised by a very extended and diffuse envelope surrounding
the luminous galaxy NGC 1399: we map the surface brightness out to 33 arcmin (∼ 192 kpc)
from the galaxy center and down to μg ∼ 31 mag arcsec−2 in the g band. The deep photometry
allows us to detect a faint stellar bridge in the intracluster region on the west side of NGC 1399
and towards NGC 1387. By analyzing the integrated colors of this feature, we argue that it
could be due to the ongoing interaction between the two galaxies, where the outer envelope of
NGC 1387 on its east side is stripped away. By fitting the light profile, we found that exists a
physical break radius in the total light distribution at R = 10 arcmin (∼ 58 kpc) that sets the
transition region between the bright central galaxy and the outer exponential halo, and that the
stellar halo contributes for 60% of the total light of the galaxy (Sec. 3.5). We discuss the main
implications of this work on the build-up of the stellar halo at the center of the Fornax cluster.
By comparing with the numerical simulations of the stellar halo formation for the most massive
BCGs (i.e. 13 < logM200/M⊙ < 14), we find that the observed stellar halo mass fraction is
consistent with a halo formed through the multiple accretion of progenitors with stellar mass in
the range 108 − 1011 M⊙. This might suggest that the halo of NGC 1399 has also gone through
a major merging event. The absence of a significant number of luminous stellar streams and
tidal tails out to 192 kpc suggests that the epoch of this strong interaction goes back to an early
formation epoch. Therefore, differently from the Virgo cluster, the extended stellar halo around
NGC 1399 is characterised by a more diffuse and well-mixed component, including the ICL.
The vvv survey_reveals_classical_cepheids_tracing_a_young_and_thin_stellar_di...Sérgio Sacani
Com o auxílio do telescópio VISTA instalado no Observatório do Paranal do ESO, astrônomos descobriram uma componente anteriormente desconhecida da Via Láctea. Ao mapear a localização de uma classe de estrelas que variam em brilho chamadas Cefeidas, foi descoberto um disco de estrelas jovens enterradas por trás de espessas nuvens de poeira no bojo central.
O rastreio público do ESO VISTA Variables in the Vía Láctea (VVV) [1] usa o telescópio VISTA instalado no Observatório do Paranal para obter imagens múltiplas em épocas diferentes das regiões centrais da nossa Galáxia nos comprimentos de onda do infravermelho [2]. O rastreio está descobrindo uma enorme quantidade de novos objetos, incluindo estrelas variáveis, aglomerados e estrelas em explosão (eso1101, eso1128, eso1141).
Uma equipe de astrônomos, liderada por Istvan Dékány da Pontificia Universidad Católica de Chile, utilizou dados deste rastreio, obtidos entre 2010 e 2014, para fazer uma descoberta notável — um componente anteriormente desconhecido da Via Láctea, a Galáxia que nos acolhe.
JWST early Universe observations and 𝚲CDM cosmologySérgio Sacani
Deep space observations of the James Webb Space Telescope (JWST) have revealed that the structure and
masses of very early Universe galaxies at high redshifts (𝑧~15), existing at ~0.3 Gyr after the BigBang,
may be as evolved as the galaxies in existence for ~10 Gyr. The JWST findings are thus in strong tension
with the ΛCDM cosmological model. While tired light (TL) models have been shown to comply with the
JWST angular galaxy size data, they cannot satisfactorily explain isotropy of the cosmic microwave
background (CMB) observations or fit the supernovae distance modulus vs. redshift data well. We have
developed hybrid models that include the tired light concept in the expanding universe. The hybrid ΛCDM
model fits the supernovae type 1a data well but not the JWST observations. We present a model with
covarying coupling constants (CCC), starting from the modified FLRW metric and resulting Einstein and
Friedmann equations, and a CCC+TL hybrid model. They fit the Pantheon+ data admirably, and the
CCC+TL model is compliant with the JWST observations. It stretches the age of the universe to 26.7 Gyr
with 5.8 Gyr at 𝑧 = 10 and 3.5 Gyr at 𝑧 = 20, giving enough time to form massive galaxies. It thus
resolves the 'impossible early galaxy' problem without requiring the existence of primordial black hole
seeds or modified power spectrum, rapid formation of massive population III stars, and super Eddington
accretion rates. One could infer the CCC model as an extension of the ΛCDM model with a dynamic
cosmological constant.
Detection of anisotropic satellite quenching in galaxy clusters up to z ∼ 1Sérgio Sacani
Satellite galaxies in the cluster environment are more likely to be quenched than galaxies in the general field. Recently, it has
been reported that satellite galaxy quenching depends on the orientation relative to their central galaxies: satellites along the
major axis of centrals are more likely to be quenched than those along the minor axis. In this paper, we report a detection
of such anisotropic quenching up to z ∼ 1 based on a large optically selected cluster catalogue constructed from the Hyper
Suprime-Cam Subaru Strategic Program. We calculate the quiescent satellite galaxy fraction as a function of orientation angle
measured from the major axis of central galaxies and find that the quiescent fractions at 0.25 < z < 1 are reasonably fitted
by sinusoidal functions with amplitudes of a few per cent. Anisotropy is clearer in inner regions (<r200m) of clusters and not
significant in cluster outskirts (>r200m). We also confirm that the observed anisotropy cannot be explained by differences in
local galaxy density or stellar mass distribution along the two axes. Quiescent fraction excesses between the two axes suggest
that the quenching efficiency contributing to the anisotropy is almost independent of stellar mass, at least down to our stellar
mass limit of M∗ = 1 × 1010 M. Finally, we argue that the physical origins of the observed anisotropy should have shorter
quenching time-scales than ∼ 1 Gyr, like ram-pressure stripping, because, for anisotropic quenching to be observed, satellites
must be quenched before their initial orientation angles are significantly changed.
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 physical conditions_in_a_pre_super_star_cluster_molecular_cloud_in_the_an...Sérgio Sacani
Artigo descreve estudo feitos pelos astrônomos utilizando o ALMA para descobrir um proto-aglomerado globular de estrelas gigantes se formando no interior das galáxias Antenas, o famoso par de galáxias em interação. É a primeira vez que os astrônomos conseguem observar um objeto desse tipo nos seus estágios iniciais de vida e com o ambiente ao redor inalterado.
The gaia eso_survey_stellar_content_and_elemental_abundances_in_the_massive_c...Sérgio Sacani
Estudo sobre o conteúdo estelar e os elementos que estão presentes no aglomerado estelar aberto NGC 6705, também conhecido como Aglomerado do Pato Selvagem.
Os astrônomos descobriram um processo único sobre como as maiores galáxias elípticas do universo continuam gerando estrelas muito tempo depois do anos de pico de nascimentos estelares. A alta resolução e a sensibilidade à radiação ultravioleta do Hubble, permitiu aos astrônomos observarem nós brilhantes de estrelas azuis, quentes, se formando juntamente com jatos de buracos negros ativos encontrados nos centros das gigantescas galáxias elípticas.
Combinando dados do Huubble com observações feitas por um conjunto de telescópios baseados tanto em Terra como no espaço, duas equipes independentes descobriram que os jatos dos buracos negros, e as estrelas recém-nascidas são todos partes de um ciclo auto-regulado. Jatos de alta energia atirados do buraco negro aquecem um halo de gás circulante, controlando a taxa com a qual o gás esfria e cai na galáxia.
“Pense no gás ao redor da galáxia como uma atmosfera”, explicou o líder do primeiro estudo, Megan Donahue, da Universidade Estadual do Michigan. “Essa atmosfera pode conter material em diferentes estados, do mesmo modo que a nossa atmosfera tem gás, nuvens e chuva. O que nós estamos vendo é um processo parecido com uma tempestade. À medida que os jatos impulsionam o gás para fora do centro da galáxia, parte do gás esfria e precipita em aglomerados frios que caem de volta para o centro da galáxia como gotas de chuvas”.
“As gotas de chuva eventualmente esfriam o suficiente para tornar-se nuvens de formação de estrelas de gás frio molecular, e a capacidade de observar no ultravioleta distante do Hubble, nos permitiu observar diretamente esses chuviscos de formação de estrelas”, explicou o líder do segundo estudo, Grant Tremblay, da Universidade de Yale. “Nós sabemos que esses chuviscos estão linkados com os jatos, pois eles foram encontrados em filamentos que se dobram ao redor dos jatos, ou abraçam as bordas de bolhas gigantes que os jatos inflaram”, disse Tremblay. “E eles terminam fazendo um redemoinho de gás de formação de estrelas ao redor do buraco negro central”.
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 Exploring the nature and synchronicity of early cluster formation in the Large Magellanic Cloud – II. Relative ages and distances for six ancient globular clusters (20)
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.
The solar dynamo begins near the surfaceSérgio Sacani
The magnetic dynamo cycle of the Sun features a distinct pattern: a propagating
region of sunspot emergence appears around 30° latitude and vanishes near the
equator every 11 years (ref. 1). Moreover, longitudinal flows called torsional oscillations
closely shadow sunspot migration, undoubtedly sharing a common cause2. Contrary
to theories suggesting deep origins of these phenomena, helioseismology pinpoints
low-latitude torsional oscillations to the outer 5–10% of the Sun, the near-surface
shear layer3,4. Within this zone, inwardly increasing differential rotation coupled with
a poloidal magnetic field strongly implicates the magneto-rotational instability5,6,
prominent in accretion-disk theory and observed in laboratory experiments7.
Together, these two facts prompt the general question: whether the solar dynamo is
possibly a near-surface instability. Here we report strong affirmative evidence in stark
contrast to traditional models8 focusing on the deeper tachocline. Simple analytic
estimates show that the near-surface magneto-rotational instability better explains
the spatiotemporal scales of the torsional oscillations and inferred subsurface
magnetic field amplitudes9. State-of-the-art numerical simulations corroborate these
estimates and reproduce hemispherical magnetic current helicity laws10. The dynamo
resulting from a well-understood near-surface phenomenon improves prospects
for accurate predictions of full magnetic cycles and space weather, affecting the
electromagnetic infrastructure of Earth.
Extensive Pollution of Uranus and Neptune’s Atmospheres by Upsweep of Icy Mat...Sérgio Sacani
In the Nice model of solar system formation, Uranus and Neptune undergo an orbital upheaval,
sweeping through a planetesimal disk. The region of the disk from which material is accreted by
the ice giants during this phase of their evolution has not previously been identified. We perform
direct N-body orbital simulations of the four giant planets to determine the amount and origin of solid
accretion during this orbital upheaval. We find that the ice giants undergo an extreme bombardment
event, with collision rates as much as ∼3 per hour assuming km-sized planetesimals, increasing the
total planet mass by up to ∼0.35%. In all cases, the initially outermost ice giant experiences the
largest total enhancement. We determine that for some plausible planetesimal properties, the resulting
atmospheric enrichment could potentially produce sufficient latent heat to alter the planetary cooling
timescale according to existing models. Our findings suggest that substantial accretion during this
phase of planetary evolution may have been sufficient to impact the atmospheric composition and
thermal evolution of the ice giants, motivating future work on the fate of deposited solid material.
Exomoons & Exorings with the Habitable Worlds Observatory I: On the Detection...Sérgio Sacani
The highest priority recommendation of the Astro2020 Decadal Survey for space-based astronomy
was the construction of an observatory capable of characterizing habitable worlds. In this paper series
we explore the detectability of and interference from exomoons and exorings serendipitously observed
with the proposed Habitable Worlds Observatory (HWO) as it seeks to characterize exoplanets, starting
in this manuscript with Earth-Moon analog mutual events. Unlike transits, which only occur in systems
viewed near edge-on, shadow (i.e., solar eclipse) and lunar eclipse mutual events occur in almost every
star-planet-moon system. The cadence of these events can vary widely from ∼yearly to multiple events
per day, as was the case in our younger Earth-Moon system. Leveraging previous space-based (EPOXI)
lightcurves of a Moon transit and performance predictions from the LUVOIR-B concept, we derive
the detectability of Moon analogs with HWO. We determine that Earth-Moon analogs are detectable
with observation of ∼2-20 mutual events for systems within 10 pc, and larger moons should remain
detectable out to 20 pc. We explore the extent to which exomoon mutual events can mimic planet
features and weather. We find that HWO wavelength coverage in the near-IR, specifically in the 1.4 µm
water band where large moons can outshine their host planet, will aid in differentiating exomoon signals
from exoplanet variability. Finally, we predict that exomoons formed through collision processes akin
to our Moon are more likely to be detected in younger systems, where shorter orbital periods and
favorable geometry enhance the probability and frequency of mutual events.
Emergent ribozyme behaviors in oxychlorine brines indicate a unique niche for...Sérgio Sacani
Mars is a particularly attractive candidate among known astronomical objects
to potentially host life. Results from space exploration missions have provided
insights into Martian geochemistry that indicate oxychlorine species, particularly perchlorate, are ubiquitous features of the Martian geochemical landscape. Perchlorate presents potential obstacles for known forms of life due to
its toxicity. However, it can also provide potential benefits, such as producing
brines by deliquescence, like those thought to exist on present-day Mars. Here
we show perchlorate brines support folding and catalysis of functional RNAs,
while inactivating representative protein enzymes. Additionally, we show
perchlorate and other oxychlorine species enable ribozyme functions,
including homeostasis-like regulatory behavior and ribozyme-catalyzed
chlorination of organic molecules. We suggest nucleic acids are uniquely wellsuited to hypersaline Martian environments. Furthermore, Martian near- or
subsurface oxychlorine brines, and brines found in potential lifeforms, could
provide a unique niche for biomolecular evolution.
Continuum emission from within the plunging region of black hole discsSérgio Sacani
The thermal continuum emission observed from accreting black holes across X-ray bands has the potential to be leveraged as a
powerful probe of the mass and spin of the central black hole. The vast majority of existing ‘continuum fitting’ models neglect
emission sourced at and within the innermost stable circular orbit (ISCO) of the black hole. Numerical simulations, however,
find non-zero emission sourced from these regions. In this work, we extend existing techniques by including the emission
sourced from within the plunging region, utilizing new analytical models that reproduce the properties of numerical accretion
simulations. We show that in general the neglected intra-ISCO emission produces a hot-and-small quasi-blackbody component,
but can also produce a weak power-law tail for more extreme parameter regions. A similar hot-and-small blackbody component
has been added in by hand in an ad hoc manner to previous analyses of X-ray binary spectra. We show that the X-ray spectrum
of MAXI J1820+070 in a soft-state outburst is extremely well described by a full Kerr black hole disc, while conventional
models that neglect intra-ISCO emission are unable to reproduce the data. We believe this represents the first robust detection of
intra-ISCO emission in the literature, and allows additional constraints to be placed on the MAXI J1820 + 070 black hole spin
which must be low a• < 0.5 to allow a detectable intra-ISCO region. Emission from within the ISCO is the dominant emission
component in the MAXI J1820 + 070 spectrum between 6 and 10 keV, highlighting the necessity of including this region. Our
continuum fitting model is made publicly available.
WASP-69b’s Escaping Envelope Is Confined to a Tail Extending at Least 7 RpSérgio Sacani
Studying the escaping atmospheres of highly irradiated exoplanets is critical for understanding the physical
mechanisms that shape the demographics of close-in planets. A number of planetary outflows have been observed
as excess H/He absorption during/after transit. Such an outflow has been observed for WASP-69b by multiple
groups that disagree on the geometry and velocity structure of the outflow. Here, we report the detection of this
planet’s outflow using Keck/NIRSPEC for the first time. We observed the outflow 1.28 hr after egress until the
target set, demonstrating the outflow extends at least 5.8 × 105 km or 7.5 Rp This detection is significantly longer
than previous observations, which report an outflow extending ∼2.2 planet radii just 1 yr prior. The outflow is
blueshifted by −23 km s−1 in the planetary rest frame. We estimate a current mass-loss rate of 1 M⊕ Gyr−1
. Our
observations are most consistent with an outflow that is strongly sculpted by ram pressure from the stellar wind.
However, potential variability in the outflow could be due to time-varying interactions with the stellar wind or
differences in instrumental precision.
X-rays from a Central “Exhaust Vent” of the Galactic Center ChimneySérgio Sacani
Using deep archival observations from the Chandra X-ray Observatory, we present an analysis of
linear X-ray-emitting features located within the southern portion of the Galactic center chimney,
and oriented orthogonal to the Galactic plane, centered at coordinates l = 0.08◦
, b = −1.42◦
. The
surface brightness and hardness ratio patterns are suggestive of a cylindrical morphology which may
have been produced by a plasma outflow channel extending from the Galactic center. Our fits of the
feature’s spectra favor a complex two-component model consisting of thermal and recombining plasma
components, possibly a sign of shock compression or heating of the interstellar medium by outflowing
material. Assuming a recombining plasma scenario, we further estimate the cooling timescale of this
plasma to be on the order of a few hundred to thousands of years, leading us to speculate that a
sequence of accretion events onto the Galactic Black Hole may be a plausible quasi-continuous energy
source to sustain the observed morphology
Comparing Evolved Extractive Text Summary Scores of Bidirectional Encoder Rep...University of Maribor
Slides from:
11th International Conference on Electrical, Electronics and Computer Engineering (IcETRAN), Niš, 3-6 June 2024
Track: Artificial Intelligence
https://www.etran.rs/2024/en/home-english/
Richard's aventures in two entangled wonderlandsRichard Gill
Since the loophole-free Bell experiments of 2020 and the Nobel prizes in physics of 2022, critics of Bell's work have retreated to the fortress of super-determinism. Now, super-determinism is a derogatory word - it just means "determinism". Palmer, Hance and Hossenfelder argue that quantum mechanics and determinism are not incompatible, using a sophisticated mathematical construction based on a subtle thinning of allowed states and measurements in quantum mechanics, such that what is left appears to make Bell's argument fail, without altering the empirical predictions of quantum mechanics. I think however that it is a smoke screen, and the slogan "lost in math" comes to my mind. I will discuss some other recent disproofs of Bell's theorem using the language of causality based on causal graphs. Causal thinking is also central to law and justice. I will mention surprising connections to my work on serial killer nurse cases, in particular the Dutch case of Lucia de Berk and the current UK case of Lucy Letby.
Phenomics assisted breeding in crop improvementIshaGoswami9
As the population is increasing and will reach about 9 billion upto 2050. Also due to climate change, it is difficult to meet the food requirement of such a large population. Facing the challenges presented by resource shortages, climate
change, and increasing global population, crop yield and quality need to be improved in a sustainable way over the coming decades. Genetic improvement by breeding is the best way to increase crop productivity. With the rapid progression of functional
genomics, an increasing number of crop genomes have been sequenced and dozens of genes influencing key agronomic traits have been identified. However, current genome sequence information has not been adequately exploited for understanding
the complex characteristics of multiple gene, owing to a lack of crop phenotypic data. Efficient, automatic, and accurate technologies and platforms that can capture phenotypic data that can
be linked to genomics information for crop improvement at all growth stages have become as important as genotyping. Thus,
high-throughput phenotyping has become the major bottleneck restricting crop breeding. Plant phenomics has been defined as the high-throughput, accurate acquisition and analysis of multi-dimensional phenotypes
during crop growing stages at the organism level, including the cell, tissue, organ, individual plant, plot, and field levels. With the rapid development of novel sensors, imaging technology,
and analysis methods, numerous infrastructure platforms have been developed for phenotyping.
What is greenhouse gasses and how many gasses are there to affect the Earth.moosaasad1975
What are greenhouse gasses how they affect the earth and its environment what is the future of the environment and earth how the weather and the climate effects.
Toxic effects of heavy metals : Lead and Arsenicsanjana502982
Heavy metals are naturally occuring metallic chemical elements that have relatively high density, and are toxic at even low concentrations. All toxic metals are termed as heavy metals irrespective of their atomic mass and density, eg. arsenic, lead, mercury, cadmium, thallium, chromium, etc.
DERIVATION OF MODIFIED BERNOULLI EQUATION WITH VISCOUS EFFECTS AND TERMINAL V...Wasswaderrick3
In this book, we use conservation of energy techniques on a fluid element to derive the Modified Bernoulli equation of flow with viscous or friction effects. We derive the general equation of flow/ velocity and then from this we derive the Pouiselle flow equation, the transition flow equation and the turbulent flow equation. In the situations where there are no viscous effects , the equation reduces to the Bernoulli equation. From experimental results, we are able to include other terms in the Bernoulli equation. We also look at cases where pressure gradients exist. We use the Modified Bernoulli equation to derive equations of flow rate for pipes of different cross sectional areas connected together. We also extend our techniques of energy conservation to a sphere falling in a viscous medium under the effect of gravity. We demonstrate Stokes equation of terminal velocity and turbulent flow equation. We look at a way of calculating the time taken for a body to fall in a viscous medium. We also look at the general equation of terminal velocity.
The ability to recreate computational results with minimal effort and actionable metrics provides a solid foundation for scientific research and software development. When people can replicate an analysis at the touch of a button using open-source software, open data, and methods to assess and compare proposals, it significantly eases verification of results, engagement with a diverse range of contributors, and progress. However, we have yet to fully achieve this; there are still many sociotechnical frictions.
Inspired by David Donoho's vision, this talk aims to revisit the three crucial pillars of frictionless reproducibility (data sharing, code sharing, and competitive challenges) with the perspective of deep software variability.
Our observation is that multiple layers — hardware, operating systems, third-party libraries, software versions, input data, compile-time options, and parameters — are subject to variability that exacerbates frictions but is also essential for achieving robust, generalizable results and fostering innovation. I will first review the literature, providing evidence of how the complex variability interactions across these layers affect qualitative and quantitative software properties, thereby complicating the reproduction and replication of scientific studies in various fields.
I will then present some software engineering and AI techniques that can support the strategic exploration of variability spaces. These include the use of abstractions and models (e.g., feature models), sampling strategies (e.g., uniform, random), cost-effective measurements (e.g., incremental build of software configurations), and dimensionality reduction methods (e.g., transfer learning, feature selection, software debloating).
I will finally argue that deep variability is both the problem and solution of frictionless reproducibility, calling the software science community to develop new methods and tools to manage variability and foster reproducibility in software systems.
Exposé invité Journées Nationales du GDR GPL 2024
Professional air quality monitoring systems provide immediate, on-site data for analysis, compliance, and decision-making.
Monitor common gases, weather parameters, particulates.
Salas, V. (2024) "John of St. Thomas (Poinsot) on the Science of Sacred Theol...Studia Poinsotiana
I Introduction
II Subalternation and Theology
III Theology and Dogmatic Declarations
IV The Mixed Principles of Theology
V Virtual Revelation: The Unity of Theology
VI Theology as a Natural Science
VII Theology’s Certitude
VIII Conclusion
Notes
Bibliography
All the contents are fully attributable to the author, Doctor Victor Salas. Should you wish to get this text republished, get in touch with the author or the editorial committee of the Studia Poinsotiana. Insofar as possible, we will be happy to broker your contact.
Exploring the nature and synchronicity of early cluster formation in the Large Magellanic Cloud – II. Relative ages and distances for six ancient globular clusters
1. MNRAS 471, 3347–3358 (2017) doi:10.1093/mnras/stx1702
Advance Access publication 2017 July 6
Exploring the nature and synchronicity of early cluster formation in the
Large Magellanic Cloud – II. Relative ages and distances for six ancient
globular clusters
R. Wagner-Kaiser,1‹
Dougal Mackey,2
Ata Sarajedini,1,3
Brian Chaboyer,4
Roger E. Cohen,5
Soung-Chul Yang,6
Jeffrey D. Cummings,7
Doug Geisler8
and Aaron J. Grocholski9
1Department of Astronomy, University of Florida, 211 Bryant Space Science Center, Gainesville, FL 32611, USA
2Research School of Astronomy & Astrophysics, Australian National University, Canberra, ACT 2611, Australia
3Department of Physics, Florida Atlantic University, 777 Glades Rd, Boca Raton, FL 33431, USA
4Department of Physics and Astronomy, Dartmouth College, Hanover, NH 03755, USA
5Space Telescope Science Institute, Baltimore, MD 21218, USA
6Korea Astronomy and Space Science Institute (KASI), Daejeon 305-348, Korea
7Center for Astrophysical Sciences, Johns Hopkins University, Baltimore, MD 21218, USA
8Departamento de Astronomia, Universidad de Concepcion, Casilla 160-C, Concepcion, Chile
9Department of Physics and Astronomy, Swarthmore College, Swarthmore, PA 19081, USA
Accepted 2017 July 3. Received 2017 June 19; in original form 2017 May 5
ABSTRACT
We analyse Hubble Space Telescope observations of six globular clusters in the Large Magel-
lanic Cloud (LMC) from programme GO-14164 in Cycle 23. These are the deepest available
observations of the LMC globular cluster population; their uniformity facilitates a precise
comparison with globular clusters in the Milky Way. Measuring the magnitude of the main-
sequence turn-off point relative to template Galactic globular clusters allows the relative ages
of the clusters to be determined with a mean precision of 8.4 per cent, and down to 6 per cent
for individual objects. We find that the mean age of our LMC cluster ensemble is identical to
the mean age of the oldest metal-poor clusters in the Milky Way halo to 0.2 ± 0.4 Gyr. This
provides the most sensitive test to date of the synchronicity of the earliest epoch of globular
cluster formation in two independent galaxies. Horizontal branch magnitudes and subdwarf
fitting to the main sequence allow us to determine distance estimates for each cluster and
examine their geometric distribution in the LMC. Using two different methods, we find an
average distance to the LMC of 18.52 ± 0.05.
Key words: globular clusters: individual: NGC 1466 – globular clusters: individual: NGC
1841 – globular clusters: individual: NGC 2210 – globular clusters: individual: NGC 2257 –
globular clusters: individual: Reticulum – globular clusters: individual: Hodge 11.
1 INTRODUCTION
Globular clusters (GCs) have long been a crucial tool to under-
stand star formation processes in the early Universe as well as
the build-up of galactic halo populations. In recent years, high-
precision photometry from the Hubble Space Telescope (HST) has
facilitated accurate and consistent analyses of such clusters. In par-
ticular, the ACS Galactic Globular Cluster Treasury Program has
provided a deep and uniform photometric data base for a large sam-
E-mail: rawagnerkaiser@astro.ufl.edu
ple of Galactic GCs (http://www.astro.ufl.edu/∼ata/public hstgc/
databases.html). Its enduring contribution to the literature includes
a wide range of studies of GC properties, such as mass functions,
binary fractions and horizontal branch (HB) morphology, among
others (Sarajedini et al. 2007; Marı́n-Franch et al. 2009; Dotter
et al. 2010; Paust et al. 2010; Milone et al. 2012; Wagner-Kaiser
et al. 2017).
However, to fully untangle the nature and role of GCs in the
formation and evolution of galaxies, it is necessary to look beyond
the thoroughly studied Galactic globular cluster (GGC) system.
The population of old GCs in the Large Magellanic Cloud (LMC)
provides the next logical step in expanding the sample of targets
for which extremely high-quality photometry can be obtained. We
have recently obtained very deep, uniform HST observations of six
C
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ancient LMC clusters – NGC 1466, NGC 1841, NGC 2210, NGC
2257, Hodge 11 and Reticulum – resulting in photometry extending
well down their main sequences for the first time (Mackey et al.,
in preparation). We can now begin to explore with unprecedented
precision how the timing of the earliest epoch of star cluster for-
mation in the LMC compares to that in the Milky Way, and search
for evidence of an age spread and/or a well-defined age–metallicity
relationship (AMR) in the ancient LMC cluster system.
These goals are of particular significance because recent proper
motion measurements have demonstrated that the Magellanic sys-
tem is likely on its first passage about the Milky Way (e.g.
Kallivayalil, van der Marel Alcock 2006; Besla et al. 2007;
Kallivayalil et al. 2013). The implication is that at the time of GC
formation, the two galaxies were widely separated. Moreover, the
large difference in halo mass and observed star formation histories
between the LMC and the Milky Way suggests that their internal
environments are likely to be substantially different from each other.
Thus, examining the relative ages of the oldest GCs in the LMC and
the Milky Way allows us to begin to quantitatively probe how the
earliest epochs of star formation might vary as a function of location
and environment.
The past several decades have seen a strong push to better under-
stand the chronology of GC formation in the LMC. Brocato et al.
(1996) studied NGC 1786, NGC 1841 and NGC 2210 and deter-
mined ages to ∼20 per cent precision, concluding that metal-poor
clusters in the LMC were coeval with those in the Milky Way to
within ∼3 Gyr. Six additional LMC clusters were studied by Olsen
et al. (1998), who observed a similar consistency with GGC halo
clusters in terms of age, metallicity and HB morphology. Further
work by Johnson et al. (1999) and Mackey Gilmore (2004b) and
Mackey, Payne Gilmore (2006) demonstrated that metal-poor
clusters in the LMC and Milky Way are coeval within ∼1.5–2 Gyr.
In comparison, Harris et al. (1997) showed that the earliest GCs
in the Galactic halo, out to a radius of some 100 kpc (well be-
yond the current distance of the LMC) were all formed within
1 Gyr.
In this paper, we determine the ages of the six clusters in our
LMC sample relative to metal-poor GCs in the Milky Way with
substantially greater precision than any previous work. While abso-
lute ages in principle allow us to place strong constraints on the age
of the Universe, in practice such measurements are significantly less
precise than relative age measurements due to persistent systematic
uncertainties (e.g. metallicity measurements, particular aspects of
stellar evolution, foreground reddening, etc.) such that relative ages
are preferred for this type of analysis. One key advantage that we
exploit here is the availability of data from the Galactic Globular
Cluster Treasury Program, obtained using the same telescope, cam-
era and filters as our LMC observations, and to a comparable depth.
By following closely the methodology developed by Marı́n-Franch
et al. (2009), who explored the relative ages of clusters in the Trea-
sury sample, we measure relative ages for our LMC clusters on the
same scale and as free from biases and systematics as possible.
In addition to the above, we also use our new data to obtain a
precise cluster-based distance estimate to the LMC. Because our
photometry extends several magnitudes down the main sequence
for each target, we are able to employ the method of subdwarf
fitting utilizing the high-quality parallax measurements for several
nearby main-sequence stars determined by Chaboyer et al. (2017)
(GO-11704 and GO-12320). We compare our distance measure-
ments to those derived from the luminosity of the HB – a region
of the colour–magnitude diagram (CMD) observed with very high
signal to noise (≈1500) in our programme.
Many studies over the past decade have demonstrated that GCs
are, in general, not comprised of single stellar populations as once
supposed. Instead, any given cluster appears to possess multiple
stellar generations with a variety of different properties (e.g. Bedin
et al. 2004; Milone et al. 2009; Gratton, Carretta Bragaglia 2012;
Milone et al. 2012; Piotto et al. 2015 for the Galactic clusters,
Dalessandro et al. 2016; Niederhofer et al. 2017a,b for the Small
Magellanic Cloud – SMC – cluster NGC 121). Future work that in-
corporates observations from our HST programme using Wide Field
Camera 3 (WFC3) and the F336W filter will examine the multiple
population properties of our six target LMC clusters. However,
the existence of multiple populations does not significantly affect
cluster CMDs constructed using broad-band optical filters such as
F606W and F814W (except in extreme cases, such as ω Centauri;
Bedin et al. 2004), as the main effects of multiple populations are
concentrated in the blue-UV part of the spectrum (e.g. Sbordone
et al. 2011). Thus, approximating both our LMC targets and the ref-
erence Galactic GCs as single populations for the present analysis
is a valid approach.
This paper is arranged as follows. In Section 2, we discuss the
data set and the relevant photometry. We analyse the clusters to
derive their relative ages in Section 3 and determine distances via
subdwarf and HB fitting in Section 4. Section 5 lists our conclusions.
2 DATA
The data for our analysis come from HST Cycle 23 programme
GO-14164 (PI: Sarajedini). Deep imaging was obtained for six
ancient LMC GCs – NGC 1466, NGC 1841, NGC 2210, NGC
2257, Hodge 11 and Reticulum – through the F606W and F814W
filters with the Advanced Camera for Surveys (ACS) Wide Field
Channel (WFC), and through the F336W filter with the WFC3
Ultraviolet and Visual channel. In this paper, we will consider only
the F606W and F814W data. These six clusters were chosen as they
comprise the complete sample of LMC GCs outside the confusion-
limited crowded stellar fields of the LMC bar region, as well as
spanning a range of galactocentric radius, luminosity and structure.
The locations of the clusters relative to the LMC are shown in
Fig. 1.
Full details of the data acquisition and photometric analysis can
be found in Mackey et al. ( in preparation); here, we provide a
brief description for completeness. Each cluster was observed for
two orbits in the F606W filter resulting in either 13 or 14 images
(depending on the visibility of the target), and for three orbits in the
F814W filter resulting in either 19 or 20 images. Of these image
sets, two each per filter per cluster were short exposures (≈50–70 s
per frame) while the remainder were much longer (∼350–520 s per
frame). We used the DOLPHOT software package (e.g. Dolphin 2000)
to photometer the images, performing one run on the long expo-
sures and one on the short exposures, and then merging the two
quality-filtered output catalogues. To ensure that our photometry
was minimally affected by imperfect charge transfer efficiency)
in the ACS/WFC chips, we utilized the images from the CALACS
pipeline corrected using the pixel-based algorithm of Anderson
Bedin (2010). Our final measurements are on the calibrated VEGA-
mag scale of Sirianni et al. (2005). For each cluster, the photometry
reaches from the top of the red giant branch (RGB) to more than four
magnitudes below the main-sequence turn-off point (MSTOP). The
signal-to-noise ratio around the HB level is ∼1900, the MSTOP is
typically ∼300 per star, and remains at at least ∼30 four magnitudes
fainter than the MSTOP.
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3. Relative ages and distances for LMC GCs 3349
Figure 1. The LMC and the surrounding region. The six clusters from HST
Cycle 23 programme GO-14164 (PI: Sarajedini) are indicated on the image.
For the LMC clusters analysed herein, we adopt metallicities as
summarized in Table 1. The metallicity measurements are largely
from high-resolution spectroscopic observations of these clusters,
with the exception of NGC 1466. NGC 1466 has a photometric
metallicity derived from RR Lyrae observations, and at present
lacks spectroscopic measurements except for a handful of individual
stars. Column 2 notes the metallicities from the cited references
in column 3, which are provided in the metallicity scale noted in
column 4. In order to adopt a consistent metallicity scale throughout
this work, these [Fe/H] measurements are converted to the CG97
(Carretta Gratton 1997) metallicity scale, with the result provided
in the final column of Table 1; use of the CG97 metallicity scale
provides consistency with the Marı́n-Franch et al. (2009) study. The
errors in the transformed metallicities include an assumed 0.2 dex
measurement uncertainty as well as the propagated uncertainties
of the transformation equations (Carretta Gratton 1997; Carretta
et al. 2009).
3 RELATIVE AGES
To determine relative ages for the LMC clusters, we follow closely
the procedure developed by Marı́n-Franch et al. (2009) for their
study of GGC relative ages. By measuring differences in the MSTOP
apparent magnitude with respect to reference clusters, anchoring
the apparent magnitudes to a distance scale and comparing to ex-
pectations from theory, we determine precise relative ages for the
LMC clusters. The details of our methodology are outlined below.
Throughout this process, we adopt the CG97 metallicity scale as
discussed in Section 2; the CG97 scale is also used in Marı́n-Franch
et al. (2009).
A mean ridge line (MRL) is derived to represent the fiducial line
for each cluster. As in Marı́n-Franch et al. (2009), we determine
MRLs for the F606W − F814W, F814W CMD because the subgiant
branch is more vertical and the results are improved with respect to
using F606W as the magnitude. However, in the rest of the analysis,
the F606W−F814W, F606W CMD is used to derive the MSTOP
in F606W magnitude (Marı́n-Franch et al. 2009). To determine the
MRL, we use a moving bin in magnitude with a size of 0.5 mag
and steps of 0.02 mag. The MRL location is determined from the
average of each bin, rejecting 3σ outliers to determine an MRL. We
repeat this MRL-derivation process, shifting the bin locations each
time, to lessen dependence of the result on the bin centres. Over
five iterations, the derived MRLs are combined; a smoothed radial
basis function is used to represent the final fiducial line.
The magnitude of the MSTOP is found by taking the bluest point
of a spline fit locally to the MRL in the MSTOP region. The MSTOP
location is re-determined 10 times, each time offsetting the MRL
bins by 0.01 mag; the adopted MSTOP magnitude for the cluster
is calculated as the mean of these 10 determinations of the bluest
point of the spline. Through this process, we determine apparent
magnitudes in F606W of the MSTOP for the six LMC clusters,
provided in the fourth column of Table 2.
Since this is a relative analysis, the MSTOPs of the LMC clusters
need to be compared to reference MSTOP locations. Two particular
regions along the fiducial lines were designated by Marı́n-Franch
et al. (2009) to be minimally affected by age; specifically, on the
main sequence (MMSTOP, F606W+3 ≤ m ≤ MMSTOP, F606W+1.5) and
on the RGB (MMSTOP, F606W −2.5 ≤ m ≤ MMSTOP, F606W −1.5). Be-
cause these RGB and MS regions are largely unaffected by age, a
comparison of MSTOP magnitude between the reference and MRL
gives an indication of the relative age of two clusters. The MRL of
these two locations are used to ‘shift’ the entire MRL of a reference
cluster in colour and magnitude to match the same regions in each
LMC cluster. In doing so, any differences in line-of-sight reddening
between the clusters are automatically accounted for, making the
age determinations free of assumptions of distance or reddening.
By using the GGC clusters as reference clusters, we thus determine
the differences in MSTOP magnitudes with respect to the LMC
clusters.
We use the same GGC reference clusters as Marin-Franch et al.
(2009) across the following metallicity ranges: NGC 6981 (−1.3 ≤
[Fe/H] −1.1), NGC 6681 (−1.5 ≤ [Fe/H] −1.3), NGC 6101
(−1.8 ≤ [Fe/H] −1.5) and NGC 4590 (−2.3 ≤ [Fe/H] −1.8).
Table 1. Assumed metallicities for our target LMC clusters.
Cluster [Fe/H]ref Reference Original scale [Fe/H]CG97
NGC 1466 −1.9a Walker (1992a) ZW84 −1.70 ± 0.50
NGC 1841 −2.02 Grocholski et al. (2006) CG97 −2.02 ± 0.20
NGC 2210 −1.65 Mucciarelli et al. (2010) C09 −1.45 ± 0.20
NGC 2257 −1.95 Mucciarelli et al. (2010) C09 −1.71 ± 0.20
Hodge11 −2.00 Mateluna et al. (2012) C09 −1.76 ± 0.20
Reticulum −1.57 Grocholski et al. (2006) CG97 −1.57 ± 0.20
Note. aMeasurement only given to one decimal precision by Walker (1992a). The propagation of error from the conversion
of the measurement from the ZW84 scale to the CG97 scale leads to a generous uncertainty in metallicity.
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Table 2. Relative ages for our LMC cluster sample.
Cluster [Fe/H]CG97
a Ref. clusterb mF606W, MSTOP MF606W, MSTOP Relative age (Gyr) Absolute age (Gyr)
NGC 1466 −1.70 NGC 6101 22.62 ± 0.02 3.75 ± 0.18 12.18 +0.95
−1.12 13.38 +1.67
−2.28
NGC 1841 −2.02 NGC 4590 22.61 ± 0.02 3.64 ± 0.17 12.57 +0.47
−1.57 13.77 +1.05
−2.41
NGC 2210 −1.45 NGC 6681 22.34 ± 0.02 3.70 ± 0.18 10.43 +1.15
−1.06 11.63 +1.80
−1.12
NGC 2257 −1.71 NGC 6101 22.32 ± 0.01 3.69 ± 0.18 11.54 +1.08
−1.28 12.74 +1.87
−2.18
Hodge11 −1.76 NGC 6101 22.56 ± 0.01 3.78 ± 0.17 12.72 +0.65
−0.85 13.92 +1.48
−2.01
Reticulum −1.57 NGC 6101 22.31 ± 0.01 3.79 ± 0.17 11.89 +0.87
−0.82 13.09 +2.21
−1.98
Notes. aFrom Table 1.
bAs in Marı́n-Franch et al. (2009).
Figure 2. A comparison of the LMC fiducial sequences (dotted black lines) to the shifted reference Galactic cluster fiducials (solid blue lines, see Table 2). The
intervals upon which the least-squares match is performed are indicated by the thick regions for each fiducial. The location of the LMC MSTOP is indicated
by the open green circle and by the maroon triangle for the Galactic reference cluster MSTOP location.
We use a least squares approach to minimize offsets between the
MRL of the reference clusters and the LMC clusters in the inter-
vals defined by Marı́n-Franch et al. (2009) and described above.
The result of this process is demonstrated in Fig. 2, where each
LMC cluster (black dotted lines) is compared to the relevant GGC
reference (blue solid lines). The fiducials of the GGC reference
clusters are shifted to match the LMC clusters in the regions of the
CMD discussed above; these regions are also highlighted in Fig. 2.
The MSTOP for the LMC (green) and reference Galactic cluster
(maroon) are also indicated in the plot. While the fiducials for the
LMC clusters are largely consistent with their GGC reference clus-
ter counterpart, we note that there is a slight mismatch between the
NGC 1841 and NGC 4590 fiducials on the upper RGB. This does
not appear to be driven by our approach but may be due to differing
metallicities or [α/Fe] abundances between the two clusters.
As in Marı́n-Franch et al. (2009), shifts among the set of GGC
reference clusters are determined by matching MRL for the refer-
ence clusters in adjacent metallicity ranges. The absolute MSTOP
magnitude in F606W for NGC 6752 of 3.87 ± 0.15 for calibration is
adopted, as are comparable uncertainties arising from the method-
ology, to be consistent with Marı́n-Franch et al. (2009). This allows
us to obtain the absolute magnitude of the MSTOP, given in the
fifth column of Table 2. As the uncertainty in the distance of NGC
6752 affects the absolute age scale rather than the relative age scale,
we do not include this in our error budget. In re-deriving cluster
ages from Marı́n-Franch et al. (2009) for clusters with [Fe/H] ≤
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5. Relative ages and distances for LMC GCs 3351
Figure 3. The magnitude of the MSTOP of the LMC clusters (green circles)
according to their assumed metallicities. The MSTOP determined for GGCs
from Marı́n-Franch et al. (2009) are plotted as blue triangles. The solid lines
delineate the MSTOP from the theoretical models (Dotter et al. 2008) from
6 Gyr (upper right) to 15 Gyr (lower left) at 0.5 Gyr intervals, alternating solid
and dashed lines for clarity. The Galactic reference clusters are indicated by
the coloured squares. The theoretical grid assumes [α/Fe] = 0.2.
−1.5, we find a minimal mean offset of the MSTOP magnitudes of
0.01 ± 0.03; this is incorporated into our cited errors.
We plot the MSTOP magnitude estimates for the six LMC clus-
ters alongside the GGC MSTOP magnitudes from Marı́n-Franch
et al. (2009) in Fig. 3. From a grid of Dartmouth Stellar Evolution
Database (DSED; Dotter et al. 2008) isochrones at 0.1 dex metal-
licity intervals, the smoothed, diagonal lines in this figure indicate
MSTOP locations for isochrones ranging in age from 6 Gyr (upper
right) to 15 Gyr (lower left) in steps of 0.5 Gyr. For clarity, we
alternate between solid and dashed lines. Additionally, the LMC
clusters show enhancement in [α/Fe] comparable to the enhance-
ment seen in the GGCs (Mucciarelli, Origlia Ferraro 2010). The
grid in Fig. 3 is generated assuming an α-enhanced model ([α/Fe]
= 0.2). The grid of Dotter et al. (2008) DSED isochrones are used
to derive MSTOP in the same iterative process as described above
– fitting a spline locally to the MSTOP and determining the bluest
point. This facilitates a comparison between the calibrated MSTOP
magnitudes from the observed clusters to the theoretical models to
determine ages. We interpolate between the models to determine
ages for the six LMC clusters, presented in Table 2.
The relative ages we derive are consistent with the LMC clusters
having similar properties to the old, inner halo Milky Way clusters.
However, we note that the metallicities of the LMC clusters are
not fully agreed upon in the literature; if our adopted metallicities
are inaccurate then our conclusions on the relative ages of these
clusters may need re-examination. We estimate a change of 0.1
dex in metallicity leads to a change of up to ≈0.4 Gyr in relative
age. Nevertheless, our relative age determinations are a significant
improvement on more uncertain age estimates from previous studies
of these clusters (Brocato et al. 1996; Olsen et al. 1998; Piatti
et al. 2009; Jeon et al. 2014). Through our analysis, relative ages
are determined with precision between 6 per cent (Hodge 11) and
10 per cent (NGC 2210), with a mean precision across the sample
of 8.4 per cent.
With our substantial improvement in LMC cluster age measure-
ments over previous studies, we can re-examine the coevality of GC
formation in the Milky Way Galaxy (MWG) and the LMC – two
galaxies that are thought to have been widely separated at the epoch
of cluster formation (Kallivayalil et al. 2006, 2013), and which thus
present independent and very different formation environments, as
the MWG is a more massive and metal-rich galaxy than the LMC.
Previous work has indicated that early cluster formation in the Milky
Way and LMC was broadly concurrent within 1.5–2 Gyr (Brocato
et al. 1996; Olsen et al. 1998; Johnson et al. 1999; Mackey
Gilmore 2004a).
We propagate the individual errors of the relative age estimates
from Table 2 and find an average age for the LMC clusters of
11.8 ± 0.4 Gyr (0.8 Gyr stddev). For the Galactic clusters in a simi-
lar metallicity range ([Fe/H] ≤ −1.5), the mean age is 12.0 ± 0.2 Gyr
(0.6 Gyr stddev). Consequently, this suggests the two sets of metal-
poor old clusters are coeval within 0.2 ± 0.4 Gyr (1.0 Gyr stddev).
As the best test of the synchronicity of GC formation in two com-
pletely unrelated galaxies so far, we find clear evidence that the first
epoch of GC formation occurred essentially simultaneously in these
two completely different galactic environments.
The metal-poor Sagittarius clusters have also been found to be
very similar to those in our Galaxy (Mackey Gilmore 2004b;
Marı́n-Franch et al. 2009). Terzan 8 is the one cluster in the Sagit-
tarius dwarf galaxy that is more metal-poor than −1.5 on the CG97
scale. Marı́n-Franch et al. (2009) find the age of this cluster to be
within 0.5 ± 0.5 Gyr of the mean value we quoted above. However,
this trend does not necessarily seem to be consistent in the SMC.
While NGC 121 is the only ‘old cluster in the SMC, the majority of
recent work suggests it is younger than the oldest Galactic clusters
despite having similar metallicity; estimates put the age in the range
of 10.5–11.8 Gyr, depending on study and model choice (Mighell,
Sarajedini French 1998; Dolphin et al. 2001; Glatt et al. 2008).
However, NGC 121 has not been measured on the same relative age
scale we use herein and a direct comparison is incomplete in this
respect. Although the MWG, LMC and Sagittarius appear to have
closely synchronous initial metal-poor GC formation, the example
of the SMC indicates that this may not be universal.
The ages derived here are relative ages, not absolute ages. To
compare ages directly with previous studies, a reference absolute
age must be adopted. From the absolute ages of O’Malley, Gilligan
Chaboyer (2017), we use the mean absolute age of the GGC
reference clusters to calibrate our LMC relative ages to absolute
ages. Specifically, O’Malley et al. (2017) found ages of 12.4 ±
1.3 Gyr for NGC 4590, 13.4 ± 1.5 Gyr for NGC 6101 and 12.5 ±
1.7 Gyr for NGC 6681, and we adopt a mean age of 12.8 ± 00.9 Gyr
(note that this is the same absolute age adopted by Marı́n-Franch
et al. 2009 as well). This absolute age is compared to the mean
relative ages of these same clusters (11.6 Gyr); the LMC clusters’
relative ages are adjusted according to the difference of 1.2 Gyr.
These values are listed in the final column of Table 2 and include
the uncertainty of 0.15 mag in the absolute magnitude of the MSTOP
for NGC 6752, the zero-point cluster.
Using these absolute ages, the AMR is reconstructed in Fig. 4
using ages of the Galactic clusters from VandenBerg et al. (2013,
left), Dotter et al. (2010, middle) and Marı́n-Franch et al. (2009,
right, assuming reference age of 12.8 Gyr). The LMC clusters are
plotted for comparison (green circles). Our results may be compared
directly to Marı́n-Franch et al. (2009). With respect to VandenBerg
et al. (2013) and Dotter et al. (2010), the comparisons are qualitative,
as different methods and age calibrations may lead to vertical offsets
in Fig. 4.
As in Fig. 3, the LMC clusters appear to more closely mimic the
old, metal-poor inner halo Galactic clusters. NGC 2210 could plau-
sibly be younger than the other LMC clusters, although this is not
a statistically significant deviation. None the less, from inspection
of the AMR, it is possible that NGC 2210 may be more similar to
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6. 3352 R. Wagner-Kaiser et al.
Figure 4. The AMR for the GGCs and the LMC clusters, compared. The leftmost panel shows ages from (VandenBerg et al. 2013, red squares), the middle
panel shows ages from (Dotter et al. 2010, cyan diamonds) and the ages from (Marı́n-Franch et al. 2009, blue triangles). Our results may be compared directly
to Marı́n-Franch et al. (2009), and qualitatively with VandenBerg et al. (2013) and Dotter et al. (2010), who employ different methods and age calibrations.
Galactic clusters belonging to the younger branch of the AMR (the
outer halo; presumably accreted clusters) than the older branch (the
inner halo; likely in situ clusters). Although there is no sufficient
evidence here to make a strong conclusion, it is certainly of interest
to pursue in future work in order to better understand the formation
history of the LMC and its GC system.
4 DISTANCES
4.1 Horizontal branch
To obtain distance estimates from observations of the HB, fiducials
of the HBs are created for the LMC clusters and compared to several
reference GGC clusters. We initially estimate the cluster HB fiducial
by eye and fit a cubic spline to the points. To iterate on this and
obtain a better estimate, the HB is binned in intervals of colour of
0.04 along the initial spline, overlapping by 0.01. In each colour
bin, using stars within a 3σ range of the initial spline, we determine
the average magnitude of the HB in that bin. These results are used
to re-determine the HB with a cubic spline, as seen by the solid
blue line in Fig. 5 for each LMC cluster, where the included HB
stars are indicated (cyan points). We note that while blue straggler
stars or field stars may contaminate the included HB stars, their low
frequency is unlikely to skew the estimated HB fiducials.
This process is repeated for six GGC reference clusters to serve as
comparisons to the HB fiducials of the LMC clusters. These Galactic
clusters are chosen to (i) have low reddening, (ii) have a populated
HB and (iii) have available photometry in the same HST filters from
Sarajedini et al. (2007). Using the same method described above, we
derive HB fiducials for two moderately metal-rich Galactic clusters
(NGC 5272 and NGC 6584), two intermediate metallicity clusters
(NGC 5024 and NGC 6809) and two metal-poor clusters (NGC
4590 and NGC 6341), as shown in Fig. 6. We adopt the foreground
reddenings and distance moduli from the Harris (2010) catalogue1
for these reference clusters; these values are listed in Table 3. We
note that Harris (2010) derive their distances from the assumption
that MV(HB) = 0.16 [Fe/H] + 0.84 and their E(B − V) from an
average of several measurements; we assume a reddening law of RV
= 3.1 (Cardelli, Clayton Mathis 1989). Additionally, the Harris
(2010) catalogue metallicities are on the C09 scale; for consistency
1 http://physwww.mcmaster.ca/harris/mwgc.dat
(as in Section 2), we convert these to the CG97 scale, and these
values are listed in Table 3.
In order to obtain distance measurements, we assume reddenings
for the LMC clusters from Walker (1992a,b, 1993), as indicated
in Table 4. While an assumption of reddening is necessary to de-
rive distances, the accuracy of the adopted reddening values could
plausibly affect our distance estimates. However, the reddening esti-
mates we adopt are found to differ on average from the foreground
reddening estimates of Schlegel, Finkbeiner Davis (1998) and
Schlafly Finkbeiner (2011) by ∼0.006.
With the derived HB fiducials, the fiducials from the GGC ref-
erence clusters are shifted to match those of the LMC clusters in a
least-squares fashion, as shown in Fig. 7. The resulting shift in mag-
nitude from this fit, in conjunction with the assumed GGC distances
from Table 3, determines the distance for each LMC cluster. Each
LMC cluster has its distance derived with respect to two reference
GGC cluster fiducials, as indicated in the fourth column of Table 4.
The final column of this table provides the average of those two
distances.
The cited uncertainties on the derived distances in Table 4 incor-
porate the scatter (standard deviation in magnitude) and number of
stars used to derive each LMC fiducial, the scatter and number of
stars for the GGC fiducials, and the errors from the least-squares
fitting between the GGC and LMC fiducials.
Through this process, we obtain an average distance of
18.59 ± 0.06 across the six clusters, in line with previous studies
for the LMC distance of approximately μ = 18.49 ± 0.09 (de Grijs,
Wicker Bono 2014). Further distance determination comparisons
are discussed at the end of Section 4.2.
4.2 Subdwarf analysis
As the most well-understood phase of stellar evolution, fitting of
main-sequence stars offers an opportunity to provide excellent dis-
tance measurements. Using parallaxes and highly precise HST pho-
tometry of local subdwarfs from GO-11704 (Chaboyer et al. 2017),
we leverage the accurately measured subdwarf absolute magnitudes
and the clean main sequences of the six LMC clusters to determine
distances. Details of the four subdwarfs in the metallicity range of
the LMC clusters are presented in Table 5. The magnitudes and
colours of these stars are adjusted for their individual reddening,
noted in Column 5.
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7. Relative ages and distances for LMC GCs 3353
Figure 5. Fiducial HBs for the six LMC clusters in our sample. In each panel, the HST photometry is plotted in black, the included stars are the larger cyan
points and the fiducial spline (see the text for details) is indicated by the solid blue line. The cluster name and number of stars (N*) included in the fit are
indicated in the lower left side of each panel.
In order to compare the observed main sequences of the LMC
clusters to the photometry for the local subdwarfs, it is necessary to
adjust the colours of the latter to account for the various metallicities
of the clusters and the subdwarfs. First, the metallicities of the
individual stars are adjusted for their unique [α/Fe] abundances
using the following relation from Salaris, Chieffi Straniero (1993)
and Dotter et al. (2010):
[M/H] = [Fe/H] + log(0.638 × 10[α/Fe]
+ 0.362). (1)
A grid of DSED isochrones for the HST/ACS filters over a metal-
licity range of −2.5 to −0.5 and an absolute magnitude range of
4.5 MF606W 7 is used. In this grid, we interpolate based on the
metallicity of each star to determine the change in colour necessary
to correct the F606W−F814W colour of the subdwarf to the refer-
ence metallicity of each of the clusters. The reference metallicity of
each LMC cluster is also corrected as in equation (1) for an assumed
α-enhancement of [α/Fe] = 0.2.
Assuming a reddening for each LMC cluster (Walker 1992b,
1993, see Table 6), a main-sequence fiducial is fit with a power law
for cluster stars between an absolute F606W magnitude of 4.5 and 7
in overlapping magnitude bins of 0.1 mag. The fiducials are shown
in the panels of Fig. 8 as red curves for each cluster. The fiducial is
shifted via least squares to minimize the offsets of the HST parallax
stars from the fiducial line in magnitude. The resulting distance
moduli are given in the final column of Table 6, with the quoted
error representing the uncertainty in the fiducial fit.
We find an average distance modulus to the LMC of
18.40 ± 0.04(47.94 ± 0.32 kpc). This is shorter than the mean
distance we determined from the HB analysis in Section 4.1 of
18.59 ± 0.06. The two estimates are within 3σ but discrepant.
This is likely due to different underlying assumptions, as discussed
further at the end of this section. From the HB and subdwarf dis-
tances, we derive an average distance to the LMC of 18.52 ± 0.05
(50.51 ± 1.19 kpc).
Radial velocity measurements suggest that even the oldest clus-
ters in the LMC lie in the disc (Schommer et al. 1992; Grocholski
et al. 2006, 2007). Due to the inclination of the LMC on the sky,
a simple average of cluster distances assumes a random distribu-
tion and could result in a biased distance estimate. However, if we
assume the LMC clusters lie in a disc, geometric variations may
be accounted for. The locations of the clusters on the sky are used
to correct the individual distances for the inclination of the disc,
thereby obtaining a more accurate absolute distance for the LMC.
By doing so, we obtain an estimate of the distance to the centre of
the LMC that is more accurate by accounting for the geometry of
the galaxy.
This process is outlined in van der Marel Cioni (2001) and
Grocholski et al. (2007), and also presented in the equations (2)
through (5) below. The distance to the LMC centre is denoted by
D0. D is the distance to any location on the disc plane; in our case,
this is the distance to each cluster. We assume the LMC disc to be
inclined to the plane of the sky by the angle i around an axis at
the position angle θ. θ is measured anticlockwise from the west; to
align with usual astronomical convention, is defined the position
angle from the north ( = θ – 90). These values are adopted from
van der Marel Cioni (2001); we note that Grocholski et al. (2007)
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8. 3354 R. Wagner-Kaiser et al.
Figure 6. Fiducial HBs for the reference GGCs in our sample. In each panel, the HST photometry is plotted in black, the included stars are the larger cyan
points and the fiducial spline (see the text for details) is indicated by the solid blue line. The cluster name and number of stars (N*) included in the fit are
indicated in the lower left of each panel.
Table 3. GGC HB calibration clusters.
Cluster [Fe/H]CG97 E(B − V) Distance modulus
NGC 5272 −1.32 ± 0.19 0.01 15.07
NGC 6584 −1.32 ± 0.20 0.10 15.96
NGC 5024 −1.84 ± 0.20 0.02 16.32
NGC 6809 −1.70 ± 0.20 0.08 13.89
NGC 4590 −1.96 ± 0.20 0.05 15.21
NGC 6341 −2.03 ± 0.21 0.02 14.65
explored a variety of geometries from other past works, finding
differences in the resulting distance of 0.2 kpc for varying i and
. The right ascension and declination are referred to, respectively,
by α and δ in the equations below,
D/D0 = cos i/[cos i cos ρ − sin i sin ρ sin (φ − θ)]. (2)
To calculate the distance to the LMC centre (D0 above), it is
necessary to calculate ρ and sin (φ − θ). The former is calculated
as in equation (3):
cos ρ = cos δ cos δ0 cos (α − α0) + sin δ sin δ0. (3)
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9. Relative ages and distances for LMC GCs 3355
Figure 7. In each panel, the HST photometry is plotted in black. The shifted HB fiducials of the reference clusters are indicated by the dashed blue and
magenta lines. The solid cyan line indicates the fiducial of the LMC cluster.
Via a typical trigonometric expansion, sin (φ − θ) may be deter-
mined as sin (φ − θ) = sin (φ) cos (θ) – cos (φ) sin (θ). These
components are detailed in equations (4) and (5):
sin ρ cos φ = − cos δ sin (α − α0) (4)
sin ρ sin φ = sin δ cos δ0 − cos δ sin δ0 cos α − α0. (5)
Through these equations, we determine an average, error-
weighted distance modulus to the LMC centre of D0 = 18.20 ± 0.06,
equivalent to 46.42 ± 0.45 kpc. However, NGC 1841 is a clear out-
lier in these data, lying more than 3σ from the mean D0 distance
to the LMC centre, leading to several possibilities. One interpreta-
tion of these results suggests that NGC 1841 may not be a member
of the LMC disc or may have been pulled out of the LMC disc
(Grocholski et al. 2007). Another view is that an uncertain estimate
of the reddening could be affecting the distance measurement; if
the reddening of NGC 1841 is doubled from E(B − V) = 0.18, it is
brought into agreement with the LMC mean distance. Regardless
of the reason(s) for the discrepancy, we remove NGC 1841 as an
anomaly and continue determining the distance to the LMC centre.
Leaving out the extreme outlier of NGC 1841, the error-weighted
mean is 18.41 ± 0.04 (48.29 ± 0.38 kpc). This is within the range
of the result from Section 4.1 from the HB analysis, as seen in
Fig. 9, where the subdwarf distances and the subdwarf distances
adjusted for the LMC geometry are compared to those derived
from the HB analysis. The subdwarf distances tend to be shorter
by 0.14 mag on average than those of the HB analysis; the ad-
justed subdwarf distances are also shorter than the HB distances
by 0.12 (leaving NGC 1841 out). The offset appears to be con-
sistent regardless of the individual cluster. The systematic bias
between the derived distances could be due to the combination
of necessary assumptions in the two approaches (e.g. metallicity,
Table 4. Distance estimates: ZAHB.
Cluster [Fe/H]CG97
a Assumed E(B − V)b E(B − V)c Reference HBs μZAHB
NGC 1466 −1.70 0.09 0.07 NGC 5024, NGC6809 18.67 ± 0.08
NGC 1841 −2.02 0.18 0.19 NGC 4590, NGC6341 18.58 ± 0.05
NGC 2210 −1.45 0.06 0.08 NGC 5272, NGC6584 18.52 ± 0.04
NGC 2257 −1.71 0.04 0.06 NGC 5024, NGC6809 18.61 ± 0.07
Hodge 11 −1.76 0.08 0.08 NGC 5024, NGC6809 18.57 ± 0.08
Reticulum −1.57 0.03 0.02 NGC 5272, NGC6584 18.57 ± 0.06
Notes. aAs in Table 1.
bAbsorptions adopted from Walker (1992, 1993), assuming RV = 3.1.
cAbsorptions from Schlegel et al. (1998) for comparison, assuming RV = 3.1.
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10. 3356 R. Wagner-Kaiser et al.
Table 5. Properties of the reference subdwarfs used for cluster distance measurements.
ID (mas) F606W F814W E(B − V) [Fe/H] [α/Fe]
HIP46120 14.49 ± 0.16 9.938 ± 0.0015 9.371 ± 0.0017 0.00 −2.24 0.29
HIP103269 14.12 ± 0.10 10.084 ± 0.0034 9.503 ± 0.0027 0.00 −1.85 0.06
HIP106924 14.48 ± 0.12 10.156 ± 0.0024 9.555 ± 0.0048 0.00 −2.22 0.23
HIP108200 12.39 ± 0.08 10.785 ± 0.0031 10.143 ± 0.0055 0.02 −1.83 0.01
Table 6. Distance estimates: subdwarf fitting.
Cluster Assumed values
name E(B − V)a [Fe/H]b μ D (kpc) μ0 D0 (kpc)
NGC 1466 0.09 − 1.7 18.66 ± 0.03 53.94 ± 0.80 18.40 ± 0.06 47.90 ± 1.29
NGC 1841 0.18 − 2.02 18.34 ± 0.04 46.61 ± 0.86 17.85 ± 0.11 37.10 ± 1.89
NGC 2210 0.06 − 1.45 18.32 ± 0.04 46.05 ± 0.80 18.34 ± 0.02 46.58 ± 0.38
NGC 2257 0.04 − 1.71 18.25 ± 0.04 44.60 ± 0.82 18.39 ± 0.04 47.59 ± 0.86
Hodge 11 0.08 − 1.76 18.53 ± 0.03 50.83 ± 0.81 18.54 ± 0.02 51.02 ± 0.43
Reticulum 0.03 − 1.57 18.35 ± 0.03 46.84 ± 0.68 18.42 ± 0.04 48.35 ± 0.97
aE(B − V) adopted from Walker (1992b, 1993).
bFrom Table 1.
Figure 8. Subdwarf fitting to the main sequences of the LMC clusters. The photometry is shown in black. A fiducial, in red, is fit to the de-reddened cluster
photometry. The subdwarfs, shown in cyan, are offset in magnitude to minimize the standard deviation to the fiducial, resulting in an estimate of the cluster
distance.
reddening, GGC distances) or the zero-points. The HB distance
calibration relies on the assumed metallicity–magnitude scale from
Harris (2010), which is more likely to result in a systematic off-
set relative to the more fundamentally derived subdwarf distances.
Regardless, the overall distance estimates of the LMC cluster sys-
tem from the two methods are in reasonable (though not excellent)
agreement.
Our estimated distance D0 to the centre of the LMC is also com-
parable to, though marginally shorter than, recent determinations of
the LMC distance of 18.49 ± 0.09 (de Grijs et al. 2014 and refer-
ences therein) and 18.493 mag 0.008 (statistical) 0.047 (systematic;
Pietrzyński et al. 2013). Our result is comparable to the values of
18.40 ± 0.04 and 47.9 ± 0.9 kpc, derived from Grocholski et al.
(2007) via red clump distances from K-band observations for 25
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11. Relative ages and distances for LMC GCs 3357
Figure 9. Distances derived from the HB analysis are compared
to the subdwarf distances (blue triangles) and subdwarf distances adjusted
for the LMC geometry (red squares). The y-axis is calculated by subtracting
the subdwarf derived distances from the HB distance estimates. The outlying
point is NGC 1841. While there is an offset between the two approaches, it
appears to be zero-point related and does not vary with distance.
clusters in the LMC, also taking into account the geometry of the
LMC disc. The two studies agree despite differences from our sam-
ple being smaller and our focus on the old GCs. The true distance
modulus derived from Johnson et al. (1999) of 18.46 ± 0.09 from
three LMC clusters is also comparable to our derived 18.41 ± 0.04
(48.29 ± 0.38 kpc). In all cases, the results are consistent within the
uncertainties.
5 CONCLUSIONS
In this paper, we have used new deep homogeneous photometry for
six ancient GCs in the LMC to measure the epoch of metal-poor
GC formation relative to that in the Milky Way, and calculate a new
distance estimate to the LMC. Our main results are as follows.
(i) By utilizing the same methodology as employed by MF09, we
have calculated reddening and distance-independent relative ages
for our six targets with a mean precision of 8.4 per cent, and down
to 6 per cent for individual clusters. The LMC sample is coeval
with the metal-poor inner halo Galactic GCs measured by MF09 to
within 0.2 ± 0.4 (1.0 Gyr stddev). This is despite the fact that the
LMC was most likely widely separated from the Milky Way at this
time, and despite the significantly different formation environments
implied by the different halo masses of the LMC and Milky Way.
(ii) Through HB magnitude and subdwarf fitting methods, we
have determined two distance estimates to the LMC. These are
18.59 ± 0.06 and 18.40 ± 0.04, respectively. There is a systematic
mean difference between the individual cluster distance determina-
tions of ∼0.14 mag; this could be due to differences in the underly-
ing assumptions for the two different methodologies (for example,
the assumed distances of the reference GGCs in the HB analysis
versus the assumed metallicities of the LMC clusters during the
subdwarf analysis). The average distance from the two methods
is 18.52 ± 0.05 (50.51 ± 1.19 kpc), which is comparable to the
distance modulus derived recently by de Grijs et al. (2014).
(iii) To counter the possibility that our distance estimate could
be biased if the target clusters are members of the LMC disc, we
calculate a geometrically corrected subdwarf distance to the LMC
of 18.41 ± 0.04 (48.29 ± 0.38 kpc), where the measurement for
NGC 1841 has been excluded as an outlier.
ACKNOWLEDGEMENTS
We thank an anonymous referee whose comments and sugges-
tions were very helpful. DM is grateful for support from an Aus-
tralian Research Council Future Fellowship (FT160100206). DG
gratefully acknowledges support from the Chilean BASAL Centro
de Excelencia en Astrofı́sica y Tecnologı́as Afines (CATA) grant
PFB-06/2007.
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