We present the detection of 89 low surface brightness (LSB), and thus low stellar
density galaxy candidates in the Perseus cluster core, of the kind named ‘ultra-diffuse
galaxies’, with mean effective V-band surface brightnesses 24.8–27.1 mag arcsec−2
, total
V-band magnitudes −11.8 to −15.5 mag, and half-light radii 0.7–4.1 kpc. The candidates
have been identified in a deep mosaic covering 0.3 deg2
, based on wide-field
imaging data obtained with the William Herschel Telescope. We find that the LSB
galaxy population is depleted in the cluster centre and only very few LSB candidates
have half-light radii larger than 3 kpc. This appears consistent with an estimate of
their tidal radius, which does not reach beyond the stellar extent even if we assume
a high dark matter content (M/L = 100). In fact, three of our candidates seem to
be associated with tidal streams, which points to their current disruption. Given that
published data on faint LSB candidates in the Coma cluster – with its comparable central
density to Perseus – show the same dearth of large objects in the core region, we
conclude that these cannot survive the strong tides in the centres of massive clusters.
The network of filaments with embedded clusters surrounding voids, which has been seen in maps derived from
redshift surveys and reproduced in simulations, has been referred to as the cosmic web. A complementary
description is provided by considering the shear in the velocity field of galaxies. The eigenvalues of the shear
provide information regarding whether or not a region is collapsing in three dimensions, which is the condition for
a knot, expanding in three dimensions, which is the condition for a void, or in the intermediate condition of a
filament or sheet. The structures that are quantitatively defined by the eigenvalues can be approximated by isocontours
that provide a visual representation of the cosmic velocity (V) web. The current application is based on
radial peculiar velocities from the Cosmicflows-2 collection of distances. The three-dimensional velocity field is
constructed using the Wiener filter methodology in the linear approximation. Eigenvalues of the velocity shear are
calculated at each point on a grid. Here, knots and filaments are visualized across a local domain of
diameter ~0.1c
A giant ring_like_structure_at_078_z_086_displayed_by_gr_bsSérgio Sacani
Uma equipe de astrônomos da Hungria e dos EUA descobriram o que parece ser a maior feição no universo observável: um anel de nove explosões de raios-gamma – e portanto, galáxias – com 5 bilhões de anos-luz de diâmetro. Os cientistas, liderados pelo Prof. Lajos Balazs, do Observatório Konkoloy, em Budapeste, reportou seu trabalho num artigo do Montlhy Notices of the Royal Astronomical Socitey.
Explosões de raios-Gamma as GRBs, são os eventos mais luminosos no universo, lançando o equivalente à energia que o Sol lança em 10 bilhões de anos em poucos segundos. Acredita-se que elas sejam o resultado do colapso de massivas estrelas em buracos negros. A grande luminosidade desses eventos, ajuda os astrônomos a mapearem o local de distantes galáxias, algo que a equipe explorou.
As GRBs que constituem o recém-descoberto anel foram observadas, usando uma grande variedade de telescópios, tanto em Terra como no espaço. Elas aparecem a uma distância muito similar de nós, cerca de 7 bilhões de anos-luz, num círculo de 36 graus através do nosso céu, ou o equivalente a mais de 70 vezes o diâmetro da Lua Cheia. Isso implica que o anel tem mais de 5 bilhões de anos-luz de diâmetro, e de acordo com o Professor Balazs, existe somente a probabilidade de 1 em 20000 das GRBs estarem nessa distribuição por coincidência.
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.
O telescópio de rastreio VISTA do ESO encontrou uma horda de galáxias massivas anteriormente ocultas por poeira, que existiram quando o Universo era ainda bebê. Ao descobrir e estudar uma grande quantidade deste tipo de galáxias, os astrônomos descobriram, exatamente e pela primeira vez, quando é que tais monstros apareceram pela primeira vez no Universo.
O simples fato de contar o número de galáxias que existem em determinada área do céu permite aos astrônomos testar teorias de formação e evolução galática. No entanto, uma tarefa aparentemente tão fácil torna-se mais difícil quando tentamos contar galáxias cada vez mais distantes e tênues e é mais complicada ainda devido ao fato das galáxias mais brilhantes e fáceis de observar — as mais massivas no Universo — se tornarem mais raras à medida que os astrônomos observam o passado do Universo, enquanto que as galáxias menos brilhantes, mas muito mais numerosas, são ainda mais difíceis de detectar.
Uma equipe de astrônomos liderada por Karina Caputi do Instituto Astronômico Kapteyn da Universidade de Groningen, descobriu muitas galáxias distantes que não tinham sido detectadas anteriormente. A equipe utilizou imagens do rastreioUltraVISTA, um dos seis projetos que usam o VISTA para mapear o céu no infravermelho próximo, e fez um censo das galáxias tênues quando a idade do Universo estava compreendida entre 0,75 e 2,1 bilhões de anos.
The network of filaments with embedded clusters surrounding voids, which has been seen in maps derived from
redshift surveys and reproduced in simulations, has been referred to as the cosmic web. A complementary
description is provided by considering the shear in the velocity field of galaxies. The eigenvalues of the shear
provide information regarding whether or not a region is collapsing in three dimensions, which is the condition for
a knot, expanding in three dimensions, which is the condition for a void, or in the intermediate condition of a
filament or sheet. The structures that are quantitatively defined by the eigenvalues can be approximated by isocontours
that provide a visual representation of the cosmic velocity (V) web. The current application is based on
radial peculiar velocities from the Cosmicflows-2 collection of distances. The three-dimensional velocity field is
constructed using the Wiener filter methodology in the linear approximation. Eigenvalues of the velocity shear are
calculated at each point on a grid. Here, knots and filaments are visualized across a local domain of
diameter ~0.1c
A giant ring_like_structure_at_078_z_086_displayed_by_gr_bsSérgio Sacani
Uma equipe de astrônomos da Hungria e dos EUA descobriram o que parece ser a maior feição no universo observável: um anel de nove explosões de raios-gamma – e portanto, galáxias – com 5 bilhões de anos-luz de diâmetro. Os cientistas, liderados pelo Prof. Lajos Balazs, do Observatório Konkoloy, em Budapeste, reportou seu trabalho num artigo do Montlhy Notices of the Royal Astronomical Socitey.
Explosões de raios-Gamma as GRBs, são os eventos mais luminosos no universo, lançando o equivalente à energia que o Sol lança em 10 bilhões de anos em poucos segundos. Acredita-se que elas sejam o resultado do colapso de massivas estrelas em buracos negros. A grande luminosidade desses eventos, ajuda os astrônomos a mapearem o local de distantes galáxias, algo que a equipe explorou.
As GRBs que constituem o recém-descoberto anel foram observadas, usando uma grande variedade de telescópios, tanto em Terra como no espaço. Elas aparecem a uma distância muito similar de nós, cerca de 7 bilhões de anos-luz, num círculo de 36 graus através do nosso céu, ou o equivalente a mais de 70 vezes o diâmetro da Lua Cheia. Isso implica que o anel tem mais de 5 bilhões de anos-luz de diâmetro, e de acordo com o Professor Balazs, existe somente a probabilidade de 1 em 20000 das GRBs estarem nessa distribuição por coincidência.
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.
O telescópio de rastreio VISTA do ESO encontrou uma horda de galáxias massivas anteriormente ocultas por poeira, que existiram quando o Universo era ainda bebê. Ao descobrir e estudar uma grande quantidade deste tipo de galáxias, os astrônomos descobriram, exatamente e pela primeira vez, quando é que tais monstros apareceram pela primeira vez no Universo.
O simples fato de contar o número de galáxias que existem em determinada área do céu permite aos astrônomos testar teorias de formação e evolução galática. No entanto, uma tarefa aparentemente tão fácil torna-se mais difícil quando tentamos contar galáxias cada vez mais distantes e tênues e é mais complicada ainda devido ao fato das galáxias mais brilhantes e fáceis de observar — as mais massivas no Universo — se tornarem mais raras à medida que os astrônomos observam o passado do Universo, enquanto que as galáxias menos brilhantes, mas muito mais numerosas, são ainda mais difíceis de detectar.
Uma equipe de astrônomos liderada por Karina Caputi do Instituto Astronômico Kapteyn da Universidade de Groningen, descobriu muitas galáxias distantes que não tinham sido detectadas anteriormente. A equipe utilizou imagens do rastreioUltraVISTA, um dos seis projetos que usam o VISTA para mapear o céu no infravermelho próximo, e fez um censo das galáxias tênues quando a idade do Universo estava compreendida entre 0,75 e 2,1 bilhões de anos.
Is there an_exoplanet_in_the_solar_systemSérgio Sacani
We investigate the prospects for the capture of the proposed Planet 9 from other
stars in the Sun’s birth cluster. Any capture scenario must satisfy three conditions:
the encounter must be more distant than ∼ 150 au to avoid perturbing the Kuiper
belt; the other star must have a wide-orbit planet (a & 100 au); the planet must be
captured onto an appropriate orbit to sculpt the orbital distribution of wide-orbit
Solar System bodies. Here we use N-body simulations to show that these criteria may
be simultaneously satisfied. In a few percent of slow close encounters in a cluster,
bodies are captured onto heliocentric, Planet 9-like orbits. During the ∼ 100 Myr
cluster phase, many stars are likely to host planets on highly-eccentric orbits with
apastron distances beyond 100 au if Neptune-sized planets are common and susceptible
to planet–planet scattering. While the existence of Planet 9 remains unproven, we
consider capture from one of the Sun’s young brethren a plausible route to explain such
an object’s orbit. Capture appears to predict a large population of Trans-Neptunian
Objects (TNOs) whose orbits are aligned with the captured planet, and we propose
that different formation mechanisms will be distinguishable based on their imprint on
the distribution of TNOs
On some structural_features_of_the_metagalaxySérgio Sacani
Progress in a group of investigations designed
to discover some of the structural details in individual galaxies and in the
Metagalaxy is reported in the following pages.
(a) The first section is concerned with the distribution of cluster-type
Cepheids in high galactic latitude. To the 169 already known in latitudes,
greater than or equal to ± 20o
, the systematic variable star programme carried
on at Harvard has added 312, mostly fainter than magnitude 13-0. With
allowance for absorption and for uncertainties yet remaining in the mean
absolute magnitude of these stars, the thickness of the Milky Way, so far
as this type of star is concerned, is not less than twenty-five kiloparsecs ;
he extent of the Milky Way in its own plane, by the same criterion, is more
than thirty kiloparsecs, perhaps much more.
(b) The extent of the Milky Way in the anti-centre quadrant is considered
on the basis of classical and cluster-type Cepheids ; provisionally
it is found that the galactic system reaches to a distance of at least ten
kiloparsecs in longitude 150o
.
(r) More than six hundred new variables have been found in the Large
Magellanic Cloud and measured for position, ranges and median magnitudes ;
the frequency of periods is not unlike that for the classical Cepheids in the
galactic system ; the light curves also are comparable in all details. The
Magellanic Cepheids, like the galactic classical Cepheids, are concentrated
in regions of high star-density.
(d) Further study of the period-luminosity relation in the Large Magellanic
Cloud permits its revision and strengthening for the Cepheids of
highest absolute magnitude. An observed deviation from the relation
that had previously been found for the Small Cloud is probably to be
attributed to scale error in the magnitude system. No seriously disturbing
A 2 4_determination_of_the_local_value_of_the_hubble_constantSérgio Sacani
We use the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST) to
reduce the uncertainty in the local value of the Hubble constant from 3.3% to 2.4%.
The bulk of this improvement comes from new, near-infrared observations of Cepheid
variables in 11 host galaxies of recent type Ia supernovae (SNe Ia), more than doubling
the sample of reliable SNe Ia having a Cepheid-calibrated distance to a total of 19; these
in turn leverage the magnitude-redshift relation based on 300 SNe Ia at z <0.15. All
19 hosts as well as the megamaser system NGC4258 have been observed with WFC3
in the optical and near-infrared, thus nullifying cross-instrument zeropoint errors in the
relative distance estimates from Cepheids. Other noteworthy improvements include a
33% reduction in the systematic uncertainty in the maser distance to NGC4258, a larger
sample of Cepheids in the Large Magellanic Cloud (LMC), a more robust distance to
the LMC based on late-type detached eclipsing binaries (DEBs), HST observations of
Cepheids in M31, and new HST-based trigonometric parallaxes for Milky Way (MW)
Cepheids.
T he effect_of_orbital_configuration)_on_the_possible_climates_and_habitabili...Sérgio Sacani
As lower-mass stars often host multiple rocky planets, gravitational interactions among planets can have significant
effects on climate and habitability over long timescales. Here we explore a specific case, Kepler-62f (Borucki et al.,
2013), a potentially habitable planet in a five-planet system with a K2V host star. N-body integrations reveal the
stable range of initial eccentricities for Kepler-62f is 0.00 £ e £ 0.32, absent the effect of additional, undetected
planets. We simulate the tidal evolution of Kepler-62f in this range and find that, for certain assumptions, the planet
can be locked in a synchronous rotation state. Simulations using the 3-D Laboratoire de Me´te´orologie Dynamique
(LMD) Generic global climate model (GCM) indicate that the surface habitability of this planet is sensitive to
orbital configuration.With 3 bar of CO2 in its atmosphere, we find that Kepler-62f would only be warm enough for
surface liquid water at the upper limit of this eccentricity range, providing it has a high planetary obliquity
(between 60 and 90). A climate similar to that of modern-day Earth is possible for the entire range of stable
eccentricities if atmospheric CO2 is increased to 5 bar levels. In a low-CO2 case (Earth-like levels), simulations
with version 4 of the Community Climate System Model (CCSM4) GCM and LMD Generic GCM indicate that
increases in planetary obliquity and orbital eccentricity coupled with an orbital configuration that places the
summer solstice at or near pericenter permit regions of the planet with above-freezing surface temperatures. This
may melt ice sheets formed during colder seasons. If Kepler-62f is synchronously rotating and has an ocean, CO2
levels above 3 bar would be required to distribute enough heat to the nightside of the planet to avoid atmospheric
freeze-out and permit a large enough region of open water at the planet’s substellar point to remain stable. Overall,
we find multiple plausible combinations of orbital and atmospheric properties that permit surface liquid water on
Kepler-62f. Key Words: Extrasolar planets—Habitability—Planetary environments. Astrobiology 16, xxx–xxx.
DISCOVERY OF A GALAXY CLUSTER WITH A VIOLENTLY STARBURSTING CORE AT z = 2:506Sérgio Sacani
We report the discovery of a remarkable concentration of massive galaxies with extended X-ray
emission at zspec = 2:506, which contains 11 massive (M & 1011M) galaxies in the central 80kpc
region (11.6 overdensity). We have spectroscopically conrmed 17 member galaxies with 11 from CO
and the remaining ones from H. The X-ray luminosity, stellar mass content and velocity dispersion
all point to a collapsed, cluster-sized dark matter halo with mass M200c = 1013:90:2M, making it
the most distant X-ray-detected cluster known to date. Unlike other clusters discovered so far, this
structure is dominated by star-forming galaxies (SFGs) in the core with only 2 out of the 11 massive
galaxies classied as quiescent. The star formation rate (SFR) in the 80kpc core reaches 3400 M
yr 1 with a gas depletion time of 200 Myr, suggesting that we caught this cluster in rapid build-up
of a dense core. The high SFR is driven by both a high abundance of SFGs and a higher starburst
fraction ( 25%, compared to 3%-5% in the eld). The presence of both a collapsed, cluster-sized
halo and a predominant population of massive SFGs suggests that this structure could represent an
important transition phase between protoclusters and mature clusters. It provides evidence that the
main phase of massive galaxy passivization will take place after galaxies accrete onto the cluster,
providing new insights into massive cluster formation at early epochs. The large integrated stellar
mass at such high redshift challenges our understanding of massive cluster formation.
The canarias einstein_ring_a_newly_discovered_optical_einstein_ringSérgio Sacani
We report the discovery of an optical Einstein Ring in the Sculptor constellation,
IAC J010127-334319, in the vicinity of the Sculptor Dwarf Spheroidal Galaxy. It is
an almost complete ring ( 300◦) with a diameter of 4.5 arcsec. The discovery was
made serendipitously from inspecting Dark Energy Camera (DECam) archive imaging
data. Confirmation of the object nature has been obtained by deriving spectroscopic
redshifts for both components, lens and source, from observations at the 10.4 m Gran
Telescopio CANARIAS (GTC) with the spectrograph OSIRIS. The lens, a massive
early-type galaxy, has a redshift of z = 0.581 while the source is a starburst galaxy
with redshift of z = 1.165. The total enclosed mass that produces the lensing effect
has been estimated to be Mtot = (1.86 ± 0.23) · 1012M⊙.
We report the discovery of a new Kepler transiting circumbinary planet (CBP).
This latest addition to the still-small family of CBPs defies the current trend of known
short-period planets orbiting near the stability limit of binary stars. Unlike the previous
discoveries, the planet revolving around the eclipsing binary system Kepler-1647 has
a very long orbital period ( 1100 days) and was at conjunction only twice during
the Kepler mission lifetime. Due to the singular configuration of the system, Kepler-
1647b is not only the longest-period transiting CBP at the time of writing, but also one
of the longest-period transiting planets. With a radius of 1:060:01 RJup it is also the
largest CBP to date. The planet produced three transits in the light-curve of Kepler-
1647 (one of them during an eclipse, creating a syzygy) and measurably perturbed the
times of the stellar eclipses, allowing us to measure its mass to be 1:520:65 MJup.
The planet revolves around an 11-day period eclipsing binary consisting of two Solarmass
stars on a slightly inclined, mildly eccentric (ebin = 0:16), spin-synchronized
orbit. Despite having an orbital period three times longer than Earth’s, Kepler-1647b is
in the conservative habitable zone of the binary star throughout its orbit.
Extensive Noachian fluvial systems in Arabia Terra: Implications for early Ma...Sérgio Sacani
Valley networks are some of the strongest lines of evidence for
extensive fluvial activity on early (Noachian; >3.7 Ga) Mars. However,
their purported absence on certain ancient terrains, such as
Arabia Terra, is at variance with patterns of precipitation as predicted
by “warm and wet” climate models. This disagreement has contributed
to the development of an alternative “icy highlands” scenario,
whereby valley networks were formed by the melting of highland ice
sheets. Here, we show through regional mapping that Arabia Terra
shows evidence for extensive networks of sinuous ridges. We interpret
these ridge features as inverted fluvial channels that formed in
the Noachian, before being subject to burial and exhumation. The
inverted channels developed on extensive aggrading flood plains. As
the inverted channels are both sourced in, and traverse across, Arabia
Terra, their formation is inconsistent with discrete, localized sources
of water, such as meltwater from highland ice sheets. Our results are
instead more consistent with an early Mars that supported widespread
precipitation and runoff.
Predictions of the_atmospheric_composition_of_gj_1132_bSérgio Sacani
GJ 1132 b is a nearby Earth-sized exoplanet transiting an M dwarf, and is amongst the most highly
characterizable small exoplanets currently known. In this paper we study the interaction of a magma
ocean with a water-rich atmosphere on GJ 1132b and determine that it must have begun with more
than 5 wt% initial water in order to still retain a water-based atmosphere. We also determine the
amount of O2
that can build up in the atmosphere as a result of hydrogen dissociation and loss.
We find that the magma ocean absorbs at most ∼ 10% of the O2 produced, whereas more than
90% is lost to space through hydrodynamic drag. The most common outcome for GJ 1132 b from our
simulations is a tenuous atmosphere dominated by O2
, although for very large initial water abundances
atmospheres with several thousands of bars of O2
are possible. A substantial steam envelope would
indicate either the existence of an earlier H2
envelope or low XUV flux over the system’s lifetime. A
steam atmosphere would also imply the continued existence of a magma ocean on GJ 1132 b. Further
modeling is needed to study the evolution of CO2
or N2
-rich atmospheres on GJ 1132 b.
Beyond the Kuiper Belt Edge: New High Perihelion Trans-Neptunian Objects With...Sérgio Sacani
We are conducting a survey for distant solar system objects beyond the Kuiper
Belt edge ( 50 AU) with new wide-field cameras on the Subaru and CTIO tele-
scopes. We are interested in the orbits of objects that are decoupled from the
giant planet region in order to understand the structure of the outer solar sys-
tem, including whether a massive planet exists beyond a few hundred AU as first
reported in Trujillo and Sheppard (2014). In addition to discovering extreme
trans-Neptunian objects detailed elsewhere, we have found several objects with
high perihelia (q > 40 AU) that differ from the extreme and inner Oort cloud
objects due to their moderate semi-major axes (50 < a < 100 AU) and eccen-
tricities (e . 0.3). Newly discovered objects 2014 FZ71 and 2015 FJ345 have
the third and fourth highest perihelia known after Sedna and 2012 VP113, yet
their orbits are not nearly as eccentric or distant. We found several of these high
perihelion but moderate orbit objects and observe that they are mostly near Nep-
tune mean motion resonances and have significant inclinations (i > 20 degrees).
These moderate objects likely obtained their unusual orbits through combined
interactions with Neptune’s mean motion resonances and the Kozai resonance,
similar to the origin scenarios for 2004 XR190. We also find the distant 2008
ST291 has likely been modified by the MMR+KR mechanism through the 6:1
Neptune resonance. We discuss these moderately eccentric, distant objects along
with some other interesting low inclination outer classical belt objects like 2012
FH84 discovered in our ongoing survey.
Star formation at the smallest scales; A JWST study of the clump populations ...Sérgio Sacani
We present the clump populations detected in 18 lensed galaxies at redshifts 1 to 8.5 within the lensing cluster field SMACS0723.
The recent JWST Early Release Observations of this poorly known region of the sky have revealed numerous point-like sources
within and surrounding their host galaxies, undetected in the shallower HST images. We use JWST multiband photometry and
the lensing model of this galaxy cluster to estimate the intrinsic sizes and magnitudes of the stellar clumps. We derive optical
restframe effective radii from <10 to hundreds pc and masses ranging from ∼ 105
to 109 M, overlapping with massive star
clusters in the local universe. Clump ages range from 1 Myr to 1 Gyr. We compare the crossing time to the age of the clumps
and determine that between 45 and 60 % of the detected clumps are consistent with being gravitationally bound. On average,
the dearth of Gyr old clumps suggests that the dissolution time scales are shorter than 1 Gyr. We see a significant increase in the
luminosity (mass) surface density of the clumps with redshift. Clumps in reionisation era galaxies have stellar densities higher
than star clusters in the local universe. We zoom in into single galaxies at redshift < 6 and find for two galaxies, the Sparkler and
the Firework, that their star clusters/clumps show distinctive colour distributions and location surrounding their host galaxy that
are compatible with being accredited or formed during merger events. The ages of some of the compact clusters are between
1 and 4 Gyr, e.g., globular cluster precursors formed around 9-12 Gyr ago. Our study, conducted on a small sample of galaxies,
shows the potential of JWST observations for understanding the conditions under which star clusters form in rapidly evolving
galaxies.
A Chandra X-ray study of millisecond pulsars in the globular cluster Omega Ce...Sérgio Sacani
Millisecond pulsars (MSPs) are faint X-ray sources commonly observed in Galactic globular clusters (GCs). In this work, we
investigate 18 MSPs newly found in the GC Omega Centauri (𝜔 Cen) and search for their X-ray counterparts using Chandra
observations with a total exposure time of 290.9 ks. We identify confident X-ray counterparts for 11 of the MSPs, with 9 of
them newly identified in this work based on their positions, spectral properties, and X-ray colours. The X-ray spectra of 9 MSPs
are well described by a neutron star hydrogen atmosphere model, while 2 MSPs are well fitted by a power-law model. The
identified MSPs have X-ray luminosities ranging from 1.0 × 1030 erg s−1
to 1.4 × 1031 erg s−1
. Additionally, for population
comparison purposes, we study the X-ray counterpart to MSP E in the GC M71, and find its X-ray spectrum is well described
by blackbody-like models with a luminosity of 1.9 × 1030 erg s−1
. We investigate the empirical correlations between X-ray
luminosities and minimum companion masses, as well as mass functions, of spider pulsars. Clear correlations are observed, with
best-fit functions of log10 𝐿𝑋 = (1.0 ± 0.1) log10 𝑀𝑐,𝑚𝑖𝑛 + (32.5 ± 0.2) and log10 𝐿𝑋 = (0.35 ± 0.04) log10 MF + (32.71 ± 0.20),
respectively, with an intrinsic scatter of log10 𝐿𝑋 of ∼0.3, where 𝐿𝑋 is the 0.5–10 keV X-ray luminosity, 𝑀𝑐,𝑚𝑖𝑛 is the minimum
companion mass, and MF represents the mass function, in solar masses.
Is there an_exoplanet_in_the_solar_systemSérgio Sacani
We investigate the prospects for the capture of the proposed Planet 9 from other
stars in the Sun’s birth cluster. Any capture scenario must satisfy three conditions:
the encounter must be more distant than ∼ 150 au to avoid perturbing the Kuiper
belt; the other star must have a wide-orbit planet (a & 100 au); the planet must be
captured onto an appropriate orbit to sculpt the orbital distribution of wide-orbit
Solar System bodies. Here we use N-body simulations to show that these criteria may
be simultaneously satisfied. In a few percent of slow close encounters in a cluster,
bodies are captured onto heliocentric, Planet 9-like orbits. During the ∼ 100 Myr
cluster phase, many stars are likely to host planets on highly-eccentric orbits with
apastron distances beyond 100 au if Neptune-sized planets are common and susceptible
to planet–planet scattering. While the existence of Planet 9 remains unproven, we
consider capture from one of the Sun’s young brethren a plausible route to explain such
an object’s orbit. Capture appears to predict a large population of Trans-Neptunian
Objects (TNOs) whose orbits are aligned with the captured planet, and we propose
that different formation mechanisms will be distinguishable based on their imprint on
the distribution of TNOs
On some structural_features_of_the_metagalaxySérgio Sacani
Progress in a group of investigations designed
to discover some of the structural details in individual galaxies and in the
Metagalaxy is reported in the following pages.
(a) The first section is concerned with the distribution of cluster-type
Cepheids in high galactic latitude. To the 169 already known in latitudes,
greater than or equal to ± 20o
, the systematic variable star programme carried
on at Harvard has added 312, mostly fainter than magnitude 13-0. With
allowance for absorption and for uncertainties yet remaining in the mean
absolute magnitude of these stars, the thickness of the Milky Way, so far
as this type of star is concerned, is not less than twenty-five kiloparsecs ;
he extent of the Milky Way in its own plane, by the same criterion, is more
than thirty kiloparsecs, perhaps much more.
(b) The extent of the Milky Way in the anti-centre quadrant is considered
on the basis of classical and cluster-type Cepheids ; provisionally
it is found that the galactic system reaches to a distance of at least ten
kiloparsecs in longitude 150o
.
(r) More than six hundred new variables have been found in the Large
Magellanic Cloud and measured for position, ranges and median magnitudes ;
the frequency of periods is not unlike that for the classical Cepheids in the
galactic system ; the light curves also are comparable in all details. The
Magellanic Cepheids, like the galactic classical Cepheids, are concentrated
in regions of high star-density.
(d) Further study of the period-luminosity relation in the Large Magellanic
Cloud permits its revision and strengthening for the Cepheids of
highest absolute magnitude. An observed deviation from the relation
that had previously been found for the Small Cloud is probably to be
attributed to scale error in the magnitude system. No seriously disturbing
A 2 4_determination_of_the_local_value_of_the_hubble_constantSérgio Sacani
We use the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope (HST) to
reduce the uncertainty in the local value of the Hubble constant from 3.3% to 2.4%.
The bulk of this improvement comes from new, near-infrared observations of Cepheid
variables in 11 host galaxies of recent type Ia supernovae (SNe Ia), more than doubling
the sample of reliable SNe Ia having a Cepheid-calibrated distance to a total of 19; these
in turn leverage the magnitude-redshift relation based on 300 SNe Ia at z <0.15. All
19 hosts as well as the megamaser system NGC4258 have been observed with WFC3
in the optical and near-infrared, thus nullifying cross-instrument zeropoint errors in the
relative distance estimates from Cepheids. Other noteworthy improvements include a
33% reduction in the systematic uncertainty in the maser distance to NGC4258, a larger
sample of Cepheids in the Large Magellanic Cloud (LMC), a more robust distance to
the LMC based on late-type detached eclipsing binaries (DEBs), HST observations of
Cepheids in M31, and new HST-based trigonometric parallaxes for Milky Way (MW)
Cepheids.
T he effect_of_orbital_configuration)_on_the_possible_climates_and_habitabili...Sérgio Sacani
As lower-mass stars often host multiple rocky planets, gravitational interactions among planets can have significant
effects on climate and habitability over long timescales. Here we explore a specific case, Kepler-62f (Borucki et al.,
2013), a potentially habitable planet in a five-planet system with a K2V host star. N-body integrations reveal the
stable range of initial eccentricities for Kepler-62f is 0.00 £ e £ 0.32, absent the effect of additional, undetected
planets. We simulate the tidal evolution of Kepler-62f in this range and find that, for certain assumptions, the planet
can be locked in a synchronous rotation state. Simulations using the 3-D Laboratoire de Me´te´orologie Dynamique
(LMD) Generic global climate model (GCM) indicate that the surface habitability of this planet is sensitive to
orbital configuration.With 3 bar of CO2 in its atmosphere, we find that Kepler-62f would only be warm enough for
surface liquid water at the upper limit of this eccentricity range, providing it has a high planetary obliquity
(between 60 and 90). A climate similar to that of modern-day Earth is possible for the entire range of stable
eccentricities if atmospheric CO2 is increased to 5 bar levels. In a low-CO2 case (Earth-like levels), simulations
with version 4 of the Community Climate System Model (CCSM4) GCM and LMD Generic GCM indicate that
increases in planetary obliquity and orbital eccentricity coupled with an orbital configuration that places the
summer solstice at or near pericenter permit regions of the planet with above-freezing surface temperatures. This
may melt ice sheets formed during colder seasons. If Kepler-62f is synchronously rotating and has an ocean, CO2
levels above 3 bar would be required to distribute enough heat to the nightside of the planet to avoid atmospheric
freeze-out and permit a large enough region of open water at the planet’s substellar point to remain stable. Overall,
we find multiple plausible combinations of orbital and atmospheric properties that permit surface liquid water on
Kepler-62f. Key Words: Extrasolar planets—Habitability—Planetary environments. Astrobiology 16, xxx–xxx.
DISCOVERY OF A GALAXY CLUSTER WITH A VIOLENTLY STARBURSTING CORE AT z = 2:506Sérgio Sacani
We report the discovery of a remarkable concentration of massive galaxies with extended X-ray
emission at zspec = 2:506, which contains 11 massive (M & 1011M) galaxies in the central 80kpc
region (11.6 overdensity). We have spectroscopically conrmed 17 member galaxies with 11 from CO
and the remaining ones from H. The X-ray luminosity, stellar mass content and velocity dispersion
all point to a collapsed, cluster-sized dark matter halo with mass M200c = 1013:90:2M, making it
the most distant X-ray-detected cluster known to date. Unlike other clusters discovered so far, this
structure is dominated by star-forming galaxies (SFGs) in the core with only 2 out of the 11 massive
galaxies classied as quiescent. The star formation rate (SFR) in the 80kpc core reaches 3400 M
yr 1 with a gas depletion time of 200 Myr, suggesting that we caught this cluster in rapid build-up
of a dense core. The high SFR is driven by both a high abundance of SFGs and a higher starburst
fraction ( 25%, compared to 3%-5% in the eld). The presence of both a collapsed, cluster-sized
halo and a predominant population of massive SFGs suggests that this structure could represent an
important transition phase between protoclusters and mature clusters. It provides evidence that the
main phase of massive galaxy passivization will take place after galaxies accrete onto the cluster,
providing new insights into massive cluster formation at early epochs. The large integrated stellar
mass at such high redshift challenges our understanding of massive cluster formation.
The canarias einstein_ring_a_newly_discovered_optical_einstein_ringSérgio Sacani
We report the discovery of an optical Einstein Ring in the Sculptor constellation,
IAC J010127-334319, in the vicinity of the Sculptor Dwarf Spheroidal Galaxy. It is
an almost complete ring ( 300◦) with a diameter of 4.5 arcsec. The discovery was
made serendipitously from inspecting Dark Energy Camera (DECam) archive imaging
data. Confirmation of the object nature has been obtained by deriving spectroscopic
redshifts for both components, lens and source, from observations at the 10.4 m Gran
Telescopio CANARIAS (GTC) with the spectrograph OSIRIS. The lens, a massive
early-type galaxy, has a redshift of z = 0.581 while the source is a starburst galaxy
with redshift of z = 1.165. The total enclosed mass that produces the lensing effect
has been estimated to be Mtot = (1.86 ± 0.23) · 1012M⊙.
We report the discovery of a new Kepler transiting circumbinary planet (CBP).
This latest addition to the still-small family of CBPs defies the current trend of known
short-period planets orbiting near the stability limit of binary stars. Unlike the previous
discoveries, the planet revolving around the eclipsing binary system Kepler-1647 has
a very long orbital period ( 1100 days) and was at conjunction only twice during
the Kepler mission lifetime. Due to the singular configuration of the system, Kepler-
1647b is not only the longest-period transiting CBP at the time of writing, but also one
of the longest-period transiting planets. With a radius of 1:060:01 RJup it is also the
largest CBP to date. The planet produced three transits in the light-curve of Kepler-
1647 (one of them during an eclipse, creating a syzygy) and measurably perturbed the
times of the stellar eclipses, allowing us to measure its mass to be 1:520:65 MJup.
The planet revolves around an 11-day period eclipsing binary consisting of two Solarmass
stars on a slightly inclined, mildly eccentric (ebin = 0:16), spin-synchronized
orbit. Despite having an orbital period three times longer than Earth’s, Kepler-1647b is
in the conservative habitable zone of the binary star throughout its orbit.
Extensive Noachian fluvial systems in Arabia Terra: Implications for early Ma...Sérgio Sacani
Valley networks are some of the strongest lines of evidence for
extensive fluvial activity on early (Noachian; >3.7 Ga) Mars. However,
their purported absence on certain ancient terrains, such as
Arabia Terra, is at variance with patterns of precipitation as predicted
by “warm and wet” climate models. This disagreement has contributed
to the development of an alternative “icy highlands” scenario,
whereby valley networks were formed by the melting of highland ice
sheets. Here, we show through regional mapping that Arabia Terra
shows evidence for extensive networks of sinuous ridges. We interpret
these ridge features as inverted fluvial channels that formed in
the Noachian, before being subject to burial and exhumation. The
inverted channels developed on extensive aggrading flood plains. As
the inverted channels are both sourced in, and traverse across, Arabia
Terra, their formation is inconsistent with discrete, localized sources
of water, such as meltwater from highland ice sheets. Our results are
instead more consistent with an early Mars that supported widespread
precipitation and runoff.
Predictions of the_atmospheric_composition_of_gj_1132_bSérgio Sacani
GJ 1132 b is a nearby Earth-sized exoplanet transiting an M dwarf, and is amongst the most highly
characterizable small exoplanets currently known. In this paper we study the interaction of a magma
ocean with a water-rich atmosphere on GJ 1132b and determine that it must have begun with more
than 5 wt% initial water in order to still retain a water-based atmosphere. We also determine the
amount of O2
that can build up in the atmosphere as a result of hydrogen dissociation and loss.
We find that the magma ocean absorbs at most ∼ 10% of the O2 produced, whereas more than
90% is lost to space through hydrodynamic drag. The most common outcome for GJ 1132 b from our
simulations is a tenuous atmosphere dominated by O2
, although for very large initial water abundances
atmospheres with several thousands of bars of O2
are possible. A substantial steam envelope would
indicate either the existence of an earlier H2
envelope or low XUV flux over the system’s lifetime. A
steam atmosphere would also imply the continued existence of a magma ocean on GJ 1132 b. Further
modeling is needed to study the evolution of CO2
or N2
-rich atmospheres on GJ 1132 b.
Beyond the Kuiper Belt Edge: New High Perihelion Trans-Neptunian Objects With...Sérgio Sacani
We are conducting a survey for distant solar system objects beyond the Kuiper
Belt edge ( 50 AU) with new wide-field cameras on the Subaru and CTIO tele-
scopes. We are interested in the orbits of objects that are decoupled from the
giant planet region in order to understand the structure of the outer solar sys-
tem, including whether a massive planet exists beyond a few hundred AU as first
reported in Trujillo and Sheppard (2014). In addition to discovering extreme
trans-Neptunian objects detailed elsewhere, we have found several objects with
high perihelia (q > 40 AU) that differ from the extreme and inner Oort cloud
objects due to their moderate semi-major axes (50 < a < 100 AU) and eccen-
tricities (e . 0.3). Newly discovered objects 2014 FZ71 and 2015 FJ345 have
the third and fourth highest perihelia known after Sedna and 2012 VP113, yet
their orbits are not nearly as eccentric or distant. We found several of these high
perihelion but moderate orbit objects and observe that they are mostly near Nep-
tune mean motion resonances and have significant inclinations (i > 20 degrees).
These moderate objects likely obtained their unusual orbits through combined
interactions with Neptune’s mean motion resonances and the Kozai resonance,
similar to the origin scenarios for 2004 XR190. We also find the distant 2008
ST291 has likely been modified by the MMR+KR mechanism through the 6:1
Neptune resonance. We discuss these moderately eccentric, distant objects along
with some other interesting low inclination outer classical belt objects like 2012
FH84 discovered in our ongoing survey.
Star formation at the smallest scales; A JWST study of the clump populations ...Sérgio Sacani
We present the clump populations detected in 18 lensed galaxies at redshifts 1 to 8.5 within the lensing cluster field SMACS0723.
The recent JWST Early Release Observations of this poorly known region of the sky have revealed numerous point-like sources
within and surrounding their host galaxies, undetected in the shallower HST images. We use JWST multiband photometry and
the lensing model of this galaxy cluster to estimate the intrinsic sizes and magnitudes of the stellar clumps. We derive optical
restframe effective radii from <10 to hundreds pc and masses ranging from ∼ 105
to 109 M, overlapping with massive star
clusters in the local universe. Clump ages range from 1 Myr to 1 Gyr. We compare the crossing time to the age of the clumps
and determine that between 45 and 60 % of the detected clumps are consistent with being gravitationally bound. On average,
the dearth of Gyr old clumps suggests that the dissolution time scales are shorter than 1 Gyr. We see a significant increase in the
luminosity (mass) surface density of the clumps with redshift. Clumps in reionisation era galaxies have stellar densities higher
than star clusters in the local universe. We zoom in into single galaxies at redshift < 6 and find for two galaxies, the Sparkler and
the Firework, that their star clusters/clumps show distinctive colour distributions and location surrounding their host galaxy that
are compatible with being accredited or formed during merger events. The ages of some of the compact clusters are between
1 and 4 Gyr, e.g., globular cluster precursors formed around 9-12 Gyr ago. Our study, conducted on a small sample of galaxies,
shows the potential of JWST observations for understanding the conditions under which star clusters form in rapidly evolving
galaxies.
A Chandra X-ray study of millisecond pulsars in the globular cluster Omega Ce...Sérgio Sacani
Millisecond pulsars (MSPs) are faint X-ray sources commonly observed in Galactic globular clusters (GCs). In this work, we
investigate 18 MSPs newly found in the GC Omega Centauri (𝜔 Cen) and search for their X-ray counterparts using Chandra
observations with a total exposure time of 290.9 ks. We identify confident X-ray counterparts for 11 of the MSPs, with 9 of
them newly identified in this work based on their positions, spectral properties, and X-ray colours. The X-ray spectra of 9 MSPs
are well described by a neutron star hydrogen atmosphere model, while 2 MSPs are well fitted by a power-law model. The
identified MSPs have X-ray luminosities ranging from 1.0 × 1030 erg s−1
to 1.4 × 1031 erg s−1
. Additionally, for population
comparison purposes, we study the X-ray counterpart to MSP E in the GC M71, and find its X-ray spectrum is well described
by blackbody-like models with a luminosity of 1.9 × 1030 erg s−1
. We investigate the empirical correlations between X-ray
luminosities and minimum companion masses, as well as mass functions, of spider pulsars. Clear correlations are observed, with
best-fit functions of log10 𝐿𝑋 = (1.0 ± 0.1) log10 𝑀𝑐,𝑚𝑖𝑛 + (32.5 ± 0.2) and log10 𝐿𝑋 = (0.35 ± 0.04) log10 MF + (32.71 ± 0.20),
respectively, with an intrinsic scatter of log10 𝐿𝑋 of ∼0.3, where 𝐿𝑋 is the 0.5–10 keV X-ray luminosity, 𝑀𝑐,𝑚𝑖𝑛 is the minimum
companion mass, and MF represents the mass function, in solar masses.
A 17 billion_solar_mass_black_hole_in_a_group_galaxy_with_a_difuse_coreSérgio Sacani
Quasars are associated with and powered by the accretion of
material onto massive black holes; the detection of highly luminous
quasars with redshifts greater than z = 6 suggests that black holes of
up to ten billion solar masses already existed 13 billion years ago1.
Two possible present-day ‘dormant’ descendants of this population
of ‘active’ black holes have been found2 in the galaxies NGC 3842
and NGC 4889 at the centres of the Leo and Coma galaxy clusters,
which together form the central region of the Great Wall3—the
largest local structure of galaxies. The most luminous quasars,
however, are not confined to such high-density regions of the
early Universe4,5; yet dormant black holes of this high mass have
not yet been found outside of modern-day rich clusters. Here we
report observations of the stellar velocity distribution in the galaxy
NGC 1600—a relatively isolated elliptical galaxy near the centre
of a galaxy group at a distance of 64 megaparsecs from Earth. We
use orbit superposition models to determine that the black hole at
the centre of NGC 1600 has a mass of 17 billion solar masses. The
spatial distribution of stars near the centre of NGC 1600 is rather
diffuse. We find that the region of depleted stellar density in the
cores of massive elliptical galaxies extends over the same radius as
the gravitational sphere of influence of the central black holes, and
interpret this as the dynamical imprint of the black holes.
The most luminous_galaxies_discovered_by_wiseSérgio Sacani
Artigo descreve estudo feito por astrônomos e com a ajuda da sonda WISE da NASA para identificar as galáxias do tipo ELIRGs, entre elas a mais luminosa galáxia do universo, com um buraco negro gigantesco em seu interior e localizada a cerca de 12.8 bilhões de anos de distância da Terra.
Black-hole-regulated star formation in massive galaxiesSérgio Sacani
Supermassive black holes, with masses more than a million
times that of the Sun, seem to inhabit the centres of all massive
galaxies1,2
. Cosmologically motivated theories of galaxy formation
require feedback from these supermassive black holes to regulate
star formation3
. In the absence of such feedback, state-of-the-art
numerical simulations fail to reproduce the number density and
properties of massive galaxies in the local Universe4–6. There
is, however, no observational evidence of this strongly coupled
coevolution between supermassive black holes and star formation,
impeding our understanding of baryonic processes within galaxies.
Here we report that the star formation histories of nearby massive
galaxies, as measured from their integrated optical spectra, depend
on the mass of the central supermassive black hole. Our results
indicate that the black-hole mass scales with the gas cooling rate
in the early Universe. The subsequent quenching of star formation
takes place earlier and more efficiently in galaxies that host highermass
central black holes. The observed relation between black-hole
mass and star formation efficiency applies to all generations of
stars formed throughout the life of a galaxy, revealing a continuous
interplay between black-hole activity and baryon cooling.
Exploring the nature and synchronicity of early cluster formation in the Larg...Sérgio Sacani
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.
DYNAMICAL ANALYSIS OF THE DARK MATTER AND CENTRAL BLACK HOLE MASS IN THE DWAR...Sérgio Sacani
We measure the central kinematics for the dwarf spheroidal galaxy Leo I using integrated-light measurements and
previously published data. We find a steady rise in the velocity dispersion from 30000 into the center. The integratedlight kinematics provide a velocity dispersion of 11.76±0.66 km s−1
inside 7500. After applying appropriate corrections
to crowding in the central regions, we achieve consistent velocity dispersion values using velocities from individual stars.
Crowding corrections need to be applied when targeting individual stars in high density stellar environments. From
integrated light, we measure the surface brightness profile and find a shallow cusp towards the center. Axisymmetric,
orbit-based models measure the stellar mass-to-light ratio, black hole mass and parameters for a dark matter halo. At
large radii it is important to consider possible tidal effects from the Milky Way so we include a variety of assumptions
regarding the tidal radius. For every set of assumptions, models require a central black hole consistent with a mass
3.3 ± 2×106 M. The no-black-hole case for any of our assumptions is excluded at over 95% significance, with
6.4 < ∆χ
2 < 14. A black hole of this mass would have significant effect on dwarf galaxy formation and evolution.
The dark halo parameters are heavily affected by the assumptions for the tidal radii, with the circular velocity only
constrained to be above 30 km s−1
. Reasonable assumptions for the tidal radius result in stellar orbits consistent with
an isotropic distribution in the velocities. These more realistic models only show strong constraints for the mass of
the central black hole.
We report the discovery of spiral galaxies that are as optically luminous as elliptical brightest cluster
galaxies, with r-band monochromatic luminosity Lr = 8 14L (4:3 7:5 1044 erg s 1). These
super spiral galaxies are also giant and massive, with diameter D = 57 134 kpc and stellar mass
Mstars = 0:3 3:4 1011M. We nd 53 super spirals out of a complete sample of 1616 SDSS
galaxies with redshift z < 0:3 and Lr > 8L. The closest example is found at z = 0:089. We use
existing photometry to estimate their stellar masses and star formation rates (SFRs). The SDSS
and WISE colors are consistent with normal star-forming spirals on the blue sequence. However, the
extreme masses and rapid SFRs of 5 65M yr 1 place super spirals in a sparsely populated region
of parameter space, above the star-forming main sequence of disk galaxies. Super spirals occupy a
diverse range of environments, from isolation to cluster centers. We nd four super spiral galaxy
systems that are late-stage major mergers{a possible clue to their formation. We suggest that super
spirals are a remnant population of unquenched, massive disk galaxies. They may eventually become
massive lenticular galaxies after they are cut o from their gas supply and their disks fade.
An excess of_dusty_starbusts_related_to_the_spiderweb_galaxySérgio Sacani
Artigo que descreve as últimas observações do APEX revelando como se dá a formação de estrelas e a construção do Aglomerado de Galáxias da Teia de Aranha.
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.
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
An almost dark galaxy with the mass of the Small Magellanic CloudSérgio Sacani
Almost Dark Galaxies are objects that have eluded detection by traditional surveys such as the Sloan Digital Sky Survey (SDSS). The
low surface brightness of these galaxies (µr(0)> 26 mag/arcsec2
), and hence their low surface stellar mass density (a few solar masses
per pc2 or less), suggests that the energy density released by baryonic feedback mechanisms is inefficient in modifying the distribution
of the dark matter halos they inhabit. For this reason, almost dark galaxies are particularly promising for probing the microphysical
nature of dark matter. In this paper, we present the serendipitous discovery of Nube, an almost dark galaxy with < µV >e∼ 26.7
mag/arcsec2
. The galaxy was identified using deep optical imaging from the IAC Stripe82 Legacy Project. Follow-up observations
with the 100m Green Bank Telescope strongly suggest that the galaxy is at a distance of 107 Mpc. Ultra-deep multi-band observations
with the 10.4m Gran Telescopio Canarias favour an age of ∼ 10 Gyr and a metallicity of [Fe/H]∼ −1.1. With a stellar mass of ∼ 4×108
M⊙ and a half-mass radius of Re = 6.9 kpc (corresponding to an effective surface density of < Σ >e∼ 0.9 M⊙/pc2
), Nube is the most
massive and extended object of its kind discovered so far. The galaxy is ten times fainter and has an effective radius three times larger
than typical ultra-diffuse galaxies with similar stellar masses. Galaxies with comparable effective surface brightness within the Local
Group have very low mass (tens of 105 M⊙) and compact structures (effective radius Re < 1 kpc). Current cosmological simulations
within the cold dark matter scenario, including baryonic feedback, do not reproduce the structural properties of Nube. However, its
highly extended and flattened structure is consistent with a scenario where the dark matter particles are ultra-light axions with a mass
of mB=(0.8
+0.4
−0.2
)×10−23 eV
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.
Similar to A population of faint low surface brightness galaxies in the Perseus cluster core (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
A brief information about the SCOP protein database used in bioinformatics.
The Structural Classification of Proteins (SCOP) database is a comprehensive and authoritative resource for the structural and evolutionary relationships of proteins. It provides a detailed and curated classification of protein structures, grouping them into families, superfamilies, and folds based on their structural and sequence similarities.
Slide 1: Title Slide
Extrachromosomal Inheritance
Slide 2: Introduction to Extrachromosomal Inheritance
Definition: Extrachromosomal inheritance refers to the transmission of genetic material that is not found within the nucleus.
Key Components: Involves genes located in mitochondria, chloroplasts, and plasmids.
Slide 3: Mitochondrial Inheritance
Mitochondria: Organelles responsible for energy production.
Mitochondrial DNA (mtDNA): Circular DNA molecule found in mitochondria.
Inheritance Pattern: Maternally inherited, meaning it is passed from mothers to all their offspring.
Diseases: Examples include Leber’s hereditary optic neuropathy (LHON) and mitochondrial myopathy.
Slide 4: Chloroplast Inheritance
Chloroplasts: Organelles responsible for photosynthesis in plants.
Chloroplast DNA (cpDNA): Circular DNA molecule found in chloroplasts.
Inheritance Pattern: Often maternally inherited in most plants, but can vary in some species.
Examples: Variegation in plants, where leaf color patterns are determined by chloroplast DNA.
Slide 5: Plasmid Inheritance
Plasmids: Small, circular DNA molecules found in bacteria and some eukaryotes.
Features: Can carry antibiotic resistance genes and can be transferred between cells through processes like conjugation.
Significance: Important in biotechnology for gene cloning and genetic engineering.
Slide 6: Mechanisms of Extrachromosomal Inheritance
Non-Mendelian Patterns: Do not follow Mendel’s laws of inheritance.
Cytoplasmic Segregation: During cell division, organelles like mitochondria and chloroplasts are randomly distributed to daughter cells.
Heteroplasmy: Presence of more than one type of organellar genome within a cell, leading to variation in expression.
Slide 7: Examples of Extrachromosomal Inheritance
Four O’clock Plant (Mirabilis jalapa): Shows variegated leaves due to different cpDNA in leaf cells.
Petite Mutants in Yeast: Result from mutations in mitochondrial DNA affecting respiration.
Slide 8: Importance of Extrachromosomal Inheritance
Evolution: Provides insight into the evolution of eukaryotic cells.
Medicine: Understanding mitochondrial inheritance helps in diagnosing and treating mitochondrial diseases.
Agriculture: Chloroplast inheritance can be used in plant breeding and genetic modification.
Slide 9: Recent Research and Advances
Gene Editing: Techniques like CRISPR-Cas9 are being used to edit mitochondrial and chloroplast DNA.
Therapies: Development of mitochondrial replacement therapy (MRT) for preventing mitochondrial diseases.
Slide 10: Conclusion
Summary: Extrachromosomal inheritance involves the transmission of genetic material outside the nucleus and plays a crucial role in genetics, medicine, and biotechnology.
Future Directions: Continued research and technological advancements hold promise for new treatments and applications.
Slide 11: Questions and Discussion
Invite Audience: Open the floor for any questions or further discussion on the topic.
Seminar of U.V. Spectroscopy by SAMIR PANDASAMIR PANDA
Spectroscopy is a branch of science dealing the study of interaction of electromagnetic radiation with matter.
Ultraviolet-visible spectroscopy refers to absorption spectroscopy or reflect spectroscopy in the UV-VIS spectral region.
Ultraviolet-visible spectroscopy is an analytical method that can measure the amount of light received by the analyte.
2. 2 Wittmann et al.
large diameter (10 000 pc), low central surface brightness
(≥ 25 B mag arcsec−2) galaxy, that comes in both early (i.e.,
dE) and late (i.e., Im V) types’ (Sandage & Binggeli 1984).
Further Virgo cluster galaxies of dwarf stellar mass but with
unusually large size and faint surface brightness were de-
scribed by Impey et al. (1988), and some similar objects
were discovered in the Fornax cluster by Ferguson & Sandage
(1988) and Bothun et al. (1991). Three decades later, galax-
ies in the same general parameter range were dubbed ‘ultra-
diffuse galaxies’ by van Dokkum et al. (2015a).
In the Coma cluster, a large number of over 700 very
faint candidate member galaxies with total magnitudes
MB > −13 mag, half-light radii 0.2 < r50 < 0.7 kpc and cen-
tral surface brightnesses as low as µB,0 = 27 mag arcsec−2
were identified by Adami et al. (2006). In the brighter and
overlapping magnitude range −11 Mg −16 mag van
Dokkum et al. (2015a) and Koda et al. (2015) reported
numerous LSB candidates with µg,0 ≥ 24 mag arcsec−2 and
half-light radii up to 5 kpc in Coma, of which five large ob-
jects with r50 3 kpc are spectroscopically confirmed cluster
members (van Dokkum et al. 2015b; Kadowaki et al. 2017).
The Virgo cluster study of Mihos et al. (2015, 2017) revealed
four LSB candidates with even lower central surface bright-
nesses of µV,0 ∼ 27 mag arcsec−2 and half-light radii as large
as 10 kpc. In the Fornax cluster an abundant population of
faint LSB galaxies with µr,0 ≥ 23 mag arcsec−2 were cata-
logued by Mu˜noz et al. (2015) and Venhola et al. (2017), of
which a few have r50 > 3 kpc (Venhola et al. 2017). Several
such objects in different environments were also reported by
Dunn (2010).
Although LSB galaxies have now been detected in large
numbers, their origin remains a puzzle. Especially the abun-
dant existence of LSB galaxies of dwarf stellar mass in galaxy
clusters raised the question how these low stellar density
systems could survive in the tidal field of such dense en-
vironments. For example, van Dokkum et al. (2015a) did
not report any signs of distortions for the faint LSB can-
didates identified in the Coma cluster. Other cluster LSB
galaxies of dwarf luminosity harbour surprisingly large and
intact globular cluster (GC) systems (e.g. Beasley & Tru-
jillo 2016; Peng & Lim 2016). One explanation could be
that these galaxies are characterized by a very high dark
matter content that prevents disruption of their stellar com-
ponent. A similar interpretation was given by Penny et al.
(2009) for a population of remarkably round and undis-
torted dSphs in the Perseus cluster core. Dynamical anal-
yses of two faint LSB galaxies in the Coma and Virgo clus-
ter indeed revealed very high mass-to-light ratios on the or-
der of M/L = 50–100 within one half-light radius (Beasley
et al. 2016; van Dokkum et al. 2016). Similar or even higher
M/L ratios are also characteristic for Local Group dSphs
with MV > −10 mag or µV 50 > 25 mag arcsec−2 (cf. Mc-
Connachie 2012). On the other hand, Milgrom (2015) sug-
gested that within the MOND theory high M/L ratios could
also be explained if the LSB galaxies would contain yet un-
detected cluster baryonic dark matter.
However, apparently the above does not apply to all
faint cluster LSB galaxies. For example, two LSB galaxy
candidates of very low stellar density in the Virgo clus-
ter show possible signs of disruption (Mihos et al. 2015,
2017). One large LSB candidate of dwarf luminosity with
a very elongated shape and truncated light profile was also
reported in Fornax (Lisker et al. 2017), and several further
elongated large LSB candidates were described by Venhola
et al. (2017). In the Hydra I galaxy cluster, Koch et al.
(2012) identified a faint LSB galaxy with S-shaped morphol-
ogy, indicative of its ongoing tidal disruption. Also van der
Burg et al. (2016), who studied populations of faint LSB
candidates with r50 ≥ 1.5 kpc in eight clusters with redshifts
z = 0.044–0.063, reported a depletion of LSB galaxy candi-
dates in the cluster cores, based on number counts. Similarly,
the numerical simulations of Yozin & Bekki (2015) predict
the disruption of LSB galaxies that are on orbits with very
close clustercentric passages.
In this study, we aim to investigate the faint LSB galaxy
population of the Perseus cluster core. Perseus is a rich
galaxy cluster at a redshift of z = 0.0179 (Struble & Rood
1999). While its mass is in between the lower mass Virgo
and the higher mass Coma cluster, its core reaches a density
comparable to that of the Coma cluster. There are indica-
tions that Perseus is possibly more relaxed and evolved than
Coma (e.g. Forman & Jones 1982). For example Perseus only
has a single cD galaxy in its centre, while the core of Coma
harbours two large galaxies. On the other hand, Andreon
(1994) interpreted the ‘non-uniform distribution of morpho-
logical types’ in Perseus as an indication that this cluster
is not yet virialized and instead dynamically young. This
may be supported by the observation that on large scales
Perseus is not a spherically symmetric cluster like Coma,
but shows a projected chain of bright galaxies extending in
east–west direction that is offset from the symmetric X-ray
distribution.
While a significant number of regular dwarf galaxies
has already been identified in a smaller field of the cluster
core by Conselice et al. (2002, 2003), we focus on galaxies in
the same luminosity range with MV > −16 mag (correspond-
ing to stellar masses of M∗ 108 M ) but of fainter sur-
face brightness and thus lower stellar density. This is made
possible by our deep wide-field imaging data obtained with
the 4.2 m William Herschel Telescope (WHT) Prime Focus
Imaging Platform (PFIP), reaching a 5σ V-band depth of
about 27 mag arcsec−2. In this paper, we concentrate on LSB
galaxies with µV 50 ≥ 24.8 mag arcsec−2, which corresponds
to the currently often adopted surface brightness limit of
µg,0 ≥ 24 mag arcsec−2 for the so-called ‘ultra-diffuse galax-
ies’. While the definition of the latter refers to objects with
r50 > 1.5 kpc (e.g. van Dokkum et al. 2015a), we will not
apply any size criterion in this study and generally speak of
‘faint LSB galaxies’, or ‘LSB galaxies of dwarf stellar mass’.
Previous work on the low-mass galaxy population in Perseus
includes also the 29 dwarf galaxies studied by Penny et al.
(2009) and de Rijcke et al. (2009) in Hubble Space Telescope
(HST) imaging data, of which six fall within our considered
surface brightness range.
This paper is organized as follows: in Section 2, we de-
scribe the observations, data reduction and our final mosaic.
We outline the detection of the LSB sources in Section 3,
and specify their photometry in Section 4. We present our
results in Section 5, where we define our sample of LSB can-
didates, examine their spatial distribution in the cluster, dis-
cuss peculiar candidates and characterize their magnitude–
size–surface brightness distribution in comparison to LSB
candidates in the Coma cluster. We discuss our results in
Section 6, followed by our conclusions in Section 7. Through-
MNRAS 000, 1–16 (2017)
3. Low surface brightness galaxies in Perseus 3
out the paper, we assume a distance of 72.3 Mpc to the
Perseus cluster with a scale of 20.32 kpc arcmin−1 (Stru-
ble & Rood 1999, using the ‘cosmology-corrected’ quantities
from NED with H0 = 73.00 km s−1 Mpc−1, Ωmatter = 0.27,
Ωvacuum = 0.73).
2 THE DATA
We acquired deep V-band imaging data of the Perseus clus-
ter core with PFIP at the WHT through the Opticon pro-
gramme 2012B/045 (PI T. Lisker). The PFIP is an op-
tical wide-field imaging camera with a field of view of
16 × 16 arcmin2, corresponding to 325 × 325 kpc2 at the dis-
tance of Perseus. The observations were carried out 2012
November 12 and 13. We performed dithered observations
on three pointings across the cluster core, with individual
exposure times of 120 s. In total, 187 science exposures con-
tribute to the final mosaic.
We reduced the data mainly with the image reduction
pipeline THELI1 (Erben et al. 2005; Schirmer 2013), which is
especially designed to process wide-field imaging data. For
the data reduction each exposure was spatially split into two
frames, corresponding to the two detectors of the instru-
ment. All frames were overscan- and bias-corrected, as well
as flat fielded using twilight flats. To correct for remaining
large-scale intensity gradients that may still be imprinted
in the data after flat fielding, a master background, con-
taining only signal from the sky, was created. For the latter
the sources in all frames were masked, then the frames were
normalized and stacked. Assuming the background inhomo-
geneities are of additive nature, the master background was
subsequently subtracted from all frames. Since applying one
common master background was not sufficient to remove the
large-scale background variations from all frames, individual
background models were created in a next step.
The individual models are based on object-masked
frames, where the masked areas were interpolated based on
values from neighbouring unmasked pixels. The resulting
images were convolved with a Gaussian kernel with a full
width at half-maximum (FWHM) of 512 pixels. The indi-
vidual background models were subtracted from each frame.
We note that the applied filter kernel is large with respect
to the extent of our targets, which have typical half-light
radii on the order of 20–60 pixels. Then all frames were cal-
ibrated astrometrically and distortion corrected, using the
Sloan Digital Sky Survey Data Release 9 (SDSS-DR9) (Ahn
et al. 2012) as a reference catalogue. Finally the frames were
resampled and combined to a mosaic, where each frame was
weighted according to the square of its inverse sky noise.
In a second iteration of the reduction we improved the
individual background models of the frames that were con-
taminated through the extended haloes of the two bright-
est cluster galaxies. This optimization was done outside the
THELI pipeline, mainly using IRAF.2 Manually extending the
masks would have resulted in a very high fraction of masked
1 THELI GUI, version 2.6.2
2 IRAF is distributed by the National Optical Astronomy Obser-
vatory, which is operated by the Association of Universities for
Research in Astronomy (AURA) under a cooperative agreement
with the National Science Foundation.
pixels on the single frames. To avoid this, we modelled the
light distribution of both galaxies in the first iteration mo-
saic, using IRAF ellipse and bmodel. We then subtracted the
galaxy models from the distortion corrected frames before
generating new individual background models with THELI.
The new background models were then subtracted from the
original science frames, and combined to the second mosaic.
Lastly we corrected our mosaic for spatial zero-point
variations, again outside the THELI pipeline. After selecting
suitable stars in our mosaic using SExtractor (Bertin &
Arnouts 1996), we measured their magnitudes with the IRAF
task photometry on the individual flat fielded frames, before
any background model was subtracted. We calculated the
zero-point of each frame as median magnitude offset with
respect to the SDSS-DR9 catalogue, using the transforma-
tion equations from Jester et al. (2005). The zero-point vari-
ations are then given as the deviation of the magnitude off-
set of individual stars from the zero-point of the respective
frame. We rejected stars that deviate by more than 0.2 mag
from the zero-point of the respective frame and only consid-
ered stars with small magnitude errors in both the SDSS-
DR9 catalogue and the measurements with IRAF photome-
try, requiring ∆mag2
phot
+ ∆mag2
SDSS
< 0.05 mag. We then
established a two-dimensional map yielding the zero-point
variations across the detector by fitting a two-dimensional
surface to the zero-point variations obtained for all frames.
Finally, we divided each frame by this map, and repeated
the above described reduction steps leading to the final mo-
saic. The zero-point of the final mosaic is 26 mag, with a
mean variation of 0.02 mag with respect to the SDSS-DR9
catalogue.
Fig. 1 (left-hand panel) shows our final deep mosaic of
the Perseus cluster core (also Figs 3 and 4). It is not centred
directly on the brightest cluster galaxy NGC 1275, but on
a region including the chain of luminous galaxies that are
distributed to the west of it. The mosaic covers an area of
∼ 0.27 deg2 ( ˆ= 0.41 Mpc2), and extends to a clustercentric
distance of 0.57◦( ˆ= 0.70 Mpc2) from NGC 1275. This corre-
sponds to 29 per cent of the Perseus cluster virial radius for
Rvir = 2.44 Mpc (Mathews et al. 2006), or 39 per cent when
adopting Rvir = 1.79 Mpc (Simionescu et al. 2011). The mo-
saic reaches an image depth of 27 mag arcsec−2 in the V-band
at a signal-to-noise ratio of S/N = 1 per pixel, with a pixel
scale of 0.237 arcsec pixel−1. The corresponding 1σ and 5σ
depths are 28.6 and 26.8 mag arcsec−2, respectively. The im-
age depth varies across the mosaic, as can be seen in the
weight image (Fig. 1, right-hand panel). The average seeing
FWHM is 0.9 arcsec.
For the subsequent detection and photometry of low
surface brightness sources we created one copy of the mosaic
where we removed most of the sources with bright extended
haloes, including the largest cluster galaxies and the haloes
of foreground stars. We fitted the light profiles with IRAF
ellipse, generated models with IRAF bmodel and subtracted
them from the mosaic.
3 DETECTION
Motivated by the detection of faint LSB galaxy candidates in
the Virgo and Coma galaxy clusters by Mihos et al. (2015)
and van Dokkum et al. (2015a), we inserted LSB galaxy
MNRAS 000, 1–16 (2017)
4. 4 Wittmann et al.
Figure 1. Deep view of the Perseus cluster core. Left: V-band mosaic. The image dimensions are 0.58◦( ˆ= 0.71 Mpc at 72.3 Mpc) in
east–west and north–south direction. North is up and east is to the left. The two bright galaxies in the east are NGC 1275 and NGC 1272.
Right: corresponding weight image indicating the image depth in mag arcsec−2 at S/N=1 per pixel (see legend on the right-hand side).
The black boxes indicate how we divided the mosaic into different regions for the detection of LSB sources (see Section 3).
models in the same parameter range into our mosaic and
then searched systematically for similarly looking objects
in Perseus. We decided to search for LSB sources by eye,
since automatic detection algorithms often fail in reliably
detecting sources with very low S/N. We realized the models
with a one component S´ersic profile of S´ersic index n = 0.7–
1.2 that were convolved with a Gaussian kernel, adopting
our average seeing FWHM.
We generated a first set of 27 models in the parame-
ter range 24.6 ≤ µV 50 ≤ 27.8 mag arcsec−2, −14 ≥ MV ≥
−16.6 mag, and 2.1 ≤ r50 ≤ 9.7 kpc, assuming an average
foreground extinction of AV = 0.5 mag at the location of
Perseus. Among them are nine model types with different
magnitudes and half-light radii. For each model type we
generated two additional variants with altered position an-
gle and ellipticity, which results in slightly different surface
brightnesses. We created a second set of seven nearly round
(ellipticity = 0.1) models with µV 50 ≤ 26.0 mag arcsec−2
that extend the parameter range to smaller half-light radii
of 1.5 kpc and fainter magnitudes of −13.5 mag.
From the first model set, we always inserted 30–40 mod-
els of one type, i.e. with the same magnitude and half-light
radius but varying ellipticity, into one copy of the mosaic.
We generated two additional mosaic copies where we in-
serted the models from the second model set. We used these
copies only at a later stage to focus the detection especially
on smaller and fainter LSB sources that turned out to be
quite numerous based on the search using the first model
set. In total we inserted 305 models from the first model set
into nine different mosaic copies, and 56 models from the
second set into two further copies.
To facilitate the visual detection of LSB sources, we
used the mosaic variant where we previously fitted and sub-
tracted the light distribution of most of the extended sources
(see Section 2). To remove the remaining bright sources on
each copy of the mosaic, we ran SExtractor to detect all
sources with more than 10 pixels above a detection threshold
of 1.5 σ, and replaced the pixels above this threshold with
zero values, corresponding to the background level of our
mosaic. We then convolved the data with a circular Gaus-
sian kernel with σ = 1 pixel, and demagnified each copy by
a factor of 1.5. We further divided each mosaic copy into
four smaller regions of different image depth according to the
weight image (see Fig.1, right-hand panel). Finally two of us
independently searched visually for diffuse sources in each
copy, thereby detecting simultaneously the inserted models
and real LSB candidates, without knowing where the former
had been inserted. After removing sources that we identified
more than once in different copies of the same region, this re-
sulted in a preliminary sample of 214 LSB sources that were
identified by at least one of us, and for which we carried out
photometry (see Section 4).
We used the visually identified models from the first
model set to get a rough estimate on our detection rate (see
Fig. 2). We estimated the detection rate for each model type
as fraction of the total number of inserted models that were
visually identified. We find that the detection rate gener-
ally drops with surface brightness. We detected more than
90 per cent of all models with µV 50 < 25.5 mag arcsec−2, be-
tween 70 and 90 per cent of all models with 25.5 ≤ µV 50 <
27.0 mag arcsec−2, and about 50 per cent of all models with
µV 50 > 27.0 mag arcsec−2.3
The models with µV 50 < 27.0 mag arcsec−2 are in gen-
3 The given surface brightnesses refer to the average surface
MNRAS 000, 1–16 (2017)
5. Low surface brightness galaxies in Perseus 5
24.5 25.0 25.5 26.0 26.5 27.0 27.5 28.0
¡V¢50 (mag arcsec-2
)
10
0
10
1
r50(kpc)
detection rate ≥ 90 %
70 % ≤ detection rate < 90 %
detection rate = 50 %
Figure 2. Detection rates of visually identified model galaxies as
a function of half-light radius and surface brightness. The detec-
tion rates are based on 30–40 models of one type, with the same
half-light radius and magnitude, but varying ellipticity and thus
surface brightness, that were inserted into one copy of the mo-
saic, respectively. Models of the same type are connected through
dashed lines in the plot. The total number of inserted models is
305.
eral clearly visible in our data and the main reason for miss-
ing some of them seems to be related to overlap with brighter
sources. We estimated the area occupied by remaining bright
extended sources in our object-subtracted mosaic to be
12 per cent4, which compares to an average detection rate
of 90 per cent of all models with µV 50 < 27.0 mag arcsec−2.
Scatter in the trend of decreasing detection fraction with
surface brightness can both be caused by our approach of
visual source detection, as well as by the different overlap
fractions of the inserted models with brighter sources.5 The
detection rate of models with µV 50 < 27.0 mag arcsec−2 is
similar in all regions of our mosaic, even in the shallowest
region (Region 1; see Fig.1, right-hand panel). For models
with µV 50 > 27.0 mag arcsec−2 we find, however, a lower
detection rate in Region 1 and Region 2, compared to the
other two regions. While Region 1 is the shallowest region,
the lower detection rate in Region 2 might be related to the
higher galaxy density compared to the other regions.
4 PHOTOMETRY
Photometry of LSB sources is challenging and the measure-
ments suffer in general from higher uncertainties compared
to sources of brighter surface brightness. One reason for this
is that the radial flux profile of the former is characterized
brightness of the three model variants with different ellipticity,
and thus surface brightness, that exist per model type.
4 This accounts for all sources that were detected with SExtrac-
tor with more than 1000 connected pixels above a detection
threshold of 1.5 σ.
5 We note that the fraction of models whose centre overlaps with
one of the SExtractor-detected sources above 1.5 σ does not
exceed 12 per cent per model type.
by a larger fraction of flux at large radii, where the S/N
is typically very low. This also implies that contamination
from close neighbour sources and the presence of background
gradients is more severe for these objects. We quantify the
arising uncertainties in our data using inserted LSB galaxy
models (see Section 5.3).
We derived magnitudes and sizes from growth curves
through iterative ellipse fitting with IRAF ellipse, rather than
from fits to analytical models. The first step was to obtain a
first guess of the centre, ellipticity and position angle of all
sources. We used SExtractor to measure the parameters
of 131 objects that were detected with a detection thresh-
old of 1 σ (128 objects) or 0.8 σ (3 objects). For 83 objects
that were not detected with SExtractor or that had obvi-
ously wrong parameters we estimated their centre and shape
visually based on the Gaussian smoothed and demagnified
mosaic. Then we ran ellipse with fixed parameters, adopt-
ing the previously measured or estimated centres, elliptic-
ities and position angles. We chose a linear step-size of 5
pixels for consecutive isophotes. We used the first ellipse fit
results to generate two-dimensional brightness models with
IRAF bmodel that we subtracted from the fitted source.
The residual images served as a basis to create masks
of neighbouring sources from SExtractor segmentation
images. We ran SExtractor in two passes, one with a
minimum number of 28 connected pixels above a detection
threshold of 1 σ, the other with a lower detection threshold
of 0.6 σ and requiring a minimum number of 1000 connected
pixels. In both passes, we used SExtractor with the built-
in filtering prior to detection. We combined both segmen-
tation images and extended the masked areas by smooth-
ing with a Gaussian kernel. We ran ellipse in a second
pass with the masks to exclude that flux from neighbour-
ing sources contributes to the ellipse fits. From the second
iteration residual images we created improved masks where
the masked regions are somewhat larger. We unmasked the
centre of nucleated candidates and ellipse fit residuals when
necessary.
The next step was to determine the background level
from the third pass ellipse fit results using the improved
masks. Getting the background level right is a very subtle
task and the major source of the uncertainties in the magni-
tude and size measurements. Therefore, we determined the
background level for each of our detected LSB objects in-
dividually. We first measured the radial flux profiles out to
large radii (350 pixels) for each object. We then manually
adjusted the radius and width of the background annulus,
whose median flux we adopted as the background level. The
inner radius of the background annulus was set at the first
break in the flux profile where the intensity gradient signif-
icantly changes and the flux profile levels out. We set the
width of the annulus to 50 pixels. Its shape follows the el-
lipticity and position angle of the measured object.
Although all neighbour sources were carefully masked,
still some flux profiles show signs of contamination. Espe-
cially at larger radii where faint flux levels are reached, the
flux of the LSB source can be comparable to the flux of a
neighbour source that still extends beyond the masked area
(e.g. some very extended haloes of foreground stars or bright
cluster galaxies). Also background inhomogeneities remain-
ing in the data after the reduction can contaminate the flux
profiles. Possible contamination can become apparent in a
MNRAS 000, 1–16 (2017)
6. 6 Wittmann et al.
flux profile when, for example, the profile continues to de-
cline after the first break instead of levelling out to zero. In
this case we nevertheless set the inner radius of the back-
ground annulus to the first break in the profile, and eventu-
ally decrease its width to make sure that the flux profile is
flat in this region.
Even though we might truncate a galaxy at too high in-
tensity, resulting in a systematically fainter magnitude and
a smaller half-light radius, restricting the analysis to the
uncontaminated inner profile helps to preserve the true sur-
face brightnesses (see the right-hand panels in Fig. 6 and
Section 5.3). After subtracting the background offset, we
then obtained a first estimate of the magnitudes and sizes
by running ellipse in a fourth pass on the background cor-
rected images and taking into account the masked sources.
We determined the total flux from the cumulative flux pro-
file6 and derived the half-light radius along the semimajor
axis, as well as the mean effective surface brightness within
one half-light radius.
In the final iteration we measured the centre, ellipticity
and position angle of our LSB sources more accurately, us-
ing our first guess parameters as input values. We used IRAF
imcentroid to derive the centre, and calculated the ellipticity
and position angle from the image moments within a circular
area defined by our first-guess half-light radius. We also fur-
ther improved the masks by manually enlarging the masks
of extended neighbour sources with faint haloes.7 After that
we ran ellipse in a fifth pass with the new parameters and
masks to adjust the inner radius of the background annu-
lus. We adopted the new background level and derived the
final magnitudes, half-light radii and mean effective surface
brightnesses in a last pass of ellipse fitting. We corrected the
derived magnitudes for extinction, using the IRSA Galactic
Reddening and Extinction Calculator, with reddening maps
from Schlafly & Finkbeiner (2011). The average foreground
extinction of our measured sources is AV = 0.5 mag.
5 FAINT LSB GALAXIES IN THE PERSEUS
CLUSTER CORE
5.1 Sample
We define our sample of LSB galaxy candidates to include all
objects with µV 50 ≥ 24.8 mag arcsec−2. This corresponds
to the currently often adopted surface brightness limit of
µg,0 ≥ 24.0 mag arcsec−2 for ‘ultra-diffuse galaxies’ (e.g. van
Dokkum et al. 2015a), when assuming an exponential profile
with S´ersic n = 1 (cf. Graham & Driver 2005), g − r = 0.6
and using the transformation equations from Jester et al.
(2005). Of our preliminary sample, 133 objects fall into this
parameter range. We carefully examined all of them, both
6 We adopted the median of the cumulative fluxes TFLUX_E from
the ellipse fit tables, namely of the five isophotes between the
inner radius of the background annulus and 20 pixels further, as
an estimate of the total flux. Since ellipse does not account for
masked regions when calculating the total flux within an isophote,
we replaced the masked regions with values from the 2-D model
created with IRAF bmodel from the radial flux profile.
7 Using SAOImages DS9 (Joye & Mandel 2003) regions and IRAF
mskregions.
on the original as well as on the smoothed and demagnified
mosaic. We also compared them to an independent data set
of the Perseus cluster, obtained with WIYN/ODI in the g,r
and i filters (programme 15B-0808/5, PI: J. S. Gallagher).
Since the single-band images are shallower than our data,
we used the stacked g,r,i images for the comparison.
Based on a more detailed visual examination of their
morphology, we classified 82 of our candidates as likely
galaxies. They are characterized by a smooth morphology
and are confirmed in the independent data set. We classified
seven further candidates as possible galaxies (all of them are
shown in Fig. 3 in the bottom row). Three of them (candi-
dates 26, 31 and 44) are clearly visible in our data, but their
morphology does not appear very regular. Since these ob-
jects are also visible in the WIYN/ODI data, we rule out
that they are image artefacts. However a confusion with cir-
rus cannot be excluded (see Section 5.3). The four other
candidates (candidates 27, 49, 57 and 81) are classified as
possible galaxies since they are only barely visible in our
data, due to their low surface brightness or low S/N, and
are not confirmed in the shallower independent data set. We
rejected 44 LSB sources from our sample, since we cannot ex-
clude that these are remaining background inhomogeneities
from the reduction, or residuals from ellipse fitting of the
brighter galaxies. Most of them are of very diffuse nature
(80 per cent have µV 50 ≥ 26.5 mag arcsec−2) and often do
not have a smooth morphology.
Our final sample includes 89 LSB galaxy candidates in
the Perseus cluster core. We show our sample in Fig. 3 and
provide the photometric parameters in Table 1. We also
compare our sample to overlapping HST/ACS images, in
order to investigate whether some of our objects would clas-
sify as background sources, based on possible substructure
in the form of, e.g., spiral arms. Seven of our LSB candi-
dates fall on HST/ACS pointings, and none of them shows
signs of substructure. We therefore expect that the overall
contamination through background galaxies is low in our
sample, based on the morphological appearance in the HST
as well as in the WHT images and due to the location of
our sample in the core region rather than in the cluster
outskirts. Certain cluster membership can, however, only
be established through measurements of radial velocities.
The six brightest candidates in the HST/ACS images with
24.8 ≤ µV 50 ≤ 25.4 mag arcsec−2, as measured in our data,
were previously identified in Penny et al. (2009) (candidates
62, 64, 69, 70, 73 and 87). One of them (candidate 62) was
first catalogued by Conselice et al. (2002, 2003). The faintest
candidate, with µV 50 = 26.5 mag arcsec−2 (candidate 82),
is only barely visible in the HST/ACS images and was not
published previously.
5.2 Properties
Fig. 4 shows the spatial distribution of our sample of 89 faint
LSB galaxy candidates in the Perseus cluster core. The sam-
ple spans a range of 47 ≤ d ≤ 678 kpc in projected cluster-
centric distance, with respect to the cluster’s X-ray centre8
(Piffaretti et al. 2011). This corresponds to 0.02 − 0.28 Rvir
8 The X-ray centroid almost coincides with the optical location
of NGC 1275.
MNRAS 000, 1–16 (2017)
7. Low surface brightness galaxies in Perseus 7
Figure 3. Sample of faint LSB galaxy candidates in the Perseus cluster core. The first 82 panels show the LSB candidates in cutout
regions of our original data with a size of 21 × 21 arcsec2, respectively. The seven last panels in the bottom row show the LSB candidates
classified as possible galaxies (see Section 5.1). They are displayed in our smoothed and demagnified data in cutout regions with a size
of 53 × 53 arcsec2, respectively. The blue bar in each panel of the figure denotes a length of 3 kpc. The number in each panel corresponds
to the ID of the shown object given in Table 1. North is up and east is to the left.
MNRAS 000, 1–16 (2017)
9. Low surface brightness galaxies in Perseus 9
Table 1 – continued
ID R.A. Dec. µV 50 MV AV r50 Ellipticity
(J2000) (J2000) (mag arcsec−2) (mag) (mag) (kpc)
60 03 18 55.38 +41 17 50.0 25.8 -12.5 0.5 1.0 0.18
61 03 18 59.40 +41 25 15.4 26.0 -12.5 0.4 1.0 0.07
62 03 18 59.42 +41 31 18.7 25.4 -13.9 0.4 1.4 0.07
63 03 19 01.50 +41 38 59.0 25.8 -12.9 0.5 1.1 0.17
64 03 19 05.83 +41 32 34.4 24.8 -13.8 0.4 1.1 0.09
65 03 19 07.77 +41 27 12.1 24.8 -12.9 0.4 0.7 0.06
66 03 19 09.32 +41 41 51.7 25.9 -12.5 0.5 0.9 0.06
67 03 19 12.76 +41 43 30.0 25.2 -13.5 0.5 1.1 0.08
68 03 19 15.01 +41 22 31.7 25.1 -13.3 0.4 0.9 0.06
69 03 19 15.70 +41 30 34.6 25.1 -12.9 0.4 0.8 0.05
70 03 19 15.86 +41 31 05.8 25.2 -14.2 0.4 1.4 0.03
71 03 19 16.02 +41 45 45.9 26.1 -13.3 0.5 1.4 0.05
72 03 19 17.53 +41 12 41.3 26.7 -12.8 0.4 1.5 0.02
73 03 19 17.83 +41 33 48.4 24.9 -13.7 0.4 1.0 0.07
74 03 19 21.94 +41 27 22.5 24.9 -14.7 0.4 1.7 0.15
75 03 19 23.06 +41 23 16.8 26.3 -13.7 0.4 2.1 0.20
76 03 19 23.12 +41 38 58.7 26.0 -13.4 0.5 1.5 0.11
77 03 19 32.76 +41 36 12.8 25.7 -13.6 0.4 1.4 0.09
78 03 19 33.80 +41 36 32.5 24.8 -13.6 0.5 1.1 0.34
79 03 19 39.19 +41 12 05.6 25.4 -14.4 0.4 1.8 0.06
80 03 19 39.22 +41 13 43.5 26.3 -12.8 0.4 1.3 0.07
81 03 19 44.03 +41 39 18.4 26.9 -13.8 0.4 2.7 0.14
82 03 19 45.66 +41 28 07.3 26.1 -13.9 0.4 2.0 0.13
83 03 19 47.45 +41 44 09.3 26.0 -12.9 0.4 1.2 0.07
84 03 19 49.70 +41 43 42.6 24.8 -13.5 0.4 0.9 0.05
85 03 19 50.13 +41 24 56.3 25.5 -13.7 0.4 1.3 0.05
86 03 19 50.56 +41 15 33.4 25.6 -12.1 0.4 0.7 0.17
87 03 19 57.41 +41 29 31.2 25.0 -13.3 0.4 0.9 0.05
88 03 19 59.10 +41 18 33.1 24.8 -15.5 0.4 2.2 0.02
89 03 20 00.20 +41 17 05.1 25.7 -13.5 0.4 1.4 0.10
when assuming a virial radius of Rvir = 2.44 Mpc (Mathews
et al. 2006). About half of our sample is located closer than
330 kpc to the cluster centre.
We find three LSB candidates that appear to be asso-
ciated with structures resembling tidal streams (see Fig. 4,
right-hand panels). Candidate 44 seems to be embedded in
diffuse filaments, candidates 26 and 31 appear connected via
an arc-shaped stream. We find one further galaxy with tidal
tails (see Fig. 4, bottom left panel), which has a slightly
brighter surface brightness of µV 50 = 24.4 mag arcsec−2
and therefore was not included in our sample. We will
analyse faint cluster galaxies with brighter surface bright-
nesses in a future paper. It is noticeable that all four ob-
jects are confined within one region to the south–west of
the cluster centre, within a clustercentric distance range of
about 300−400 kpc. Also the peculiar more luminous galaxy
SA 0426-002 (cf. Conselice et al. 2002; Penny et al. 2014)
falls on our mosaic, which shows a disturbed morphology
with extended low surface brightness lobes (see Fig. 4, top
left panel).
We show the radial projected number density distri-
bution of our sample in Fig. 5. It was derived by dividing
the number of galaxies in radial bins of a width of 100 kpc
by the area of the respective bin that falls on our mo-
saic. The bins are centred on the Perseus X-ray centre. We
find that the number density is nearly constant for cluster-
centric distances r ≥ 100 kpc, but drops in the very centre at
r < 100 kpc,9 with a statistical significance of 2.8 σ with re-
spect to the average number density at larger radii. For com-
parison, a preliminary analysis showed that the distribution
of bright cluster members is consistent with the expectation
of being much more centrally concentrated.
Fig. 6 shows the magnitude–size and magnitude–surface
brightness distribution of our Perseus cluster LSB galaxy
sample. We include the Coma cluster LSB galaxies and can-
didates from van Dokkum et al. (2015a) and the three very
low surface brightness galaxy candidates in Virgo from Mi-
hos et al. (2015). For comparison, we also show Virgo clus-
ter early- and late-type galaxies (compilation of Lisker et al.
2013; based on the Virgo Cluster Catalogue (VCC), Binggeli
et al. 1985), Virgo cluster dSphs (Lieder et al. 2012), as well
as dSphs from the Local Group (McConnachie 2012).
Our sample spans a parameter range of 24.8 ≤ µV 50 ≤
27.1 mag arcsec−2, −11.8 ≥ MV ≥ −15.5 mag and 0.7 ≤ r50 ≤
4.1 kpc. The surface brightness range of our sample is com-
parable to the LSB galaxy sample from van Dokkum et al.
(2015a) and approaches the surface brightness of the two
brighter Virgo LSB candidates from Mihos et al. (2015).
With regard to magnitudes and sizes our sample includes
smaller and fainter LSB candidates than the sample from
van Dokkum et al. (2015a), which is likely due to their
9 Only two galaxies are contained in the central bin with r <
100 kpc.
MNRAS 000, 1–16 (2017)
10. 10 Wittmann et al.
Figure 4. Spatial distribution of LSB galaxy candidates in the Perseus cluster core (central panel) and candidates with signs of possible
tidal disruption (side panels). Red dots indicate our sample of LSB candidates. The dashed squares on the mosaic indicate the size of
the cutout regions shown as side panels. These images were smoothed except the image in the top left side panel, which shows a cutout
from the original data. The red dots with black circles mark the positions of candidates 26, 31 and 44 shown in the side panels on the
right-hand side. The two galaxies with the tidal structures in the left side panels are not part of our LSB galaxy sample. The image
height and width of the mosaic is 0.58 deg ( ˆ= 0.71 Mpc). North is up and east is to the left.
0 5 10 15 20 25 30 35
clustercentric distance (arcmin)
0.02
0.04
0.06
0.08
0.10
0.12
ΣN(arcmin−2)
0 100 200 300 400 500 600 700
clustercentric distance (kpc)
Figure 5. Radial projected number density distribution as a
function of clustercentric distance of our sample of LSB galaxy
candidates in the Perseus cluster core. The radial bins have a
width of 100 kpc. Shown are the statistical error bars.
resolution limit. At faint magnitudes, our samples overlaps
with the parameter range of cluster and Local Group dSphs.
We note that the apparent relation between magnitude and
size of our sample is created artificially. The bright surface
brightness limit arises due to our definition of including only
sources fainter than µV 50 = 24.8 mag arcsec−2 in our sam-
ple. The faint limit is due to our detection limit.
At brighter magnitudes MV ≤ −14 mag, the LSB can-
didates of our sample are systematically smaller at a given
magnitude than the LSB candidates identified in the Coma
cluster, with all but one LSB candidate having r50 < 3 kpc.
However, van Dokkum et al. (2015a) cover a much larger
area of the Coma cluster, while we only surveyed the core
region of Perseus.10 Our total observed area corresponds to
0.41 Mpc2. This translates to a circular equivalent area with
a radius of R = 0.15 Rvir,Perseus, when assuming a virial radius
for Perseus of Rvir,Perseus = 2.44 Mpc (Mathews et al. 2006).11
When selecting all LSB candidates from the van
Dokkum et al. (2015a) sample that are located in the core
of Coma, within a circular area with clustercentric distances
smaller than R = 0.15 Rvir,Coma, where Rvir,Coma = 2.8 Mpc
(Lokas & Mamon 2003), seven LSB candidates remain.
These are marked with black squares in Fig. 6. One can see
that also only two of them reach sizes of r50 > 3 kpc. Since
the sample of van Dokkum et al. (2015a) has a brighter mag-
nitude and larger size limit than our study, we restrict the
comparison to objects with MV ≤ −14 mag and r50 ≥ 2 kpc,
which should well have been detected by van Dokkum et al.
(2015a). Five LSB candidates in the Coma cluster core are
in this parameter range, whereas in Perseus we find seven.
A similar result is obtained when comparing to the indepen-
dent sample of Coma cluster LSB galaxy candidates from
10 According to tests with the inserted model galaxies (see Sec-
tion 3) sources in the surface brightness range of the LSB galaxy
sample from van Dokkum et al. (2015a) can easily be detected in
our data.
11 We note that our field is not centred directly on the cluster
centre, but extends to the west of it.
MNRAS 000, 1–16 (2017)
11. Low surface brightness galaxies in Perseus 11
−22−20−18−16−14−12−10
100
101
102
r50(kpc)
Virgo early and late
type galaxies
Virgo dSphs
LG dSphs
Virgo LSBs
Perseus LSBs
Coma LSBs
Coma (core) LSBs
−12 −14 −16
MV (mag)
−22−20−18−16−14−12−10
MV (mag)
18
20
22
24
26
28
⟨μV⟩50(magarcsec-2)
−12 −14 −16
MV (mag)
Figure 6. Structural parameters of faint LSB galaxy candidates in the Perseus cluster core (left-hand panels). We compare our sample
to LSB galaxy candidates in the Virgo cluster (Mihos et al. 2015), and to LSB galaxies and candidates in the Coma cluster (van
Dokkum et al. 2015a). We mark those LSB objects in Coma that are located in the cluster core within a circular area with a radius of
R = 0.15 Rvir,Coma. This corresponds to an area of similar extent as our observed area of the Perseus cluster core (see Section 5.2). For
comparison, we also show early- and late-type galaxies from the Virgo cluster (compilation of Lisker et al. 2013; based on the VCC),
Virgo dSphs (Lieder et al. 2012) and dSphs from the Local Group (McConnachie 2012). We transformed the magnitudes of the LSB
candidates from van Dokkum et al. (2015a) and the galaxies from Lisker et al. (2013) with the transformation equations from Jester
et al. (2005). For the former, we assumed g − r = 0.6, for the latter we used the measured g − r colours. The two panels on the right-hand
side show our typical uncertainties that occur for LSB galaxy models (n = 1, ellipticity = 0.1) in the parameter range of our sample (see
Section 5.3). We created eight model types with different parameters. Each model type was inserted 10 times at different positions into
one copy of our mosaic. The black arrows indicate our systematic parameter uncertainties. The arrow tips point to the true parameters
of the models, the endpoints represent the average measured parameter values of the 10 inserted models of each type. On average the
measured MV values are by 0.4 mag too faint, the measured r50 values are underestimated by 0.5 kpc and the measured µV 50 values
are by 0.1 mag arcsec−2 too bright. The error bars represent our statistical uncertainties, and were calculated as standard deviation of
the measured values of each model type.
Yagi et al. (2016). When selecting LSB candidates of the
Coma core region in the same surface brightness range as
our sample and with MV ≤ −14 mag and r50 ≥ 2 kpc, we find
10 LSB candidates in this parameter range, where three LSB
candidates have r50 ≥ 3 kpc. While it seems that the Virgo
cluster galaxies shown in Fig. 6 are also rare in this parame-
ter range, we note that the catalogue we used is not complete
at magnitudes fainter than Mr = −15.2 mag.
Thus, in summary, we find that first, the core regions of
the Perseus and the Coma cluster harbour a similar number
of faint LSB galaxy candidates in the same parameter range
of MV ≤ −14 mag and r50 ≥ 2 kpc, and secondly, that large
MNRAS 000, 1–16 (2017)
12. 12 Wittmann et al.
Figure 7. Objects from our sample that could be either LSB
galaxies with possible tidal streams or cirrus emission. The top
panels show the objects in our smoothed data, marked with red
circles. The four lower panels show the corresponding regions in
the WISE 12µm intensity maps that trace Galactic cirrus. The
original WISE intensity maps with 6 arcsec resolution are dis-
played in the middle panels, the reprocessed WISE intensity maps
with 15 arcsec resolution that were cleaned from point sources are
shown in the bottom panels. The height and width of the cutout
regions is 2 arcmin ( ˆ= 41 kpc) in the left-hand panels and 4 arcmin
( ˆ= 81 kpc) in the right-hand panels, respectively. The black bar
in the images in the top panels denotes a length of 10 kpc. We
see no obvious correspondence between the structures observed in
our data and the 12µm emission. We therefore cannot draw any
firm conclusions on the nature of these structures.
LSB candidates with r50 ≥ 3 kpc seem to be very rare in
both cluster cores.
5.3 Uncertainties
In Fig. 6, we try to include realistic photometric uncer-
tainties for our sample. Our major source of uncertainty
in the measured total fluxes, which translate to uncertain-
ties in half-light radii and surface brightnesses, lies in the
adopted background level (see Section 4). To test how large
the resulting uncertainties are, we probed this using in-
serted LSB galaxy models that were generated similarly
to those described in Section 3. We created eight model
types that span the parameter range of our sample. Four
model types have µV 50 = 25.5 mag arcsec−2, the other four
have µV 50 = 26.5 mag arcsec−2, with varying magnitudes
MV = −12.5 to −15.5 mag and sizes 0.8 ≤ r50 ≤ 4.9 kpc. The
models have one component S´ersic profiles with n = 1, are
nearly round (ellipticity = 0.1) and were convolved to our
average seeing FWHM. We inserted 10 models of each type
into one copy of our mosaic, respectively. We then measured
MV , r50 and µV 50 similarly to our sample of real LSB can-
didates. We calculated the average offset between true and
measured parameters for each model type, as well as the
scatter of the measured parameters.
We indicate the average parameter offsets with arrows
in the right-hand panels of Fig. 6. The arrow tips point to
the true values, with MV being systematically estimated as
too faint by on average 0.4 mag, and r50 being underesti-
mated by on average 0.5 kpc. We largely preserved the true
surface brightness, which results from our approach of con-
sidering the uncontaminated part of the flux profile only (see
Section 4). The offsets in µV 50 are small, and do not ex-
ceed 0.1 mag arcsec−2. In general the parameter offsets are
more severe for model types with the largest size and faintest
surface brightness, and negligible for model types with the
smallest size and brightest surface brightness. The error bars
in Fig. 6 give the standard deviation of the measured MV , r50
and µV 50 values for each model type, with average stan-
dard deviations of ∆MV = ±0.3 mag, ∆r50 = ±0.3 kpc and
µV 50 = ±0.1 mag arcsec−2.
We also tested the implications of our estimated un-
certainties on our results from Section 5.2, and applied
the average systematic offsets in MV , r50 and µV 50 be-
tween the models and the measured parameters of our LSB
galaxy sample. In this case the number of LSB candidates
in the considered parameter range of MV ≤ −14 mag and
r50 ≥ 2 kpc would increase to 25 candidates in the Perseus
cluster core, but still only two LSB candidates would have
sizes larger than r50 ≥ 3 kpc. Thus, while the number of
LSB candidates would now be significantly higher in Perseus
compared to the number of LSB candidates in the same pa-
rameter range in the Coma cluster core, the conclusion of
only finding very few large LSB galaxy candidates in the
cluster core would remain unchanged.
Since the core regions of massive clusters are char-
acterized by a particularly high density of galaxies, one
possible concern is that this may have influenced our
ability of detecting large LSB galaxy candidates with
r50 ≥ 3 kpc. Our tests with the inserted LSB galaxy models
indicate, however, that we are in principle able to detect
objects with r50 > 3 kpc in the surface brightness range
µV 50 < 27 mag arcsec−2 in our data, if these were present
(see Section 3). Nevertheless we might have missed objects
in close vicinity to bright cluster galaxies or foreground
stars, although we modelled and subtracted the light profile
of the latter in most cases. The apparent absence of LSB
candidates in regions around bright sources in Fig. 4 might
therefore not be a real effect.
Due to the location of the Perseus cluster at low Galac-
tic latitude (l = 13◦) we cannot exclude the presence of
diffuse emission from Galactic cirrus in our data. Cirrus is
often visible in deep wide-field imaging data, and the result-
ing structures can be very similar in appearance to stellar
tidal streams (cf. Miville-Deschˆenes et al. 2016). We there-
fore compared our candidates with possible streams to the
MNRAS 000, 1–16 (2017)
13. Low surface brightness galaxies in Perseus 13
WISE12 12µm data that trace Galactic cirrus, in order to
search for possible counterparts in the 12µm emission. Fig. 7
shows our data in comparison to both the original WISE
data with 6 arcsec resolution, as well as to the reprocessed
data from Meisner & Finkbeiner (2014) with 15 arcsec reso-
lution that were cleaned from point sources. We clearly see
diffuse emission in the 12µm data at the position of Perseus.
However, we are not able to identify obvious structures in the
WISE maps that would match to the candidates with pos-
sible streams we observe in our data, due to the insufficient
resolution of the latter. Therefore, we neither can confirm
nor exclude that the nature of these structures may be cir-
rus emission rather than LSB galaxy candidates with tidal
streams.
6 DISCUSSION
We detected a large number of 89 faint LSB galaxy candi-
dates with µV 50 ≥ 24.8 mag arcsec−2 in the Perseus cluster
core. It is interesting to note that all but one candidate have
r50 < 3 kpc. We thus speculate that LSB galaxies with larger
sizes cannot survive the strong tidal forces in the core region
and possibly have lost already a considerable amount of their
dark matter content. This observation is consistent with the
study of van der Burg et al. (2016) who found a decreasing
number density of faint LSB galaxy candidates in the cores
of galaxy clusters. Also, the numerical simulations of Yozin
& Bekki (2015) predicted the disruption of LSB galaxies or-
biting close to the cluster centre.
The effect of tides on LSB galaxies in galaxy clus-
ters is possibly also reflected in the radial number density
distribution we observe for our sample. The nearly con-
stant projected number density for clustercentric distances
r ≥ 100 kpc implies that the three-dimensional distribution
should actually increase with distance from the cluster cen-
tre. This may be a further argument that LSB galaxies are
depleted in the cluster core region due to tidal disruption.
Very close to the cluster centre, for clustercentric distances
r < 100 kpc, the number density drops, with only two LSB
candidates from our sample being located in this region.
Here tidal effects from the central cluster galaxy NGC 1275
may become apparent (cf. Mathews et al. 2006, fig. 1).
For example, the slightly more compact peculiar galaxy
SA 0426-002 (MB = −16.3 mag, r50 = 2.1 kpc), being located
only ∼ 30 kpc from the cluster centre, shows signs of being
tidally disturbed (see Fig. 4, top left panel). Also, in the
Fornax cluster core a drop in the number density profile of
faint LSB candidates is seen within 180 kpc of the cluster
centre (Venhola et al. 2017).
We can use the observed limit in r50 as a rough con-
straint on the dark matter content of the LSB candidates in
the cluster centre (cf. Penny et al. 2009). The tidal radius
Rtidal is given by
Rtidal = Rperi
Mobj
Mcl(Rperi) (3 + e)
1/3
, (1)
with the pericentric distance Rperi, the total object mass
12 Wide-field Infrared Survey Explorer (Wright et al. 2010)
Mobj, the cluster mass Mcl(Rperi) within Rperi and the ec-
centricity of the orbit e (King 1962). We find about 50 per
cent of our sample (44 objects) at projected clustercentric
distances below 330 kpc. Assuming that this is representa-
tive of the orbital pericentre for at least a fraction of the
population,13 we estimate Rtidal for a typical LSB candidate
of our sample with MV = −14 mag and Rperi = 330 kpc,
assuming an eccentric orbit with e = 0.5. We adopt the
cluster mass profile from Mathews et al. (2006), where
Mcl(330 kpc) = 1.3 × 1014 M .
Assuming a galaxy without dark matter, and adopting
a mass-to-light ratio of M/LV = 2 for an old stellar popu-
lation with subsolar metallicity (Bruzual & Charlot 2003),
the mass of an object with MV = −14 mag would be Mobj =
7 × 107 M accordingly, resulting in a tidal radius of 1.8 kpc.
This compares to a range of observed r50 1.0 − 2.5 kpc for
LSB candidates from our sample with MV −14 mag. We
note that we can generally probe our objects out to more
than one half-light radius in our data, thus the tidal radius
would be within the observed stellar extent. However, since
most objects from our sample do not show obvious signs of
current disruption, we suspect that they may contain addi-
tional mass in order to prevent tidal disruption.
If we assume a higher mass-to-light ratio of M/LV = 10,
the tidal radius of the same object would increase to 2.9 kpc.
For M/LV = 100 the tidal radius would be Rtidal = 6.2 kpc,
and for M/LV = 1000 we derive Rtidal = 13.3 kpc. For M/LV
close to 1000 the tidal radius is significantly larger than the
observed range of half-light radii. If such a high mass-to-light
ratio would be reached within the tidal radius, we might ex-
pect to find a higher number of galaxies with r50 3 kpc in
the cluster core. However, for M/LV 100, the tidal radius
would be on the order of 1–2 r50, which is also consistent
with the mass-to-light ratios derived from dynamical mea-
surements of similar galaxies. For example, van Dokkum
et al. (2016) found a mass-to-light ratio of ∼ 50 within
one half-light radius for one LSB galaxy in the Coma clus-
ter (MV = −16.1 mag, r50 = 4.3 kpc),14 and Beasley et al.
(2016) derived a mass-to-light ratio of ∼ 100 within one half-
light radius for one LSB galaxy in Virgo (Mg = −13.3 mag,
r50 = 2.8 kpc).15 We note that based on similar analytical ar-
guments as described above van Dokkum et al. (2015a) also
estimated a dark matter fraction of 100 per cent within
an assumed tidal radius of 6 kpc for a sample of faint LSB
candidates within the core region of the Coma cluster.
While the above approach gives an estimate of the ra-
dius beyond which material is likely going to be stripped,
another approach to estimate the effect of tides on galax-
ies in clusters is to compare the density of the tidal field to
the density of the orbiting galaxy (cf. Gnedin 2003). The
density of the tidal field ρtidal is given by Poisson’s equa-
tion, ρtidal = Ftidal/(4πG), where Ftidal is the trace of the tidal
tensor. We consider the extended mass distribution of the
13 While on the one hand, most objects are likely to be situated
somewhat further away from the centre than the projected value
suggests, on the other hand, it is also likely that their orbital
pericentre is located further inwards from their current location.
14 Based on stellar dynamics of the galaxy.
15 Based on GC system dynamics of the galaxy.
MNRAS 000, 1–16 (2017)
14. 14 Wittmann et al.
cluster16 and approximate the strength of the tidal force at a
given clustercentric distance r0 as Ftidal = |dg(r)/dr|r0 , where
g(r) is the gravitational acceleration exerted by the mass
of the cluster. For g(r) we adopt the gravitational accelera-
tion due to the Perseus cluster potential given by Mathews
et al. (2006), where we only consider the contribution of
the NFW-profile, which is the dominant component at clus-
tercentric distances r 10 kpc. We approximate the average
density of the orbiting galaxy, assuming spherical symmetry,
as ρgal = Mgal(R)/(4πR3/3), where Mgal(R) is the total mass
of the galaxy within a radius R. Requiring that the density
of the galaxy is larger than the tidal density to prevent its
disruption, the limiting radius Rlim is given as
Rlim ≥
3
3GMgal(R)
|dg(r)/dr|r0
(2)
Considering again a typical galaxy from our sample, with
MV = −14 mag at a clustercentric distance r0 = 330 kpc,
we find Rlim = 0.8 kpc for M/LV = 2, Rlim = 1.3 kpc for
M/LV = 10, Rlim = 2.8 kpc for M/LV = 100 and Rlim =
6.1 kpc for M/LV = 1000. Thus, in comparison to the tidal
radius derived with the first approach, the limiting radius
obtained with the second approach is a factor of two smaller.
If we assume that M/LV = 100 would be characteristic for a
considerable fraction of our sample, then the limiting radius
would be on the order of only 1 r50.
Does this imply that a few of the largest LSB candidates
in the Perseus cluster core should be in process of tidal dis-
ruption right now? – We do identify three LSB candidates
in Perseus that show possible signs of disruption (see pan-
els on the right-hand side in Fig. 4). Candidate 44 appears
to be embedded in stream like filaments. It is, however, un-
clear whether we see here still a bound galaxy or rather a
remnant core of a stream. Candidates 26 and 31 seem to
be connected via an arc-like tidal stream. This could point
to a low-velocity interaction between those two candidates,
since such interactions produce the most severe mass-loss.
The convex shape of the stream with respect to the cluster
centre might suggest that these two objects are not in or-
bit around the cluster centre, but instead still bound to a
possibly recently accreted subgroup of galaxies. The associa-
tion with a subgroup could be supported by the observation
that these three candidates, together with the candidate of
brighter surface brightness with tidal tails (see Fig. 4, lower
left panel), are located closely together in a region south–
west of the cluster centre, within a clustercentric distance
range of 300–400 kpc. It is also interesting to note that Mer-
ritt et al. (2016) found a generally more complex and dis-
torted morphology for LSB candidates in galaxy groups than
in galaxy clusters, indicating that the group environment
may play an important role in shaping galaxies of low stel-
lar density.
The comparison to the LSB galaxy samples in Coma
(van Dokkum et al. 2015a; Yagi et al. 2016) showed that
both cluster cores hold a similar number of faint LSB can-
didates with r50 ≥ 2 kpc and MV ≤ −14 mag. Based on the
16 Unlike in the first approach, where a point-mass approximation
was used.
1.5 times lower cluster mass of Perseus17, we would expect
a somewhat lower number of all galaxy types in Perseus.
However, with regard to the density in the cluster core, both
clusters reach a comparable galaxy surface number density
within 0.5 Mpc (Weinmann et al. 2011), thus causing com-
parable disruptive forces in both cluster cores. Therefore,
according to the cluster mass and density, we would expect
a similar or even lower number of LSB galaxies of such large
size in Perseus, which is in agreement with our observations.
One important question to investigate would be whether
there exists a possible evolutionary link between LSB galax-
ies that are red and quiescent and those that are blue and
star-forming. The cosmological simulations of Di Cintio et al.
(2017) suggest that faint LSB galaxies with large sizes may
form as initially gas-rich star-forming systems in low-density
environments. In this context, the quenching of star for-
mation should be related to external processes, like, e.g.,
ram pressure stripping. Rom´an & Trujillo (2017) examined
a sample of faint LSB candidates in group environments.
Since they found the red LSB candidates closer to the re-
spective group’s centre than the blue systems this could im-
ply that the group environment was efficient in removing
the gas that fuels star formation. This is also seen among
the dwarf galaxies of the Local Group, which show a pro-
nounced morphology – gas content – distance relation (see
Grebel et al. 2003). However, a few quiescent and gas-poor
LSB galaxies of dwarf luminosity are also observed in isola-
tion (e.g. Papastergis et al. 2017), which would not fit into
this scenario. An essential aspect would be to understand
whether the physical processes governing the formation and
evolution of LSB galaxies are controlled by stellar density
or by stellar mass. The latter could possibly explain the ob-
served wide variety of LSB galaxy properties from low-mass
dSphs to massive LSB disc galaxies.
7 SUMMARY AND CONCLUSIONS
We obtained deep V-band imaging data under good see-
ing conditions of the central regions of Perseus with PFIP
at the WHT that we used to search for faint LSB galax-
ies in the surface brightness range of the so-called ‘ultra-
diffuse galaxies’. We detected an abundant population of 89
faint LSB galaxy candidates for which we performed pho-
tometry and derived basic structural parameters. Our sam-
ple is characterized by mean effective surface brightnesses
24.8 ≤ µV 50 ≤ 27.1 mag arcsec−2, total magnitudes −11.8 ≥
MV ≥ −15.5 mag and half-light radii 0.7 ≤ r50 ≤ 4.1 kpc. A
comparison to overlapping HST/ACS imaging data indicates
that the sample is relatively uncontaminated by background
objects.
We find good evidence for tidal disruption leading to a
deficiency of LSB galaxy candidates in the central regions of
the cluster. This is indicated by a constant observed number
density beyond clustercentric distances of 100 kpc and the
lack of very large LSB candidates with r50 ≥ 3 kpc except for
one object. However, only a few candidates show structural
17 Assuming Mvir,Coma = 1.3×1015 M (Lokas & Mamon 2003) and
Mvir,Perseus = 8.5 × 1014 M (Mathews et al. 2006).
MNRAS 000, 1–16 (2017)
15. Low surface brightness galaxies in Perseus 15
evidence of ongoing tidal disruption. If LSB systems are to
remain gravitationally bound in the cluster core, the density
limits set by the Perseus cluster tidal field require that they
have high M/L values of about 100, assuming a standard
model for gravity.
In comparison to the Coma cluster – with its compa-
rable central density to Perseus – we find that our sample
statistically resembles the LSB galaxy population in the cen-
tral regions of Coma. Given the same dearth of large objects
with r50 ≥ 3 kpc in both cluster cores we conclude that these
cannot survive the strong tides in the centres of massive
clusters.
ACKNOWLEDGEMENTS
The William Herschel Telescope is operated on the island of
La Palma by the Isaac Newton Group of Telescopes in the
Spanish Observatorio del Roque de los Muchachos of the In-
stituto de Astrof´ısica de Canarias (programme 2012B/045).
We thank Simone Weinmann and Stefan Lieder for useful
comments when preparing the WHT observing proposal.
CW is a member of the International Max Planck Research
School for Astronomy and Cosmic Physics at the University
of Heidelberg (IMPRS-HD). RK gratefully acknowledges fi-
nancial support from the National Science Foundation under
grant no. AST-1664362. This research has made use of the
NASA/ IPAC Infrared Science Archive, which is operated by
the Jet Propulsion Laboratory, California Institute of Tech-
nology, under contract with the National Aeronautics and
Space Administration.
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