3,942 research outputs found
On the lack of stellar bars in Coma dwarf galaxies
We present a study of the bar fraction in the Coma cluster galaxies based on
a sample of ~190 galaxies selected from the SDSS-DR6 and observed with the
Hubble Space Telescope (HST) Advanced Camera for Survey (ACS). The
unprecedented resolution of the HST-ACS images allows us to explore the
presence of bars, detected by visual classification, throughout a luminosity
range of 9 mag (-23 < M_r < -14), permitting us to study the poor known region
of dwarf galaxies. We find that bars are hosted by galaxies in a tight range of
both luminosities (-22 < M_r < -17) and masses (10^9 < M*/Msun < 10^11). In
addition, we find that the bar fraction does not vary significantly when going
from the center to the cluster outskirts, implying that cluster environment
plays a second-order role in bar formation/evolution. The shape of the bar
fraction distribution with respect to both luminosity and mass is well matched
by the luminosity distribution of disk galaxies in Coma, indicating that bars
are good tracers of cold stellar disks.Comment: 2 pages, 1 figure, to appear in the proceedings of the conference "A
Universe of Dwarf Galaxies" (Lyon, June 14-18, 2010
Deep spectroscopic luminosity function of Abell 85: no evidence for a steep upturn of the faint-end slope
We present a new deep determination of the spectroscopic LF within the virial
radius of the nearby and massive Abell\,85 (A85) cluster down to the dwarf
regime (M* + 6) using VLT/VIMOS spectra for galaxies with m mag and mag arcsec. The
resulting LF from 438 cluster members is best modelled by a double Schechter
function due to the presence of a statistically significant upturn at the
faint-end. The amplitude of this upturn (),
however, is much smaller than that of the SDSS composite photometric cluster LF
by Popesso et al. 2006, -2. The faint-end slope of the LF in
A85 is consistent, within the uncertainties, with that of the field. The red
galaxy population dominates the LF at low luminosities, and is the main
responsible for the upturn. The fact that the slopes of the spectroscopic LFs
in the field and in a cluster as massive as A85 are similar suggests that the
cluster environment does not play a major role in determining the abundance of
low-mass galaxies.Comment: 6 pages, 4 figures, accepted at MNRAS lette
The sensitivity of harassment to orbit: Mass loss from early-type dwarfs in galaxy clusters
We conduct a comprehensive numerical study of the orbital dependence of harassment on early-type dwarfs consisting of 168 different orbits within a realistic, Virgo-like cluster, varying in eccentricity and pericentre distance. We find harassment is only effective at stripping stars or truncating their stellar discs for orbits that enter deep into the cluster core. Comparing to the orbital distribution in cosmological simulations, we find that the majority of the orbits (more than three quarters) result in no stellar mass loss. We also study the effects on the radial profiles of the globular cluster systems of early-type dwarfs. We find these are significantly altered only if harassment is very strong. This suggests that perhaps most early-type dwarfs in clusters such as Virgo have not suffered any tidal stripping of stars or globular clusters due to harassment, as these components are safely embedded deep within their dark matter halo. We demonstrate that this result is actually consistent with an earlier study of harassment of dwarf galaxies, despite the apparent contradiction. Those few dwarf models that do suffer stellar stripping are found out to the virial radius of the cluster at redshift = 0, which mixes them in with less strongly harassed galaxies. However when placed on phase-space diagrams, strongly harassed galaxies are found offset to lower velocities compared to weakly harassed galaxies. This remains true in a cosmological simulation, even when haloes have a wide range of masses and concentrations. Thus phase-space diagrams may be a useful tool for determining the relative likelihood that galaxies have been strongly or weakly harassed
Search for Blue Compact Dwarf Galaxies During Quiescence
Blue Compact Dwarf (BCD) galaxies are metal poor systems going through a
major starburst that cannot last for long. We have identified galaxies which
may be BCDs during quiescence (QBCD), i.e., before the characteristic starburst
sets in or when it has faded away. These QBCD galaxies are assumed to be like
the BCD host galaxies. The SDSS/DR6 database provides ~21500 QBCD candidates.
We also select from SDSS/DR6 a complete sample of BCD galaxies to serve as
reference. The properties of these two galaxy sets have been computed and
compared. The QBCD candidates are thirty times more abundant than the BCDs,
with their luminosity functions being very similar except for the scaling
factor, and the expected luminosity dimming associated with the end of the
starburst. QBCDs are redder than BCDs, and they have larger HII region based
oxygen abundance. QBCDs also have lower surface brightness. The BCD candidates
turn out to be the QBCD candidates with the largest specific star formation
rate (actually, with the largest H_alpha equivalent width). One out of each
three dwarf galaxies in the local universe may be a QBCD. The properties of the
selected BCDs and QBCDs are consistent with a single sequence in galactic
evolution, with the quiescent phase lasting thirty times longer than the
starburst phase. The resulting time-averaged star formation rate is low enough
to allow this cadence of BCD -- QBCD phases during the Hubble time.Comment: Accepted for publication in ApJ. 17 pages. 13 Fig
Fossil group origins - VI. Global X-ray scaling relations of fossil galaxy clusters
We present the first pointed X-ray observations of 10 candidate fossil galaxy
groups and clusters. With these Suzaku observations, we determine global
temperatures and bolometric X-ray luminosities of the intracluster medium (ICM)
out to for six systems in our sample. The remaining four systems show
signs of significant contamination from non-ICM sources. For the six objects
with successfully determined properties, we measure global
temperatures in the range ,
bolometric X-ray luminosities of , and estimate masses,
as derived from , of .
Fossil cluster scaling relations are constructed for a sample that combines our
Suzaku observed fossils with fossils in the literature. Using measurements of
global X-ray luminosity, temperature, optical luminosity, and velocity
dispersion, scaling relations for the fossil sample are then compared with a
control sample of non-fossil systems. We find the fits of our fossil cluster
scaling relations are consistent with the relations for normal groups and
clusters, indicating fossil clusters have global ICM X-ray properties similar
to those of comparable mass non-fossil systems.Comment: 17 pages, 7 figures, 8 tables. Accepted for publication in MNRA
Properties of the Dwarf Galaxy Population in Galaxy Clusters
We present the observational properties of the dwarf galaxy population (Mr >
M*+1) corresponding to one of the largest samples of spectroscopically
confirmed galaxy cluster members reported in the literature. We have observed
that red dwarf galaxies (u-r > 2.22) share the same cluster environment as the
brightest cluster members (Mr < -21), but are not in dynamical equilibrium. We
computed the dwarf-to-giant ratio (DGR) using a spectroscopically selected
sample. The DGR was found to vary with clustercentric distance, essentially due
to the blue dwarf population (u-r < 2.22). The u-r color of red dwarf galaxies
was independent of their environment and similar to the color of red isolated
dwarfs. Blue dwarf galaxies located outside r200 show similar u-r colors to
those of the field population, while strong reddening was observed toward the
cluster center. We also present evidence that the fraction of red to blue dwarf
galaxies in clusters is larger in the innermost cluster regions. We conclude
that the present red dwarf population observed in the central regions of nearby
galaxy clusters could be related to the blue dwarf population observed in
clusters at high redshift.Comment: 5 pages, 3 color figures, accepted for publication in the ApJ Letter
The Luminosity Function of Galaxies in the Hercules Cluster
We have imaged 1 deg in the V-band in the direction of the
Hercules Cluster (Abell 2151). The data are used to compute for the first time
the luminosity function (LF) of galaxies in the cluster down to the dwarf
regime (M -13.85). The global LF is well described by a
Schechter function (\cite{schechter76}) with best-fit parameters =
-1.30 0.06 and M = -21.25 0.25. The radial dependence of
the LF has also been studied, finding that it turns out to be almost constant
within the errors even further away than the virial radius. Given the presence
of significant substructure within the cluster, we have analized the LFs in
different regions. While two of the subclusters present LFs consistent with
each other and with the global one, the southernmost one exhibits a somewhat
steeper faint-end slope.Comment: 3 pages, to appear in Proc. of IAU Colloq. 195: "Outskirts of Galaxy
Clusters: Intense Life in the Suburbs
The Sensitivity of Harassment to Orbit: Mass Loss from Early-Type Dwarfs in Galaxy Clusters
We conduct a comprehensive numerical study of the orbital dependence of
harassment on early-type dwarfs consisting of 168 different orbits within a
realistic, Virgo-like cluster, varying in eccentricity and pericentre distance.
We find harassment is only effective at stripping stars or truncating their
stellar disks for orbits that enter deep into the cluster core. Comparing to
the orbital distribution in cosmological simulations, we find that the majority
of the orbits (more than three quarters) result in no stellar mass loss. We
also study the effects on the radial profiles of the globular cluster systems
of early-type dwarfs. We find these are significantly altered only if
harassment is very strong. This suggests that perhaps most early-type dwarfs in
clusters such as Virgo have not suffered any tidal stripping of stars or
globular clusters due to harassment, as these components are safely embedded
deep within their dark matter halo. We demonstrate that this result is actually
consistent with an earlier study of harassment of dwarf galaxies, despite the
apparent contradiction. Those few dwarf models that do suffer stellar stripping
are found out to the virial radius of the cluster at redshift=0, which mixes
them in with less strongly harassed galaxies. However when placed on
phase-space diagrams, strongly harassed galaxies are found offset to lower
velocities compared to weakly harassed galaxies. This remains true in a
cosmological simulation, even when halos have a wide range of masses and
concentrations. Thus phase-space diagrams may be a useful tool for determining
the relative likelihood that galaxies have been strongly or weakly harassed.Comment: 17 pages, 13 figures, Accepted to MNRAS 8th September 201
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