37 research outputs found
Does the stellar disc flattening depend on the galaxy type?
We analyze the dependence of the stellar disc flatness on the galaxy
morphological type using 2D decomposition of galaxies from the reliable
subsample of the Edge-on Galaxies in SDSS (EGIS) catalogue. Combining these
data with the retrieved models of the edge-on galaxies from the Two Micron All
Sky Survey (2MASS) and the Spitzer Survey of Stellar Structure in Galaxies
(SG) catalogue, we make the following conclusions:
(1) The disc relative thickness in the near- and mid-infrared
passbands correlates weakly with morphological type and does not correlate with
the bulge-to-total luminosity ratio in all studied bands.
(2) Applying an 1D photometric profile analysis overestimates the disc
thickness in galaxies with large bulges making an illusion of the relationship
between the disc flattening and the ratio .
(3) In our sample the early-type disc galaxies (S0/a) have both flat and
"puffed" discs. The early spirals and intermediate-type galaxies have a large
scatter of the disc flatness, which can be caused by the presence of a bar:
barred galaxies have thicker stellar discs, on average. On the other hand, the
late-type spirals are mostly thin galaxies, whereas irregular galaxies have
puffed stellar discs.Comment: 17 pages, 17 figures, accepted for publication in MNRA
Initial Mass Function Effects on the Colour Evolution of Disk Galaxies
Aims. In this work, we want to find out if the IMF can be determined from colour images, integrated colours, or mass-to-light ratios, especially at high redshift, where galaxies cannot be resolved into individual stars, which would enable us to investigate dependencies of the IMF on cosmological epoch.
Methods. We use chemo-dynamical models to investigate the influence of the Initial Mass Function (IMF) on the evolution of a Milky Way-type disk galaxy, in particular of its colours.
Results. We find that the effect of the IMF on the internal gas absorption is larger than its effect on the light from the stellar content. However, the two effects work in the opposite sense: An IMF with more high mass stars leads to brighter and bluer star-light, but also to more interstellar dust and thus to more absorption, causing a kind of âIMF degeneracyâ. The most likely wavelength region in which to detect IMF effects is the infrared (i.e., JHK). We also provide photometric absorption and inclination corrections in the SDSS ugriz and the HST WFPC2 and NICMOS systems
The Catalog of Edge-on Disk Galaxies from SDSS. Part I: the catalog and the Structural Parameters of Stellar Disks
We present a catalog of true edge-on disk galaxies automatically selected
from the Seventh Data Release (DR7) of the Sloan Digital Sky Survey. A visual
inspection of the , and images of about 15000 galaxies allowed us to
split the initial sample of edge-on galaxy candidates into 4768 (31.8% of the
initial sample) genuine edge-on galaxies, 8350 (55.7%) non-edge-ons, and 1865
(12.5%) edge-on galaxies not suitable for simple automatic analysis because
these objects show signs of interaction, warps, or nearby bright stars project
on it. We added more candidate galaxies from RFGC, EFIGI, RC3, and Galaxy Zoo
catalogs found in the SDSS footprints. Our final sample consists of 5747
genuine edge-on galaxies. We estimate the structural parameters of the stellar
disks (the stellar disk thickness, radial scale length, and central surface
brightness) in the galaxies by analyzing photometric profiles in each of the g,
r, and i images. We also perform simplified 3-D modeling of the light
distribution in the stellar disks of edge-on galaxies from our sample. Our
large sample is intended to be used for studying scaling relations in the
stellar disks and bulges and for estimating parameters of the thick disks in
different types of galaxies via the image stacking. In this paper we present
the sample selection procedure and general description of the sample.Comment: Accepted for publication in Ap
The fraction of early-type galaxies in low redshift groups and clusters of galaxies
We examine the fraction of early-type (and spiral) galaxies found in groups
and clusters of galaxies as a function of dark matter halo mass. We use
morphological classifications from the Galaxy Zoo project matched to halo
masses from both the C4 cluster catalogue and the Yang et al (2007) group
catalogue. We find that the fraction of early-type (or spiral) galaxies remains
constant (changing by less than 10%) over three orders of magnitude in halo
mass (13<log MH/Msol/h<15.8). This result is insensitive to our choice of halo
mass measure, from velocity dispersions or summed optical luminosity.
Furthermore, we consider the morphology-halo mass relations in bins of galaxy
stellar mass M*, and find that while the trend of constant fraction remains
unchanged, the early-type fraction amongst the most massive galaxies (11<log
M*/Msol/h <12) is a factor of three greater than lower mass galaxies
(10<logM*/Msol/h<10.7). We compare our observational results with those of
simulations presented in De Lucia et al (2011), as well as previous
observational analyses, and semi-analytic bulge (or disc) dominated galaxies
from the Millennium Simulation. We find the simulations recover similar trends
as observed, but may over-predict the abundances of the most massive bulge
dominated (early-type) galaxies. Our results suggest that most morphological
transformation is happening on the group scale before groups merge into massive
clusters. However, we show that within each halo a morphology-density relation
remains: it is summing the total fraction to a self-similar scaled radius which
results in a flat morphology-halo mass relationship.Comment: 9 page, 5 figures, modified to match accepted version (MNRAS
Tidal streams in newly discovered M32 analogues: evidence for the stripping scenario
We present two newly-discovered compact elliptical (cE) galaxies, exhibiting
clear evidence of tidal steams, and found during a search of SDSS DR7 for cE
candidates. The structural parameters of the cEs are derived using GALFIT,
giving effective radii, Re, of 388 and 263 parsecs, and B-band mean surface
brightnesses within Re of 19.4 and 19.2 magnitudes per arcsec squared. We have
re-analysed the SDSS spectra, which indicate that they possess young to
intermediate-age stellar populations. These two cEs provide direct evidence, a
"smoking gun", for the process of tidal stripping that is believed to be the
origin of M32-type galaxies. Both are in small groups with a large spiral
fraction, suggesting that we may be seeing the formation of such cE galaxies in
dynamically young environments. The more compact of the galaxies is found in a
small group not unlike the Local Group, and thus provides an additional model
for understanding M32.Comment: 9 pages, 10 figures. Accepted to MNRA
Evolution of the Early-Type Galaxy Fraction in Clusters since z = 0.8
We study the morphological content of a large sample of high-redshift
clusters to determine its dependence on cluster mass and redshift. Quantitative
morphologies are based on bulge+disk decompositions of cluster and field
galaxies on deep VLT/FORS2 images of 18 optically-selected clusters at 0.45 < z
< 0.80 from the ESO Distant Cluster Survey (EDisCS). Morphological content is
given by the early-type galaxy fraction f_et, and early-type galaxies are
selected based on their bulge fraction and image smoothness. A set of 158 SDSS
clusters is analyzed exactly as the EDisCS sample to provide a robust local
comparison. Our main results are: (1) f_et values for the SDSS and EDisCS
clusters exhibit no clear trend as a function of sigma. (2) Mid-z EDisCS
clusters around sigma = 500 km/s have f_et ~= 0.5 whereas high-z EDisCS
clusters have f_et ~= 0.4 (~25% increase over 2 Gyrs). (3) There is a marked
difference in the morphological content of EDisCS and SDSS clusters. None of
the EDisCS clusters have f_et greater than 0.6 whereas half of the SDSS
clusters lie above this value. This difference is seen in clusters of all
velocity dispersions. (4) There is a strong correlation between morphology and
star formation in SDSS and EDisCS clusters. This correlation holds independent
of sigma and z even though the fraction of [OII] emitters decreases from z~0.8
to z~0.06 in all environments. Our results pose an interesting challenge to
structural transformation and star formation quenching processes that strongly
depend on the global cluster environment and suggest that cluster membership
may be of lesser importance than other variables in determining galaxy
properties. (ABRIDGED)Comment: 22 pages, 10 figures, accepted for publication in A&
A Spectroscopically Confirmed Excess of 24 micron Sources in a Super Galaxy Group at z=0.37: Enhanced Dusty Star Formation Relative to the Cluster and Field Environment
To trace how dust-obscured star formation varies with environment, we compare
the fraction of 24 micron sources in a super galaxy group to the field and a
rich galaxy cluster at z~0.35. We draw on multi-wavelength observations that
combine Hubble, Chandra, and Spitzer imaging with extensive optical
spectroscopy (>1800 redshifts) to isolate galaxies in each environment and thus
ensure a uniform analysis. We focus on the four galaxy groups in supergroup
1120-12 that will merge to form a galaxy cluster comparable in mass to Coma. We
find that 1) the fraction of supergroup galaxies with SFR(IR)>3 Msun/yr is four
times higher than in the cluster (32% vs. 7%); 2) the supergroup's infrared
luminosity function confirms that it has a higher density of IR members
compared to the cluster and includes bright IR sources not found in galaxy
clusters at z<0.35; and 3) there is a strong trend of decreasing IR fraction
with increasing galaxy density, i.e. an IR-density relation, not observed in
the cluster. These dramatic differences are surprising because the early-type
fraction in the supergroup is already as high as in clusters, i.e. the
timescales for morphological transformation cannot be strongly coupled to when
the star formation is completely quenched. The supergroup has a significant
fraction (~17%) of luminous, low-mass, IR members that are outside the group
cores (R>0.5 Mpc); once their star formation is quenched, most will evolve into
faint red galaxies. Our analysis indicates that the supergroup's 24 micron
population also differs from that in the field: 1) despite the supergroup
having twice the fraction of E/S0s as the field, the fraction of IR galaxies is
comparable in both environments, and 2) the supergroup's IR luminosity function
has a higher L(IR)* than that previously measured for the field.Comment: Accepted by the Astrophysical Journa
A review of elliptical and disc galaxy structure, and modern scaling laws
A century ago, in 1911 and 1913, Plummer and then Reynolds introduced their
models to describe the radial distribution of stars in `nebulae'. This article
reviews the progress since then, providing both an historical perspective and a
contemporary review of the stellar structure of bulges, discs and elliptical
galaxies. The quantification of galaxy nuclei, such as central mass deficits
and excess nuclear light, plus the structure of dark matter halos and cD galaxy
envelopes, are discussed. Issues pertaining to spiral galaxies including dust,
bulge-to-disc ratios, bulgeless galaxies, bars and the identification of
pseudobulges are also reviewed. An array of modern scaling relations involving
sizes, luminosities, surface brightnesses and stellar concentrations are
presented, many of which are shown to be curved. These 'redshift zero'
relations not only quantify the behavior and nature of galaxies in the Universe
today, but are the modern benchmark for evolutionary studies of galaxies,
whether based on observations, N-body-simulations or semi-analytical modelling.
For example, it is shown that some of the recently discovered compact
elliptical galaxies at 1.5 < z < 2.5 may be the bulges of modern disc galaxies.Comment: Condensed version (due to Contract) of an invited review article to
appear in "Planets, Stars and Stellar
Systems"(www.springer.com/astronomy/book/978-90-481-8818-5). 500+ references
incl. many somewhat forgotten, pioneer papers. Original submission to
Springer: 07-June-201
An optical group catalogue to z = 1 from the zCOSMOS 10k sample
We present a galaxy group catalogue spanning the redshift range 0.1 <~ z <~ 1
in the ~1.7 deg^2 COSMOS field, based on the first ~10,000 zCOSMOS spectra. The
performance of both the Friends-of-Friends (FOF) and Voronoi-Delaunay-Method
(VDM) approaches to group identification has been extensively explored and
compared using realistic mock catalogues. We find that the performance improves
substantially if groups are found by progressively optimizing the group-finding
parameters for successively smaller groups, and that the highest fidelity
catalogue, in terms of completeness and purity, is obtained by combining the
independently created FOF and VDM catalogues. The final completeness and purity
of this catalogue, both in terms of the groups and of individual members,
compares favorably with recent results in the literature. The current group
catalogue contains 102 groups with N >= 5 spectroscopically confirmed members,
with a further ~700 groups with 2 <= N <= 4. Most of the groups can be assigned
a velocity dispersion and a dark-matter mass derived from the mock catalogues,
with quantifiable uncertainties. The fraction of zCOSMOS galaxies in groups is
about 25% at low redshift and decreases toward ~15% at z ~ 0.8. The zCOSMOS
group catalogue is broadly consistent with that expected from the semi-analytic
evolution model underlying the mock catalogues. Not least, we show that the
number density of groups with a given intrinsic richness increases from
redshift z ~ 0.8 to the present, consistent with the hierarchical growth of
structure.Comment: 20 pages, 19 figures, accepted for publication in Ap
Mapping the dark side with DEIMOS: globular clusters, X-ray gas, and dark matter in the NGC 1407 group
NGC 1407 is the central elliptical in a nearby evolved group of galaxies apparently destined to become a galaxy cluster core. We use the kinematics of globular clusters (GCs) to probe the dynamics and mass profile of the group\u27s center, out to a radius of 60 kpc (~10 galaxy effective radii)âthe most extended data set to date around an early-type galaxy. This sample consists of 172 GC line-of-sight velocities, most of them newly obtained using Keck/DEIMOS, with a few additional objects identified as dwarf-globular transition objects or as intragroup GCs. We find weak rotation for the outer parts of the GC system (v/Ï ~ 0.2), with a rotational misalignment between the metal-poor and metal-rich GCs. The velocity dispersion profile declines rapidly to a radius of ~20 kpc, and then becomes flat or rising to ~60 kpc. There is evidence that the GC orbits have a tangential bias that is strongest for the metal-poor GCsâin possible contradiction to theoretical expectations. We construct cosmologically motivated galaxy+dark halo dynamical models and infer a total mass within 60 kpc of ~3 Ă 1012 M â, which extrapolates to a virial mass of ~6 Ă 1013 M â for a typical lambda cold dark matter (ÎCDM) haloâin agreement with results from kinematics of the group galaxies. We present an independent Chandra-based analysis, whose relatively high mass at ~20 kpc disagrees strongly with the GC-based result unless the GCs are assumed to have a peculiar orbit distribution, and we therefore discuss more generally some comparisons between X-ray and optical results. The group\u27s B-band mass-to-light ratio of ~800 (uncertain by a factor of ~2) in Solar units is extreme even for a rich galaxy cluster, much less a poor groupâplacing it among the most dark matter (DM) dominated systems in the universe, and also suggesting a massive reservoir of baryons lurking in an unseen phase, in addition to the nonbaryonic DM. We compare the kinematical and mass properties of the NGC 1407 group to other nearby groups and clusters, and discuss some implications of this system for structure formation