35 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
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
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&
Relating basic properties of bright early-type dwarf galaxies to their location in Abell 901/902
We present a study of the population of bright early-type dwarf galaxies in
the multiple-cluster system Abell 901/902. We use data from the STAGES survey
and COMBO-17 to investigate the relation between the color and structural
properties of the dwarfs and their location in the cluster. The definition of
the dwarf sample is based on the central surface brightness and includes
galaxies in the luminosity range -16 >= M_B >~-19 mag. Using a fit to the color
magnitude relation of the dwarfs, our sample is divided into a red and blue
subsample. We find a color-density relation in the projected radial
distribution of the dwarf sample: at the same luminosity dwarfs with redder
colors are located closer to the cluster centers than their bluer counterparts.
Furthermore, the redder dwarfs are on average more compact and rounder than the
bluer dwarfs. These findings are consistent with theoretical expectations
assuming that bright early-type dwarfs are the remnants of transformed
late-type disk galaxies involving processes such as ram pressure stripping and
galaxy harassment. This indicates that a considerable fraction of dwarf
elliptical galaxies in clusters are the results of transformation processes
related to interactions with their host cluster.Comment: 12 pages, 8 figures, accepted for publication in A&A, typo corrected
in abstrac
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
Photometric scaling relations of lenticular and spiral galaxies
Photometric scaling relations are studied for S0 galaxies and compared with
those for spirals. New 2D K_s-band multi-component decompositions are presented
for 122 early-type disk galaxies. Combining with our previous decompositions,
the final sample consists of 175 galaxies. As a comparison sample we use the
Ohio State University Bright Spiral Galaxy Survey (OSUBSGS), for which similar
decompositions have previously been made by us. Our main results are: (1)
Important scaling relations are present, indicating that the formative
processes of bulges and disks in S0s are coupled like has been previously found
for spirals. (2) We obtain median r_{eff}/h_r = 0.20, 0.15 and 0.10 for S0,
S0/a-Sa and Sab-Sc galaxies: these are smaller than predicted by simulation
models in which bulges are formed by galaxy mergers. (3) The properties of
bulges of S0s are different from the elliptical galaxies, which is manifested
in the M_K(bulge) vs r_{eff} relation, in the photometric plane, and to some
extent also in the Kormendy relation. The bulges of S0s are similar to bulges
of spirals with M_K(bulge) < -20 mag. Some S0s have small bulges, but their
properties are not compatible with the idea that they could evolve to dwarfs by
galaxy harassment. (4) The relative bulge flux B/T for S0s covers the full
range found in the Hubble sequence. (5) The values and relations of the
parameters of the disks of the S0 galaxies in NIRS0S are similar to those
obtained for spirals in the OSUBSGS. Overall, our results support the view that
spiral galaxies with bulges brighter than -20 mag in the K-band can evolve
directly into S0s, due to stripping of gas followed by truncated star
formation.Comment: Accepted to MNRAS, includes a big figure in electronic form, not
included her
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