362 research outputs found
Bulge plus disc and S\'ersic decomposition catalogues for 16,908 galaxies in the SDSS Stripe 82 co-adds: A detailed study of the structural measurements
Quantitative characterization of galaxy morphology is vital in enabling
comparison of observations to predictions from galaxy formation theory.
However, without significant overlap between the observational footprints of
deep and shallow galaxy surveys, the extent to which structural measurements
for large galaxy samples are robust to image quality (e.g., depth, spatial
resolution) cannot be established. Deep images from the Sloan Digital Sky
Survey (SDSS) Stripe 82 co-adds provide a unique solution to this problem -
offering magnitudes improvement in depth with respect to SDSS Legacy
images. Having similar spatial resolution to Legacy, the co-adds make it
possible to examine the sensitivity of parametric morphologies to depth alone.
Using the Gim2D surface-brightness decomposition software, we provide public
morphology catalogs for 16,908 galaxies in the Stripe 82 co-adds. Our
methods and selection are completely consistent with the Simard et al. (2011)
and Mendel et al. (2014) photometric decompositions. We rigorously compare
measurements in the deep and shallow images. We find no systematics in total
magnitudes and sizes except for faint galaxies in the -band and the
brightest galaxies in each band. However, characterization of bulge-to-total
fractions is significantly improved in the deep images. Furthermore, statistics
used to determine whether single-S\'ersic or two-component (e.g., bulge+disc)
models are required become more bimodal in the deep images. Lastly, we show
that asymmetries are enhanced in the deep images and that the enhancement is
positively correlated with the asymmetries measured in Legacy images.Comment: 27 pages, 14 figures. MNRAS accepted. Our catalogs are available in
TXT and SQL formats at
http://orca.phys.uvic.ca/~cbottrel/share/Stripe82/Catalogs
Stellar mass functions of galaxies, disks and spheroids at z~0.1
We present the stellar mass functions (SMF) and mass densities of galaxies,
and their spheroid and disk components in the local (z~0.1) universe over the
range 8.9 <= log(M/M_solar) <= 12 from spheroid+disk decompositions and
corresponding stellar masses of a sample of over 600,000 galaxies in the
SDSS-DR7 spectroscopic sample. The galaxy SMF is well represented by a single
Schechter function (M* = 11.116+/-0.011, alpha = -1.145+/-0.008), though with a
hint of a steeper faint end slope. The corresponding stellar mass densities are
(2.670+/-0.110), (1.687+/-0.063) and (0.910+/-0.029)x10^8 M_solar Mpc^-3 for
galaxies, spheroids and disks respectively. We identify a crossover stellar
mass of log(M/M_solar) = 10.3+/-0.030 at which the spheroid and disk SMFs are
equal. Relative contributions of four distinct spheroid/disk dominated
sub-populations to the overall galaxy SMF are also presented. The mean
disk-to-spheroid stellar mass ratio shows a five fold disk dominance at the low
mass end, decreasing monotonically with a corresponding increase in the
spheroidal fraction till the two are equal at a galaxy stellar mass,
log(M/M_solar)=10.479+/-0.013, the dominance of spheroids then grows with
increasing stellar mass. The relative numbers of composite disk and spheroid
dominated galaxies show peaks in their distributions, perhaps indicative of a
preferred galaxy mass. Our characterization of the low redshift galaxy
population provides stringent constraints for numerical simulations to
reproduce.Comment: 30 pages, 18 figures, 5 tables (2 online), Accepted for publication
in MNRA
The signature of dissipation in the mass-size relation: are bulges simply spheroids wrapped in a disc?
The relation between the stellar mass and size of a galaxy's structural
subcomponents, such as discs and spheroids, is a powerful way to understand the
processes involved in their formation. Using very large catalogues of
photometric bulge+disc structural decompositions and stellar masses from the
Sloan Digital Sky Survey Data Release Seven, we carefully define two large
subsamples of spheroids in a quantitative manner such that both samples share
similar characteristics with one important exception: the 'bulges' are embedded
in a disc and the 'pure spheroids' are galaxies with a single structural
component. Our bulge and pure spheroid subsample sizes are 76,012 and 171,243
respectively. Above a stellar mass of ~ M, the mass-size
relations of both subsamples are parallel to one another and are close to lines
of constant surface mass density. However, the relations are offset by a factor
of 1.4, which may be explained by the dominance of dissipation in their
formation processes. Whereas the size-mass relation of bulges in discs is
consistent with gas-rich mergers, pure spheroids appear to have been formed via
a combination of 'dry' and 'wet' mergers.Comment: Accepted for publication in MNRAS, 6 pages, 3 figure
Clues to the Origin of the Mass-Metallicity Relation: Dependence on Star Formation Rate and Galaxy Size
We use a sample of 43,690 galaxies selected from the Sloan Digital Sky Survey
Data Release 4 to study the systematic effects of specific star formation rate
(SSFR) and galaxy size (as measured by the half light radius, r_h) on the
mass-metallicity relation. We find that galaxies with high SSFR or large r_h
for their stellar mass have systematically lower gas phase-metallicities (by up
to 0.2 dex) than galaxies with low SSFR or small r_h. We discuss possible
origins for these dependencies, including galactic winds/outflows, abundance
gradients, environment and star formation rate efficiencies.Comment: Accepted by ApJ Letter
The Instrumentation Program for the Thirty Meter Telescope
An overview of the current status of the Thirty Meter Telescope (TMT) instrumentation program is presented. Science cases and operational concepts as well as their links to the instruments are continually revisited and updated through a series of workshops and conferences. Work on the three first-light instruments (WFOS IRIS, and IRMS) has made significant progress, and many groups in TMT partner communities are developing future instrument concepts. Other instrument-related subsystems are also receiving considerable attention given their importance to the scientific end-to-end performance of the Observatory. As an example, we describe aspects of the facility instrument cooling system that are crucially important to successful diffraction-limited observations on an extremely large telescope
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