4 research outputs found
An Explanation for the Observed Weak Size Evolution of Disk Galaxies
Surveys of distant galaxies with the Hubble Space Telescope and from the
ground have shown that there is only mild evolution in the relationship between
radial size and stellar mass for galactic disks from z~1 to the present day.
Using a sample of nearby disk-dominated galaxies from the Sloan Digital Sky
Survey (SDSS), and high redshift data from the GEMS (Galaxy Evolution from
Morphology and SEDs) survey, we investigate whether this result is consistent
with theoretical expectations within the hierarchical paradigm of structure
formation. The relationship between virial radius and mass for dark matter
halos in the LCDM model evolves by about a factor of two over this interval.
However, N-body simulations have shown that halos of a given mass have less
centrally concentrated mass profiles at high redshift. When we compute the
expected disk size-stellar mass distribution, accounting for this evolution in
the internal structure of dark matter halos and the adiabatic contraction of
the dark matter by the self-gravity of the collapsing baryons, we find that the
predicted evolution in the mean size at fixed stellar mass since z~1 is about
15-20 percent, in good agreement with the observational constraints from GEMS.
At redshift z~2, the model predicts that disks at fixed stellar mass were on
average only 60% as large as they are today. Similarly, we predict that the
rotation velocity at a given stellar mass (essentially the zero-point of the
Tully-Fisher relation) is only about 10 percent larger at z~1 (20 percent at
z~2) than at the present day.Comment: 13 pages, 6 figures, accepted for publication in ApJ. Revised in
response to referee's comments to improve clariry. Results are unchange
GEMS: The Size Evolution of Disk Galaxies
We combine HST imaging from the GEMS survey with photometric redshifts from
COMBO-17 to explore the evolution of disk-dominated galaxies since z<1.1. The
sample is comprised of all GEMS galaxies with Sersic indices n<2.5, derived
from fits to the galaxy images. We account fully for selection effects through
careful analysis of image simulations; we are limited by the depth of the
redshift and HST data to the study of galaxies with absolute magnitudes
M(V)10. We find strong evolution in
the magnitude-size scaling relation for galaxies with M(V)<-20, corresponding
to a brightening of 1 mag per sqarcsec in rest-frame V-band by z=1. Yet, disks
at a given absolute magnitude are bluer and have lower stellar mass-to-light
ratios at z=1 than at the present day. As a result, our findings indicate weak
or no evolution in the relation between stellar mass and effective disk size
for galaxies with log(M)>10 over the same time interval. This is strongly
inconsistent with the most naive theoretical expectation, in which disk size
scales in proportion to the halo virial radius, which would predict that disks
are a factor of two denser at fixed mass at z=1. The lack of evolution in the
stellar mass-size relation is consistent with an ``inside-out'' growth of
galaxy disks on average (galaxies increasing in size as they grow more
massive), although we cannot rule out more complex evolutionary scenarios.Comment: 22 pages, 16 figures, submitted to Ap
The Evolution of Early-type Red Galaxies with the GEMS Survey: Luminosity-size and Stellar Mass-size Relations Since z=1
We combine HST/ACS imaging from the GEMS survey with redshifts and rest-frame
quantities from COMBO-17 to study the evolution of morphologically early-type
galaxies with red colors since z=1. We use a new large sample of 728 galaxies
with centrally-concentrated radial profiles (Sersic n>2.5) and rest-frame U-V
colors on the red sequence. By appropriate comparison with the local relations
from SDSS, we find that the luminosity-size (L-R) and stellar mass-size (M-R)
relations evolve in a manner that is consistent with the passive aging of
ancient stars. By itself, this result is consistent with a completely passive
evolution of the red early-type galaxy population. If instead, as demonstrated
by a number of recent surveys, the early-type galaxy population builds up in
mass by a factor of 2 since z=1, our results imply that new additions to the
early-type galaxy population follow similar L-R and M-R correlations, compared
to the older subset of early-type galaxies. Adding early-type galaxies to the
red sequence through disk fading appears to be consistent with the data.
Through comparison with models, the role of dissipationless merging is limited
to <1 major merger on average since z=1 for the most massive galaxies.
Predictions from models of gas-rich mergers are not yet mature enough to allow
a detailed comparison to our observations. We find tentative evidence that the
amount of luminosity evolution depends on galaxy stellar mass, such that the
least massive galaxies show stronger luminosity evolution compared to more
massive early types. This could reflect a different origin of low-mass
early-type galaxies and/or younger stellar populations; the present data is
insufficient to discriminate between these possibilities. (abridged)Comment: Submitted to ApJ, 23 pages, Latex using emulateapj5.sty and
onecolfloat.sty (included), 10 figures, version with full resolution figures
at http://www.astro.umass.edu/~dmac/Papers/ETevol.hires.p