654 research outputs found
Half-mass radii for ~7,000 galaxies at 1.0 < z < 2.5: most of the evolution in the mass-size relation is due to color gradients
Radial mass-to-light ratio gradients cause the half-mass and half-light radii
of galaxies to differ, potentially biasing studies that use half-light radii.
Here we present the largest catalog to date of galaxy half-mass radii at z > 1:
7,006 galaxies in the CANDELS fields at 1.0 < z < 2.5. The sample includes both
star-forming and quiescent galaxies with stellar masses 9.0 < log(M_* /
M_\odot) < 11.5. We test three methods for calculating half-mass radii from
multi-band PSF-matched HST imaging: two based on spatially-resolved SED
modeling, and one that uses a rest-frame color profile. All three methods
agree, with scatter <~0.3 dex. In agreement with previous studies, most
galaxies in our sample have negative color gradients (the centers are redder
than the outskirts, and r_e,mass < r_e,light). We find that color gradient
strength has significant trends with increasing stellar mass, half-light
radius, U-V color, and stellar mass surface density. These trends have not been
seen before at z>1. Furthermore, color gradients of star-forming and quiescent
galaxies show a similar redshift evolution: they are flat at z>~2, then steeply
decrease as redshift decreases. This affects the galaxy mass-size relation. The
normalizations of the star-forming and quiescent r_mass-M_* relations are
10-40% smaller than the corresponding r_light-M_* relations; the slopes are
~0.1-0.3 dex shallower. Finally, the half-mass radii of star-forming and
quiescent galaxies at M_* = 10^{10.5}M_\odot only grow by ~1%$ and ~8% between
z~2.25 and z~1.25. This is significantly less than the ~37% and ~47% size
increases found when using the half-light radius.Comment: 18 pages, 10 figures. Accepted to Ap
Testing the Recovery of Intrinsic Galaxy Sizes and Masses of z~2 Massive Galaxies Using Cosmological Simulations
Accurate measurements of galaxy masses and sizes are key to tracing galaxy
evolution over time. Cosmological zoom-in simulations provide an ideal test bed
for assessing the recovery of galaxy properties from observations. Here, we
utilize galaxies with at z~1.7-2 from the
MassiveFIRE cosmological simulation suite, part of the Feedback in Realistic
Environments (FIRE) project. Using mock multi-band images, we compare intrinsic
galaxy masses and sizes to observational estimates. We find that observations
accurately recover stellar masses, with a slight average underestimate of ~0.06
dex and a ~0.15 dex scatter. Recovered half-light radii agree well with
intrinsic half-mass radii when averaged over all viewing angles, with a
systematic offset of ~0.1 dex (with the half-light radii being larger) and a
scatter of ~0.2 dex. When using color gradients to account for mass-to-light
variations, recovered half-mass radii also exceed the intrinsic half-mass radii
by ~0.1 dex. However, if not properly accounted for, aperture effects can bias
size estimates by ~0.1 dex. No differences are found between the mass and size
offsets for star-forming and quiescent galaxies. Variations in viewing angle
are responsible for ~25% of the scatter in the recovered masses and sizes. Our
results thus suggest that the intrinsic scatter in the mass-size relation may
have previously been overestimated by ~25%. Moreover, orientation-driven
scatter causes the number density of very massive galaxies to be overestimated
by ~0.5 dex at .Comment: Published in the Astrophysical Journal Letters (7 pages, 5 figures;
updated to match published version
Color gradients along the quiescent galaxy sequence: clues to quenching and structural growth
This Letter examines how the sizes, structures, and color gradients of
galaxies change along the quiescent sequence. Our sample consists of ~400
quiescent galaxies at and
in three CANDELS fields. We exploit deep multi-band HST imaging to derive
accurate mass profiles and color gradients, then use an empirical calibration
from rest-frame UVJ colors to estimate galaxy ages. We find that -- contrary to
previous results -- the youngest quiescent galaxies are not significantly
smaller than older quiescent galaxies at fixed stellar mass. These
`post-starburst' galaxies only appear smaller in half-light radii because they
have systematically flatter color gradients. The strength of color gradients in
quiescent galaxies is a clear function of age, with older galaxies exhibiting
stronger negative color gradients (i.e., redder centers). Furthermore, we find
that the central mass surface density is independent of age at fixed
stellar mass, and only weakly depends on redshift. This finding implies that
the central mass profiles of quiescent galaxies do not significantly change
with age; however, we find that older quiescent galaxies have additional mass
at large radii. Our results support the idea that building a massive core is a
necessary requirement for quenching beyond , and indicate that
post-starburst galaxies are the result of a rapid quenching process that
requires structural change. Furthermore, our observed color gradient and mass
profile evolution supports a scenario where quiescent galaxies grow inside-out
via minor mergers.Comment: 7 pages, 5 figures. Accepted to ApJ
Trained and Amphetamine-Induced Circling Behavior in Lesioned, Transplanted Rats
Rats were trained to turn for water
reinforcement and then were given unilateral 6-
hydroxydopamine lesions. After lesion, rats
showed deficits in trained turning both contraand
ipsilateral to the side of the lesion, with
contralateral turning more severely impaired.
The lesioned rats were then transplanted with
fetal mesencephalic dopamine tissue into
striatum. A control group of lesioned rats were
sham transplanted. Four weeks after transplant,
1.5 mg/kg D-amphetamine challenge injections
were used to test the functioning of the
transplants. In the control rats, D-amphetamine
induced ipsilateral turning; in transplanted rats,
D-amphetamine slowed the rate of ipsilateral
turning or reversed the direction of
amphetamine-induced rotation. Only rats which
reversed their, amphetamine-induced turn
direction after transplant were used for the rest
of the experiment. Trained turning was assessed
at 4, 8, 12 and 16 weeks post transplant.
Transplants did not improve learned
performance at any time post transplant. When
D-amphetamine was administered in
conjunction with the trained turning sessions, a
low dose (0.12 mg/kg) enhanced contralateral
trained turn rates, without affecting ipsilateral
turn rates. Higher doses of amphetamine
reduced ipsilateral turn rate in the transplanted
animals. The results of this study suggest that
transplants alone do not reinstate performance
of conditioned rotation
The Detection of a Red Sequence of Massive Field Galaxies at z~2.3 and its Evolution to z~0
The existence of massive galaxies with strongly suppressed star formation at
z~2.3, identified in a previous paper, suggests that a red sequence may already
be in place beyond z=2. In order to test this hypothesis, we study the
rest-frame U-B color distribution of massive galaxies at 2<z<3. The sample is
drawn from our near-infrared spectroscopic survey for massive galaxies. The
color distribution shows a statistically significant (>3 sigma) red sequence,
which hosts ~60% of the stellar mass at the high-mass end. The red-sequence
galaxies have little or no ongoing star formation, as inferred from both
emission-line diagnostics and stellar continuum shapes. Their strong Balmer
breaks and their location in the rest-frame U-B, B-V plane indicate that they
are in a post-starburst phase, with typical ages of ~0.5-1.0 Gyr. In order to
study the evolution of the red sequence, we compare our sample with
spectroscopic massive galaxy samples at 0.02<z<0.045 and 0.6<z<1.0. The
rest-frame U-B color reddens by ~0.25 mag from z~2.3 to the present at a given
mass. Over the same redshift interval, the number and stellar mass density on
the high-mass end (>10^11 Msol) of the red sequence grow by factors of ~8 and
~6, respectively. We explore simple models to explain the observed evolution.
Passive evolution models predict too strong d(U-B), and produce z~0 galaxies
that are too red. More complicated models that include aging, galaxy
transformations, and red mergers can explain both the number density and color
evolution of the massive end of the red sequence between z~2.3 and the present.Comment: Accepted for publication in the Astrophysical Journa
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