193 research outputs found
The Relation between Galaxy Structure and Spectral Type: Implications for the Buildup of the Quiescent Galaxy Population at 0.5<z<2.0
We present the relation between galaxy structure and spectral type, using a
K-selected galaxy sample at 0.5<z<2.0. Based on similarities between the
UV-to-NIR spectral energy distributions, we classify galaxies into 32 spectral
types. The different types span a wide range in evolutionary phases, and thus
-- in combination with available CANDELS/F160W imaging -- are ideal to study
the structural evolution of galaxies. Effective radii (R_e) and Sersic
parameters (n) have been measured for 572 individual galaxies, and for each
type, we determine R_e at fixed stellar mass by correcting for the mass-size
relation. We use the rest-frame U-V vs. V-J diagram to investigate evolutionary
trends. When moving into the direction perpendicular to the star-forming
sequence, in which we see the Halpha equivalent width and the specific star
formation rate (sSFR) decrease, we find a decrease in R_e and an increase in n.
On the quiescent sequence we find an opposite trend, with older redder galaxies
being larger. When splitting the sample into redshift bins, we find that young
post-starburst galaxies are most prevalent at z>1.5 and significantly smaller
than all other galaxy types at the same redshift. This result suggests that the
suppression of star formation may be associated with significant structural
evolution at z>1.5. At z<1, galaxy types with intermediate sSFRs
(10^{-11.5}-10^{-10.5} yr^-1) do not have post-starburst SED shapes. These
galaxies have similar sizes as older quiescent galaxies, implying that they can
passively evolve onto the quiescent sequence, without increasing the average
size of the quiescent galaxy population.Comment: 7 pages, 5 figures; Accepted for publication in ApJ
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
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
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