82 research outputs found
The Most Massive Galaxies at 3.0<z<4.0 in the NEWFIRM Medium-Band Survey: Properties and Improved Constraints on the Stellar Mass Function
[Abridged] We use the NEWFIRM Medium-Band Survey (NMBS) to characterize the
properties of a mass-complete sample of 14 galaxies at 3.0<z<4.0 with
M_star>2.5x10^11 Msun, and to derive more accurate measurements of the
high-mass end of the stellar mass function (SMF) of galaxies at z=3.5, with
significantly reduced contributions from photometric redshift errors and cosmic
variance to the total error budget of the SMF. The typical very massive galaxy
at z=3.5 is red and faint in the observer's optical, with median r=26.1, and
rest-frame U-V=1.6. About 60% of the sample have optical colors satisfying
either the U- or the B-dropout color criteria, although ~50% of these galaxies
have r>25.5. About 30% of the sample has SFRs from SED modeling consistent with
zero. However, >80% of the sample is detected at 24 micron, with total infrared
luminosities in the range (0.5-4.0)x10^13 Lsun. This implies the presence of
either dust-enshrouded starburst activity (with SFRs of 600-4300 Msun/yr)
and/or highly-obscured active galactic nuclei (AGN). The contribution of
galaxies with M_star>2.5x10^11 Msun to the total stellar mass budget at z=3.5
is ~8%. We find an evolution by a factor of 2-7 and 3-22 from z~5 and z~6,
respectively, to z=3.5. The previously found disagreement at the high-mass end
between observed and model-predicted SMFs is now significant at the 3sigma
level. However, systematic uncertainties dominate the total error budget, with
errors up to a factor of ~8 in the densities, bringing the observed SMF in
marginal agreement with the predicted SMF. Additional systematic uncertainties
on the high-mass end could be introduced by either 1) the intense
star-formation and/or the very common AGN activities as inferred from the MIPS
24 micron detections, and/or 2) contamination by a significant population of
massive, old, and dusty galaxies at z~2.6.Comment: 20 pages, 11 figures. Accepted in ApJ. Minor changes to colors of
figures to match accepted versio
Detection of quiescent galaxies in a bicolor sequence from z=0-2
We investigate the properties of quiescent and star-forming galaxy
populations to z~2 with purely photometric data, employing a novel rest-frame
color selection technique. From the UKIDSS Ultra-Deep Survey Data Release 1,
with matched optical and mid-IR photometry taken from the Subaru XMM Deep
Survey and Spitzer Wide-Area Infrared Extragalactic Survey respectively, we
construct a K-selected galaxy catalog and calculate photometric redshifts.
Excluding stars, objects with uncertain z_phot solutions, those that fall in
bad or incomplete survey regions, and those for which reliable rest-frame
colors could not be derived, 30108 galaxies with K<22.4 (AB) and z<2.5 remain.
The galaxies in this sample are found to occupy two distinct populations in the
rest-frame U-V vs. V-J color space: a clump of red, quiescent galaxies
(analogous to the red sequence) and a track of star-forming galaxies extending
from blue to red U-V colors. This bimodal behavior is seen up to z~2. Due to a
combination of measurement errors and passive evolution, the color-color
diagram is not suitable to distinguish the galaxy bimodality at z>2 for this
sample, but we show that MIPS 24um data suggest that a significant population
of quiescent galaxies exists even at these higher redshifts. At z=1-2, the most
luminous objects in the sample are divided roughly equally between star-forming
and quiescent galaxies, while at lower redshifts most of the brightest galaxies
are quiescent. Moreover, quiescent galaxies at these redshifts are clustered
more strongly than those actively forming stars, indicating that galaxies with
early-quenched star formation may occupy more massive host dark matter halos.
This suggests that the end of star formation is associated with, and perhaps
brought about by, a mechanism related to halo mass.Comment: 17 pages, 16 figures, accepted to ApJ after minor revisions. The
K-selected catalog described herein can be downloaded at
http://www.strw.leidenuniv.nl/galaxyevolution/UD
A Confirmation of the Strong Clustering of Distant Red Galaxies at 2 < z <3
Recent studies have shown that distant red galaxies (DRGs), which dominate
the high-mass end of the galaxy population at z~2.5, are more strongly
clustered than the population of blue star-forming galaxies at similar
redshifts. However these studies have been severely hampered by the small sizes
of fields having deep near-infrared imaging. Here we use the large UKIDSS Ultra
Deep Survey to study the clustering of DRGs. The size and depth of this survey
allows for an unprecedented measurement of the angular clustering of DRGs at
2<z_phot<3 and K<21. The correlation function shows the expected power law
behavior, but with an apparent upturn at theta<~10". We deproject the angular
clustering to infer the spatial correlation length, finding 10.6+-1.6 h^-1 Mpc.
We use the halo occupation distribution framework to demonstrate that the
observed strong clustering of DRGs is not consistent with standard models of
galaxy clustering, confirming previous suggestions that were based on smaller
samples. Inaccurate photometric redshifts could artificially enhance the
observed clustering, however significant systematic redshift errors would be
required to bring the measurements into agreement with the models. Another
possibility is that the underlying assumption that galaxies interact with their
large-scale environment only through halo mass is not valid, and that other
factors drive the evolution of the oldest, most massive galaxies at z~2.Comment: Accepted for publication in ApJ Letter
CLEAR I: Ages and Metallicities of Quiescent Galaxies at Derived from Deep Hubble Space Telescope Grism Data
We use deep \textit{Hubble Space Telescope} spectroscopy to constrain the
metallicities and (\editone{light-weighted}) ages of massive () galaxies selected to have quiescent stellar
populations at . The data include 12--orbit depth coverage with the
WFC3/G102 grism covering ~\AA\, at a spectral
resolution of taken as part of the CANDELS Lyman- Emission
at Reionization (CLEAR) survey. At , the spectra cover important
stellar population features in the rest-frame optical. We simulate a suite of
stellar population models at the grism resolution, fit these to the data for
each galaxy, and derive posterior likelihood distributions for metallicity and
age. We stack the posteriors for subgroups of galaxies in different redshift
ranges that include different combinations of stellar absorption features. Our
results give \editone{light-weighted ages of ~Gyr,
~Gyr, ~Gyr, and
~Gyr, \editone{for galaxies at , 1.2,
1.3, and 1.6. This} implies that most of the massive quiescent galaxies at
\% of their stellar mass by a redshift of }. The
posteriors give metallicities of \editone{~, ~, ~, and ~}. This is evidence
that massive galaxies had enriched rapidly to approximately Solar metallicities
as early as .Comment: 32 pages, 23 figures, Resubmited to ApJ after revisions in response
to referee repor
HST/WFC3 Confirmation of the Inside-Out Growth of Massive Galaxies at 0<z<2 and Identification of their Star Forming Progenitors at z~3
We study the structural evolution of massive galaxies by linking progenitors
and descendants at a constant cumulative number density of n_c=1.4x10^{-4}
Mpc^{-3} to z~3. Structural parameters were measured by fitting Sersic profiles
to high resolution CANDELS HST WFC3 J_{125} and H_{160} imaging in the
UKIDSS-UDS at 1<z<3 and ACS I_{814} imaging in COSMOS at 0.25<z<1. At a given
redshift, we selected the HST band that most closely samples a common
rest-frame wavelength so as to minimize systematics from color gradients in
galaxies. At fixed n_c, galaxies grow in stellar mass by a factor of ~3 from
z~3 to z~0. The size evolution is complex: galaxies appear roughly constant in
size from z~3 to z~2 and then grow rapidly to lower redshifts. The evolution in
the surface mass density profiles indicates that most of the mass at r<2 kpc
was in place by z~2, and that most of the new mass growth occurred at larger
radii. This inside-out mass growth is therefore responsible for the larger
sizes and higher Sersic indices of the descendants toward low redshift. At z<2,
the effective radius evolves with the stellar mass as r_e M^{2.0}, consistent
with scenarios that find dissipationless minor mergers to be a key driver of
size evolution. The progenitors at z~3 were likely star-forming disks with
r_e~2 kpc, based on their low Sersic index of n~1, low median axis ratio of
b/a~0.52, and typical location in the star-forming region of the U-V versus V-J
diagram. By z~1.5, many of these star-forming disks disappeared, giving rise to
compact quiescent galaxies. Toward lower redshifts, these galaxies continued to
assemble mass at larger radii and became the local ellipticals that dominate
the high mass end of the mass function at the present epoch.Comment: 12 pages, 8 figures in main text + appendix. v2 reflects the version
that was accepted to ApJ after addressing the referee repor
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