176 research outputs found
Clustering of Intermediate Luminosity X-ray selected AGN at z~3
We present the first clustering results of X-ray selected AGN at z~3. Using
Chandra X-ray imaging and UVR optical colors from MUSYC photometry in the
ECDF-S field, we selected a sample of 58 z~3 AGN candidates. From the optical
data we also selected 1385 LBG at 2.8<z< 3.8 with R<25.5. We performed
auto-correlation and cross-correlation analyses, and here we present results
for the clustering amplitudes and dark matter halo masses of each sample. For
the LBG we find a correlation length of r_0,LBG = 6.7 +/- 0.5 Mpc, implying a
bias value of 3.5 +/- 0.3 and dark matter (DM) halo masses of log(Mmin/Msun) =
11.8 +/- 0.1. The AGN-LBG cross-correlation yields r_0,AGN-LBG = 8.7 +/- 1.9
Mpc, implying for AGN at 2.8<z<3.8 a bias value of 5.5 +/- 2.0 and DM halo
masses of log(Mmin/Msun) = 12.6 +0.5/-0.8. Evolution of dark matter halos in
the Lambda CDM cosmology implies that today these z~3 AGN are found in high
mass galaxies with a typical luminosity of 7+4/-2 L*.Comment: Accepted for publication in ApJ Letters. 4 pages, 4 figures (1 in
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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
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
The Multiwavelength Survey By Yale-Chile (MUSYC) Wide K-Band Imaging, Photometric Catalogs, Clustering, And Physical Properties Of Galaxies At Z Similar To 2
We present K-band imaging of two similar to 30' x 30' fields covered by the Multiwavelength Survey by Yale-Chile (MUSYC) Wide NIR Survey. The SDSS 1030+05 and Cast 1255 fields were imaged with the Infrared Side Port Imager (ISPI) on the 4 m Blanco telescope at the Cerro Tololo Inter-American Observatory (CTIO) to a 5 sigma point-source limiting depth of K similar to 20 (Vega). Combining these data with the MUSYC optical UBVRIz imaging, we created multiband K-selected source catalogs for both fields. These catalogs, together with the MUSYC K-band catalog of the Extended Chandra Deep Field South (ECDF-S) field, were used to select K 20 BzK galaxies over an area of 0.71 deg(2). This is the largest area ever surveyed for BzK galaxies. We present number counts, redshift distributions, and stellar masses for our sample of 3261 BzK galaxies (2502 star-forming [sBzK] and 759 passively evolving [pBzK]), as well as reddening and star formation rate estimates for the star-forming BzK systems. We also present two-point angular correlation functions and spatial correlation lengths for both sBzK and pBzK galaxies and show that previous estimates of the correlation function of these galaxies were affected by cosmic variance due to the small areas surveyed. We have measured correlation lengths r(0) of 8.89 +/- 2.03 and 10.82 +/- 1.72 Mpc for sBzK and pBzK galaxies, respectively. This is the first reported measurement of the spatial correlation function of passive BzK galaxies. In the Lambda CDM scenario of galaxy formation, these correlation lengths at z similar to 2 translate into minimum masses of similar to 4 x 10(12) and similar to 9 x 10(12) M(circle dot) for the dark matter halos hosting sBzK and pBzK galaxies, respectively. The clustering properties of the galaxies in our sample are consistent with their being the descendants of bright Lyman break galaxies at z similar to 3, and the progenitors of present-day > 1L* galaxies.Astronom
Direct Measurements of the Stellar Continua and Balmer/4000 Angstrom Breaks of Red z>2 Galaxies: Redshifts and Improved Constraints on Stellar Populations
We use near-infrared (NIR) spectroscopy obtained with GNIRS on Gemini,
NIRSPEC on KECK, and ISAAC on the VLT to study the rest-frame optical continua
of three `Distant Red Galaxies' (having Js - Ks > 2.3) at z>2. All three galaxy
spectra show the Balmer/4000 Angstrom break in the rest-frame optical. The
spectra allow us to determine spectroscopic redshifts from the continuum with
an estimated accuracy dz/(1+z) ~ 0.001-0.04. These redshifts agree well with
the emission line redshifts for the 2 galaxies with Halpha emission. This
technique is particularly important for galaxies that are faint in the
rest-frame UV, as they are underrepresented in high redshift samples selected
in optical surveys and are too faint for optical spectroscopy. Furthermore, we
use the break, continuum shape, and equivalent width of Halpha together with
evolutionary synthesis models to constrain the age, star formation timescale,
dust content, stellar mass and star formation rate of the galaxies. Inclusion
of the NIR spectra in the stellar population fits greatly reduces the range of
possible solutions for stellar population properties. We find that the stellar
populations differ greatly among the three galaxies, ranging from a young dusty
starburst with a small break and strong emission lines to an evolved galaxy
with a strong break and no detected line emission. The dusty starburst galaxy
has an age of 0.3 Gyr and a stellar mass of 1*10^11 Msun. The spectra of the
two most evolved galaxies imply ages of 1.3-1.4 Gyr and stellar masses of
4*10^11 Msun. The large range of properties seen in these galaxies strengthens
our previous much more uncertain results from broadband photometry. Larger
samples are required to determine the relative frequency of dusty starbursts
and (nearly) passively evolving galaxies at z~2.5.Comment: Accepted for publication in the Astrophysical Journal. 12 pages, 6
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