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Richard J. Cool,
John Moustakas,
Michael R. Blanton,
Scott M. Burles,
Alison L. Coil,
Daniel J. Eisenstein,
Kenneth C. Wong,
Guangtun Zhu,
James Aird,
Rebecca A. Bernstein,
Adam S. Bolton,
David W. Hogg,
Alexander J. Mendez
[show abstract]
[hide abstract]
ABSTRACT: The PRIsm MUti-object Survey (PRIMUS) is a spectroscopic galaxy redshift
survey to z~1 completed with a low-dispersion prism and slitmasks allowing for
simultaneous observations of ~2,500 objects over 0.18 square degrees. The final
PRIMUS catalog includes ~130,000 robust redshifts over 9.1 sq. deg. In this
paper, we summarize the PRIMUS observational strategy and present the data
reduction details used to measure redshifts, redshift precision, and survey
completeness. The survey motivation, observational techniques, fields, target
selection, slitmask design, and observations are presented in Coil et al 2010.
Comparisons to existing higher-resolution spectroscopic measurements show a
typical precision of sigma_z/(1+z)=0.005. PRIMUS, both in area and number of
redshifts, is the largest faint galaxy redshift survey completed to date and is
allowing for precise measurements of the relationship between AGNs and their
hosts, the effects of environment on galaxy evolution, and the build up of
galactic systems over the latter half of cosmic history.
03/2013;
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[show abstract]
[hide abstract]
ABSTRACT: We present a study of Spitzer/IRAC and X-ray active galactic nuclei (AGNs)
selection techniques in order to quantify the overlap, uniqueness,
contamination, and completeness of each. We investigate how the overlap and
possible contamination of the samples depends on the IR and X-ray depths. We
use Spitzer/IRAC imaging, Chandra and XMM X-ray imaging, and PRism MUlti-object
Survey (PRIMUS) spectroscopic redshifts to construct galaxy and AGN samples at
0.2<z<1.2 over 8 deg^2. We construct samples over a wide range of IRAC flux
limits (SWIRE to GOODS depth) and X-ray flux limits (10 ks to 2 Ms). We compare
IR-AGN samples defined using the IRAC color selection of Stern et al. and
Donley et al. with X-ray detected AGN samples. For roughly similar depth IR and
X-ray surveys, we find that ~75% of IR-AGN are identified as X-ray AGN. This
fraction increases to ~90% when comparing against the deepest X-ray data,
indicating that only ~10% of IR-selected AGN may be heavily obscured. The
IR-AGN selection proposed by Stern et al. suffers from contamination by
star-forming galaxies at various redshifts when using deeper IR data, though
the selection technique works well for shallow IR data. While similar overall,
the IR-AGN samples preferentially contain more luminous AGN, while the X-ray
AGN samples preferentially contain lower specific accretion rate AGN, where the
host galaxy light dominates at IR wavelengths. The host galaxy populations of
the IR and X-ray AGN samples have similar restframe colors and stellar masses;
both selections identify AGN in blue, star-forming and red, quiescent galaxies.
02/2013;
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[show abstract]
[hide abstract]
ABSTRACT: We measure the evolution of the stellar mass function (SMF) from z=0-1 using
multi-wavelength imaging and spectroscopic redshifts from the PRism
MUlti-object Survey (PRIMUS) and the Sloan Digital Sky Survey (SDSS). From
PRIMUS we construct an i<23 flux-limited sample of ~40,000 galaxies at
z=0.2-1.0 over five fields totaling ~5.5 deg^2, and from the SDSS we select
~170,000 galaxies at z=0.01-0.2 that we analyze consistently with respect to
PRIMUS to minimize systematic errors in our evolutionary measurements. We find
that the SMF of all galaxies evolves relatively little since z=1, although we
do find evidence for mass assembly downsizing; we measure a ~30% increase in
the number density of ~10^10 Msun galaxies since z~0.6, and a <10% change in
the number density of all >10^11 Msun galaxies since z~1. Dividing the sample
into star-forming and quiescent using an evolving cut in specific
star-formation rate, we find that the number density of ~10^10 Msun
star-forming galaxies stays relatively constant since z~0.6, whereas the
space-density of >10^11 Msun star-forming galaxies decreases by ~50% between
z~1 and z~0. Meanwhile, the number density of ~10^10 Msun quiescent galaxies
increases steeply towards low redshift, by a factor of ~2-3 since z~0.6, while
the number of massive quiescent galaxies remains approximately constant since
z~1. These results suggest that the rate at which star-forming galaxies are
quenched increases with decreasing stellar mass, but that the bulk of the
stellar mass buildup within the quiescent population occurs around ~10^10.8
Msun. In addition, we conclude that mergers do not appear to be a dominant
channel for the stellar mass buildup of galaxies at z<1, even among massive
(>10^11 Msun) quiescent galaxies.
01/2013;
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[show abstract]
[hide abstract]
ABSTRACT: We present an observationally motivated model to connect the AGN and galaxy
populations at 0.2<z<1.0 and predict the AGN X-ray luminosity function (XLF).
We start with measurements of the stellar mass function of galaxies (from the
Prism Multi-object Survey) and populate galaxies with AGNs using models for the
probability of a galaxy hosting an AGN as a function of specific accretion rate
(the rate of supermassive black hole growth scaled relative to the host stellar
mass). Our model is based on measurements indicating that the specific
accretion rate distribution is a universal function across a wide range of host
stellar mass with slope gamma_1=0.65 and an overall normalization that evolves
strongly with redshift. We test several simple assumptions to extend this model
to high specific accretion rates (beyond the measurements) and compare the
predictions for the XLF with the observed data. We find good agreement with a
model that allows for a break in the specific accretion rate distribution at a
point corresponding to the Eddington limit, with a steep power-law tail to
super-Eddington ratios with slope gamma_2=-2.1 +0.3 -0.5. We convert between
specific accretion rate and Eddington ratio by assuming a scaling between black
hole mass and host stellar mass with an intrinsic scatter of +/-0.38 dex. Our
results show that samples of low luminosity AGNs are dominated by moderately
massive galaxies (M* ~ 10^{10-11} M_sun) growing with a wide range of accretion
rates -- a consequence of the shape of the galaxy stellar mass function rather
than a preference for AGN activity at a particular stellar mass. The observed
population of the most luminous AGN may be severely skewed to the most extreme
sources with elevated black hole masses relative to their host galaxies and in
rare phases of very rapid accretion.
01/2013;
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Richard J. Cool,
Daniel J. Eisenstein,
Christopher S. Kochanek,
Michael J. I. Brown,
Nelson Caldwell,
Arjun Dey,
William R. Forman,
Ryan C. Hickox,
Buell T. Jannuzi,
Christine Jones,
John Moustakas,
and Stephen S. Murray
[show abstract]
[hide abstract]
ABSTRACT: We present the galaxy optical luminosity function for the redshift range 0.05 < z < 0.75 from the AGN and Galaxy Evolution Survey, a spectroscopic survey of 7.6 deg2 in the Boötes field of the NOAO Deep Wide-Field Survey. Our statistical sample is composed of 12,473 galaxies with known redshifts down to I = 20.4 (AB). Our results at low redshift are consistent with those from Sloan Digital Sky Survey; at higher redshift, we find strong evidence for evolution in the luminosity function, including differential evolution between blue and red galaxies. We find that the luminosity density evolves as (1 + z)(0.54 ± 0.64) for red galaxies and (1 + z)(1.64 ± 0.39) for blue galaxies.
The Astrophysical Journal 02/2012; 748(1):10. · 6.02 Impact Factor
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[show abstract]
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ABSTRACT: We present evidence that the incidence of active galactic nuclei (AGNs) and the distribution of their accretion rates do not depend on the stellar masses of their host galaxies, contrary to previous studies. We use hard (2-10 keV) X-ray data from three extragalactic fields (XMM-LSS, COSMOS, and ELAIS-S1) with redshifts from the Prism Multi-object Survey to identify 242 AGNs with L 2-10 keV = 1042-44 erg s–1 within a parent sample of ~25,000 galaxies at 0.2 < z < 1.0 over ~3.4 deg2 and to i ~ 23. We find that although the fraction of galaxies hosting an AGN at fixed X-ray luminosity rises strongly with stellar mass, the distribution of X-ray luminosities is independent of mass. Furthermore, we show that the probability that a galaxy will host an AGN can be defined by a universal Eddington ratio distribution that is independent of the host galaxy stellar mass and has a power-law shape with slope –0.65. These results demonstrate that AGNs are prevalent at all stellar masses in the range and that the same physical processes regulate AGN activity in all galaxies in this stellar mass range. While a higher AGN fraction may be observed in massive galaxies, this is a selection effect related to the underlying Eddington ratio distribution. We also find that the AGN fraction drops rapidly between z ~ 1 and the present day and is moderately enhanced (factor ~2) in galaxies with blue or green optical colors. Consequently, while AGN activity and star formation appear to be globally correlated, we do not find evidence that the presence of an AGN is related to the quenching of star formation or the color transformation of galaxies.
The Astrophysical Journal 01/2012; 746(1):90. · 6.02 Impact Factor
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Richard J. Cool,
Daniel J. Eisenstein,
Christopher S. Kochanek,
Michael J. I. Brown,
Nelson Caldwell,
Arjun Dey,
William R. Forman,
Ryan C. Hickox,
Buell T. Jannuzi,
Christine Jones,
John Moustakas,
Stephen S. Murray
[show abstract]
[hide abstract]
ABSTRACT: We present the galaxy optical luminosity function for the redshift range
0.05<z<0.75 from the AGN and Galaxy Evolution Survey (AGES), a spectroscopic
survey of 7.6 sq. deg. in the Bootes field of the NOAO Deep Wide-Field Survey.
Our statistical sample is comprised of 12,473 galaxies with known redshifts
down to I=20.4 (AB). Our results at low redshift are consistent with those from
SDSS; at higher redshift, we find strong evidence for evolution in the
luminosity function, including differential evolution between blue and red
galaxies. We find that the luminosity density evolves as (1+z)^(0.54+/-0.64)
for red galaxies and (1+z)^(1.64+/-0.39) for blue galaxies.
01/2012;
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Alison L. Coil,
Michael R. Blanton,
Scott M. Burles, Richard J. Cool,
Daniel J. Eisenstein,
John Moustakas,
Kenneth C. Wong,
Guangtun Zhu,
James Aird,
Rebecca A. Bernstein,
Adam S. Bolton,
and David W. Hogg
[show abstract]
[hide abstract]
ABSTRACT: We present the PRIsm MUlti-object Survey (PRIMUS), a spectroscopic faint galaxy redshift survey to z ~ 1. PRIMUS uses a low-dispersion prism and slitmasks to observe ~2500 objects at once in a 0.18 deg2 field of view, using the Inamori Magellan Areal Camera and Spectrograph camera on the Magellan I Baade 6.5 m telescope at Las Campanas Observatory. PRIMUS covers a total of 9.1 deg2 of sky to a depth of i AB ~ 23.5 in seven different deep, multi-wavelength fields that have coverage from the Galaxy Evolution Explorer, Spitzer, and either XMM or Chandra, as well as multiple-band optical and near-IR coverage. PRIMUS includes ~130,000 robust redshifts of unique objects with a redshift precision of σ z /(1 + z) ~ 0.005. The redshift distribution peaks at z ~ 0.6 and extends to z = 1.2 for galaxies and z = 5 for broad-line active galactic nuclei. The motivation, observational techniques, fields, target selection, slitmask design, and observations are presented here, with a brief summary of the redshift precision; a forthcoming paper presents the data reduction, redshift fitting, redshift confidence, and survey completeness. PRIMUS is the largest faint galaxy survey undertaken to date. The high targeting fraction (~80%) and large survey size will allow for precise measures of galaxy properties and large-scale structure to z ~ 1.
The Astrophysical Journal 10/2011; 741(1):8. · 6.02 Impact Factor
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Ryan C. Hickox,
Adam D. Myers,
Mark Brodwin,
David M. Alexander,
William R. Forman,
Christine Jones,
Stephen S. Murray,
Michael J. I. Brown, Richard J. Cool,
Christopher S. Kochanek, [......],
Buell T. Jannuzi,
Daniel Eisenstein,
Roberto J. Assef,
Peter R. Eisenhardt,
Varoujan Gorjian,
Daniel Stern,
Emeric Le Floc'h,
Nelson Caldwell,
Andrew D. Goulding,
and James R. Mullaney
[show abstract]
[hide abstract]
ABSTRACT: We present the first measurement of the spatial clustering of mid-infrared-selected obscured and unobscured quasars, using a sample in the redshift range 0.7 < z < 1.8 selected from the 9 deg2 Boötes multiwavelength survey. Recently, the Spitzer Space Telescope and X-ray observations have revealed large populations of obscured quasars that have been inferred from models of the X-ray background and supermassive black hole evolution. To date, little is known about obscured quasar clustering, which allows us to measure the masses of their host dark matter halos and explore their role in the cosmic evolution of black holes and galaxies. In this study, we use a sample of 806 mid-infrared-selected quasars and 250,000 galaxies to calculate the projected quasar-galaxy cross-correlation function wp (R). The observed clustering yields characteristic dark matter halo masses of log(M halo [h –1 M ☉]) = 12.7+0.4 –0.6 and 13.3+0.3 –0.4 for unobscured quasars (QSO-1s) and obscured quasars (Obs-QSOs), respectively. The results for QSO-1s are in excellent agreement with previous measurements for optically selected quasars, while we conclude that the Obs-QSOs are at least as strongly clustered as the QSO-1s. We test for the effects of photometric redshift errors on the optically faint Obs-QSOs, and find that our method yields a robust lower limit on the clustering; photo-z errors may cause us to underestimate the clustering amplitude of the Obs-QSOs by at most ~20%. We compare our results to previous studies, and speculate on physical implications of stronger clustering for obscured quasars.
The Astrophysical Journal 03/2011; 731(2):117. · 6.02 Impact Factor
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Ryan C. Hickox,
Adam D. Myers,
Mark Brodwin,
David M. Alexander,
William R. Forman,
Christine Jones,
Stephen S. Murray,
Michael J. I. Brown, Richard J. Cool,
Roberto J. Assef, [......],
Arjun Dey,
Buell T. Jannuzi,
Daniel Eisenstein,
Peter R. Eisenhardt,
Varoujan Gorjian,
Daniel Stern,
Emeric Le Floc'h,
Nelson Caldwell,
Andrew D. Goulding,
James R. Mullaney
[show abstract]
[hide abstract]
ABSTRACT: We present the first measurement of the spatial clustering of mid-infrared
selected obscured and unobscured quasars, using a sample in the redshift range
0.7 < z < 1.8 selected from the 9 deg^2 Bootes multiwavelength survey. Recently
the Spitzer Space Telescope and X-ray observations have revealed large
populations of obscured quasars that have been inferred from models of the
X-ray background and supermassive black hole evolution. To date, little is
known about obscured quasar clustering, which allows us to measure the masses
of their host dark matter halos and explore their role in the cosmic evolution
of black holes and galaxies. In this study we use a sample of 806 mid-infrared
selected quasars and ~250,000 galaxies to calculate the projected quasar-galaxy
cross-correlation function w_p(R). The observed clustering yields
characteristic dark matter halo masses of log (M_halo [h^-1 M_sun]) =
12.7^+0.4_-0.6 and 13.3^+0.3_-0.4 for unobscured quasars (QSO-1s) and obscured
quasars (Obs-QSOs), respectively. The results for QSO-1s are in excellent
agreement with previous measurements for optically-selected quasars, while we
conclude that the Obs-QSOs are at least as strongly clustered as the QSO-1s. We
test for the effects of photometric redshift errors on the optically-faint
Obs-QSOs, and find that our method yields a robust lower limit on the
clustering; photo-z errors may cause us to underestimate the clustering
amplitude of the Obs-QSOs by at most ~20%. We compare our results to previous
studies, and speculate on physical implications of stronger clustering for
obscured quasars.
02/2011;
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[show abstract]
[hide abstract]
ABSTRACT: Tidal interactions between galaxies can trigger star formation, which contributes to the global star formation rate (SFR) density of the universe and could be a factor in the transformation of blue, star-forming galaxies to red, quiescent galaxies over cosmic time. We investigate tidally triggered star formation in isolated close galaxy pairs drawn from the Prism Multi-Object Survey (PRIMUS), a low-dispersion prism redshift survey that has measured ~120,000 robust galaxy redshifts over 9.1 deg2 out to z ~ 1. We select a sample of galaxies in isolated galaxy pairs at redshifts 0.25 ≤ z ≤ 0.75, with no other objects within a projected separation of 300 h –1 kpc and Δz/(1 + z) = 0.01, and compare them to a control sample of isolated galaxies to test for systematic differences in their rest-frame FUV – r and NUV – r colors as a proxy for relative specific star formation rates (SSFRs). We find that galaxies in rp ≤ 50 h –1 kpc pairs have bluer dust-corrected UV – r colors on average than the control galaxies by –0.134 ± 0.045 mag in FUV – r and –0.075 ± 0.038 mag in NUV – r, corresponding to an ~15%-20% increase in SSFR. This indicates an enhancement in SSFR due to tidal interactions. We also find that this relative enhancement is greater for a subset of rp ≤ 30 h –1 kpc pair galaxies, for which the average color offsets are –0.193 ± 0.065 mag in FUV – r and –0.159 ± 0.048 mag in NUV – r, corresponding to an ~25%-30% increase in SSFR. We test for evolution in the enhancement of tidally triggered star formation with redshift across our sample redshift range and find marginal evidence for a decrease in SSFR enhancement from 0.25 ≤ z ≤ 0.5 to 0.5 ≤ z ≤ 0.75. This indicates that a change in enhanced star formation triggered by tidal interactions in low-density environments is not a contributor to the decline in the global SFR density across this redshift range.
The Astrophysical Journal 01/2011; 728(2):119. · 6.02 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: We quantify the fraction of galaxies at moderate redshifts (0.1 < z < 0.5) that appear red-and-dead in the optical, but in fact contain obscured star formation detectable in the infrared (IR), with the PRIsm MUlti-object Survey (PRIMUS). PRIMUS has measured ~120,000 robust redshifts with a precision of σ z /(1 + z) ~ 0.5% over 9.1 deg2 of the sky to the depth of i ~ 23 (AB), up to redshift z ~ 1. We specifically targeted 6.7 deg2 fields with existing deep IR imaging from the Spitzer Space Telescope from the SWIRE and S-COSMOS surveys. We select in these fields an i-band flux-limited sample (i < 20 mag in the SWIRE fields and i < 21 mag in the S-COSMOS field) of 3310 red-sequence galaxies at 0.1 < z < 0.5 for which we can reliably classify obscured star-forming (SF) and quiescent galaxies using IR color. Our sample constitutes the largest galaxy sample at intermediate redshift to study obscured star formation on the red sequence, and we present the first quantitative analysis of the fraction of obscured SF galaxies as a function of luminosity. We find that on average, at L ~ L*, about 15% of red-sequence galaxies have IR colors consistent with SF galaxies. The percentage of obscured SF galaxies increases by ~8% per mag with decreasing luminosity from the highest luminosities to L ~ 0.2 L*. Our results suggest that a significant fraction of red-sequence galaxies have ongoing star formation and that galaxy evolution studies based on optical color therefore need to account for this complication.
The Astrophysical Journal 12/2010; 726(2):110. · 6.02 Impact Factor
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Wiphu Rujopakarn,
Daniel J. Eisenstein,
George H. Rieke,
Casey Papovich, Richard J. Cool,
John Moustakas,
Buell T. Jannuzi,
Christopher S. Kochanek,
Marcia J. Rieke,
Arjun Dey,
Peter Eisenhardt,
Steve S. Murray,
Michael J. I. Brown,
and Emeric Le Floc'h
[show abstract]
[hide abstract]
ABSTRACT: We present the 24 μm rest-frame luminosity function (LF) of star-forming galaxies in the redshift range 0.0 ≤ z ≤ 0.6 constructed from 4047 spectroscopic redshifts from the AGN and Galaxy Evolution Survey of 24 μm selected sources in the Boötes field of the NOAO Deep Wide-Field Survey. This sample provides the best available combination of large area (9 deg2), depth, and statistically complete spectroscopic observations, allowing us to probe the evolution of the 24 μm LF of galaxies at low and intermediate redshifts while minimizing the effects of cosmic variance. In order to use the observed 24 μm luminosity as a tracer for star formation, active galactic nuclei (AGNs) that could contribute significantly at 24 μm are identified and excluded from our star-forming galaxy sample based on their mid-IR spectral energy distributions or the detection of X-ray emission. Optical emission line diagnostics are considered for AGN identification, but we find that 24 μm emission from optically selected AGNs is usually from star-forming activity and therefore should not be excluded. The evolution of the 24 μm LF of star-forming galaxies for redshifts of z ≤ 0.65 is consistent with a pure luminosity evolution where the characteristic 24 μm luminosity evolves as (1 + z)3.8±0.3. We extend our evolutionary study to encompass 0.0 ≤ z ≤ 1.2 by combining our data with that of the Far-Infrared Deep Extragalactic Legacy Survey. Over this entire redshift range, the evolution of the characteristic 24 μm luminosity is described by a slightly shallower power law of (1 + z)3.4±0.2. We find a local star formation rate density of (1.09 ± 0.21) × 10–2 M ☉ yr–1 Mpc–3, and that it evolves as (1 + z)3.5±0.2 over 0.0 ≤ z ≤ 1.2. These estimates are in good agreement with the rates using optical and UV fluxes corrected for the effects of intrinsic extinction in the observed sources. This agreement confirms that star formation at z 1.2 is robustly traced by 24 μm observations and that it largely occurs in obscured regions of galaxies.
The Astrophysical Journal 07/2010; 718(2):1171. · 6.02 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: We have searched for active galactic nuclei (AGNs) in K+A galaxies, using multiwavelength imaging and spectroscopy in the Boötes field of the NOAO Deep Wide-Field Survey. The K+A galaxies, which have had their star formation rapidly truncated, are selected via their strong Balmer absorption lines and weak Hα emission. Our sample consists of 24 K+A galaxies selected from 6594 0.10 < z < 0.35 galaxies brighter than I = 20 with optical spectroscopy from the AGN and Galaxy Evolution Survey. Two thirds of the K+A galaxies are likely ongoing galaxy mergers, with nearby companion galaxies or tidal tails. Galaxy mergers may be responsible for the truncation of star formation, or we are observing the aftermath of merger triggered starbursts. As expected, the optical colors of K+A galaxies largely fall between blue galaxies with ongoing star formation and red passive galaxies. However, only 1% of the galaxies with colors between the red and blue populations are K+A galaxies, and we conclude that the truncation of star formation in K+A galaxies must have been unusually abrupt (100 Myr). We examined the AGN content of K+A galaxies with both optical emission-line ratios (BPT diagrams) and Chandra X-ray imaging. At least half of all K+A galaxies display the optical emission-line ratios of AGNs, and a third of MR < –22 K+A galaxies host AGNs with X-ray luminosities of ~1042 erg s–1. The faintest K+A galaxies do not show clear evidence for hosting AGNs, having emission-line ratios consistent with photoionization by massive stars and few X-ray detections. We speculate that two mechanisms may be responsible for the truncation of star formation in K+A galaxies, with AGN feedback only playing a role in MR –20.5 galaxies.
The Astrophysical Journal 08/2009; 703(1):150. · 6.02 Impact Factor
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Ryan C. Hickox,
Christine Jones,
William R. Forman,
Stephen S. Murray,
Christopher S. Kochanek,
Daniel Eisenstein,
Buell T. Jannuzi,
Arjun Dey,
Michael J. I. Brown,
Daniel Stern,
Peter R. Eisenhardt,
Varoujan Gorjian,
Mark Brodwin,
Ramesh Narayan, Richard J. Cool,
Almus Kenter,
Nelson Caldwell,
and Michael E. Anderson
[show abstract]
[hide abstract]
ABSTRACT: We explore the connection between different classes of active galactic nuclei (AGNs) and the evolution of their host galaxies, by deriving host galaxy properties, clustering, and Eddington ratios of AGNs selected in the radio, X-ray, and infrared (IR) wavebands. We study a sample of 585 AGNs at 0.25 < z < 0.8 using redshifts from the AGN and Galaxy Evolution Survey (AGES). We select AGNs with observations in the radio at 1.4 GHz from the Westerbork Synthesis Radio Telescope, X-rays from the Chandra XBoötes Survey, and mid-IR from the Spitzer IRAC Shallow Survey. The radio, X-ray, and IR AGN samples show only modest overlap, indicating that to the flux limits of the survey, they represent largely distinct classes of AGNs. We derive host galaxy colors and luminosities, as well as Eddington ratios, for obscured or optically faint AGNs. We also measure the two-point cross-correlation between AGNs and galaxies on scales of 0.3-10 h –1 Mpc, and derive typical dark matter halo masses. We find that: (1) radio AGNs are mainly found in luminous red sequence galaxies, are strongly clustered (with M halo ~ 3 × 1013 h –1 M ☉), and have very low Eddington ratios λ 10–3; (2) X-ray-selected AGNs are preferentially found in galaxies that lie in the "green valley" of color-magnitude space and are clustered similar to the typical AGES galaxies (M halo ~ 1013 h –1 M ☉), with 10–3 λ 1; (3) IR AGNs reside in slightly bluer, slightly less luminous galaxies than X-ray AGNs, are weakly clustered (M halo 1012 h –1 M ☉), and have λ>10–2. We interpret these results in terms of a simple model of AGN and galaxy evolution, whereby a "quasar" phase and the growth of the stellar bulge occurs when a galaxy's dark matter halo reaches a critical mass between ~1012 and 1013 M ☉. After this event, star formation ceases and AGN accretion shifts from radiatively efficient (optical- and IR-bright) to radiatively inefficient (optically faint, radio-bright) modes.
The Astrophysical Journal 04/2009; 696(1):891. · 6.02 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: We measure the evolution of the luminous red galaxy (LRG) luminosity function in the redshift range 0.1 < z < 0.9 using samples of galaxies from the Sloan Digital Sky Survey as well as new spectroscopy of high-redshift massive red galaxies. Our high-redshift sample of galaxies is largest spectroscopic sample of massive red galaxies at z ~ 0.9 collected to date and covers 7 deg2, minimizing the impact of large-scale structure on our results. We find that the LRG population has evolved little beyond the passive fading of its stellar populations since z ~ 0.9. Based on our luminosity function measurements and assuming a nonevolving Salpeter stellar initial mass function, we find that the most massive (L > 3L*) red galaxies have grown by less than 50% (at 99% confidence), since z = 0.9, in stark contrast to the factor of 2-4 growth observed in the L* red galaxy population over the same epoch. We also investigate the evolution of the average LRG spectrum since z ~ 0.9 and find the high-redshift composite to be well described as a passively evolving example of the composite galaxy observed at low redshift. From spectral fits to the composite spectra, we find at most 5% of the stellar mass in massive red galaxies may have formed within 1 Gyr of z = 0.9. While L* red galaxies are clearly assembled at z < 1, 3L* galaxies appear to be largely in place and evolve little beyond the passive evolution of their stellar populations over the last half of cosmic history.
The Astrophysical Journal 12/2008; 682(2):919. · 6.02 Impact Factor
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Morad Masjedi,
David W. Hogg, Richard J. Cool,
Daniel J. Eisenstein,
Michael R. Blanton,
Idit Zehavi,
Andreas A. Berlind,
Eric F. Bell,
Donald P. Schneider,
Michael S. Warren,
and Jon Brinkmann
[show abstract]
[hide abstract]
ABSTRACT: We present the small-scale (0.01 Mpc < r < 8 h-1 Mpc) projected correlation function wp(rp) and real-space correlation function ξ(r) of 24,520 luminous early-type galaxies from the Sloan Digital Sky Survey (SDSS) Luminous Red Galaxy (LRG) sample (0.16 < z < 0.36). "Fiber collision" incompleteness of the SDSS spectroscopic sample at scales smaller than 55'' prevents measurements of the correlation function for LRGs on scales smaller than ~0.3 Mpc by the usual methods. In this work, we cross-correlate the spectroscopic sample with the imaging sample, with a weighting scheme to account for the collisions, extensively tested against mock catalogs. We correct for photometric biases in the SDSS imaging of close galaxy pairs. We find that the correlation function ξ(r) is surprisingly close to a r-2 power law over more than 4 orders of magnitude in separation r. This result is too steep at small scales to be explained in current versions of the halo model for galaxy clustering. We infer an LRG-LRG merger rate of 0.6 × 104 Gyr-1 Gpc-3 for this sample. This result suggests that the LRG-LRG mergers are not the main mode of mass growth for LRGs at z < 0.36.
The Astrophysical Journal 12/2008; 644(1):54. · 6.02 Impact Factor
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Linhua Jiang,
Xiaohui Fan, Richard J. Cool,
Daniel J. Eisenstein,
Idit Zehavi,
Gordon T. Richards,
Ryan Scranton,
David Johnston,
Michael A. Strauss,
Donald P. Schneider,
and J. Brinkmann
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ABSTRACT: In this paper we present the first results of a deep spectroscopic survey of faint quasars in the Sloan Digital Sky Survey (SDSS) Southern Survey, a deep survey carried out by repeatedly imaging a 270 deg2 area. Quasar candidates were selected from the deep data with good completeness over 0 < z < 5 and 2-3 mag fainter than the SDSS main survey. Spectroscopic follow-up was carried out on the 6.5 m MMT with Hectospec. The preliminary sample of this SDSS faint quasar survey (SFQS) covers ~3.9 deg2, contains 414 quasars, and reaches g = 22.5. The overall selection efficiency is ~66% (~80% at g < 21.5); the efficiency in the most difficult redshift range (2 < z < 3) is better than 40%. We use the 1/Va method to derive a binned estimate of the quasar luminosity function (QLF) and model the QLF using maximum likelihood analysis. The best model fits confirm previous results showing that the QLF has steep slopes at the bright end and much flatter slopes (-1.25 at z 2.0 and -1.55 at z 2.0) at the faint end, indicating a break in the QLF slope. Using a luminosity-dependent density evolution model, we find that the quasar density at Mg < -22.5 peaks at z ~ 2, which is later in cosmic time than the peak of z ~ 2.5 found from surveys of more luminous objects. The SFQS QLF is consistent with the results of the 2dF QSO Redshift Survey, the SDSS, and the 2dF-SDSS LRG and QSO Survey, but probes fainter quasars. We plan to obtain more quasars from future observations and establish a complete faint quasar sample with more than 1000 objects over 10 deg2.
The Astronomical Journal 12/2007; 131(6):2788. · 4.03 Impact Factor
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Richard J. Cool,
Christopher S. Kochanek,
Daniel J. Eisenstein,
Daniel Stern,
Kate Brand,
Michael J. I. Brown,
Arjun Dey,
Peter R. Eisenhardt,
Xiaohui Fan,
Anthony H. Gonzalez,
Richard F. Green,
Buell T. Jannuzi,
Eric H. McKenzie,
George H. Rieke,
Marcia Rieke,
Baruch T. Soifer,
Hyron Spinrad,
and Richard J. Elston
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ABSTRACT: We present the discovery of three z > 5 quasars in the AGN and Galaxy Evolution Survey spectroscopic observations of the NOAO Deep Wide-Field Survey (NDWFS) Bootes Field. These quasars were selected as part of a larger Spitzer mid-infrared quasar sample, with no selection based on optical colors. The highest redshift object, NDWFS J142516.3+325409, at z = 5.85, is the lowest luminosity z > 5.8 quasar currently known. We compare mid-infrared techniques for identifying z > 5 quasars to more traditional optical techniques and show that mid-infrared colors allow for the selection of high-redshift quasars even at redshifts at which quasars lie near the optical stellar locus and at z > 7, where optical selection is impossible. Using the superb multiwavelength coverage available in the NDWFS Bootes field, we construct the spectral energy distributions (SEDs) of high-redshift quasars from observed BW band to 24 μm (rest-frame 600 Å-3.7 μm). We show that the three high-redshift quasars have quite similar SEDs, and the rest-frame composite SED of low-redshift quasars from the literature shows little evolution compared to our high-redshift objects. We compare the number of z > 5 quasars we have discovered to the expected number from published quasar luminosity functions. While analyses of the quasar luminosity function are tenuous based on only three objects, we find that a relatively steep luminosity function with Ψ ∝ L-3.2 provides the best agreement with the number of high-redshift quasars discovered in our survey.
The Astronomical Journal 12/2007; 132(2):823. · 4.03 Impact Factor
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ABSTRACT: In this paper, we present Sloan Digital Sky Survey (SDSS) photometry and spectroscopy in the fields of 24 gamma-ray bursts (GRBs) observed by Swift, including bursts localized by Swift, HETE-2, and INTEGRAL, after December 2004. After this bulk release, we plan to provide individual releases of similar data shortly after the localization of future bursts falling in the SDSS survey area. These data provide a solid basis for the astrometric and photometric calibration of follow-up afterglow searches and monitoring. Furthermore, the images provided with this release will allow observers to find transient objects up to a magnitude fainter than possible with Digitized Sky Survey image comparisons. Comment: Submitted in PASP. Data for GRB fields included in this release can be found at http://mizar.as.arizona.edu/grb/public. Updated with corrected object counts. Replaced with revised version
01/2006;
