1,002 research outputs found
The Mid-IR and X-ray Selected QSO Luminosity Function
We present the J-band luminosity function of 1838 mid-infrared and X-ray
selected AGNs in the redshift range 0<z<5.85. These luminosity functions are
constructed by combining the deep multi-wavelength broad-band observations from
the UV to the mid-IR of the NDWFS Bootes field with the X-ray observations of
the XBootes survey and the spectroscopic observations of the same field by
AGES. Our sample is primarily composed of IRAC-selected AGNs, targeted using
modifications of the Stern et al.(2005) criteria, complemented by MIPS 24
microns and X-ray selected AGNs to alleviate the biases of IRAC mid-IR
selection against z~4.5 quasars and AGNs faint with respect to their hosts.
This sample provides an accurate link between low and high redshift AGN
luminosity functions and does not suffer from the usual incompleteness of
optical samples at z~3. We find that the space density of the brightest quasars
strongly decreases from z=3 to z=0, while the space density of faint quasars is
at least flat, and possibly increasing, over the same redshift range. At z>3 we
observe a decrease in the space density of quasars of all brightnesses. We
model the luminosity function by a double power-law and find that its evolution
cannot be described by either pure luminosity or pure density evolution, but
must be a combination of both. Our best-fit model has bright and faint
power-law indices consistent with the low redshift measurements based on the
2QZ and 2SLAQ surveys and it generally agrees with the number of bright quasars
predicted by other LFs at all redshifts. If we construct the QSO luminosity
function using only the IRAC-selected AGNs, we find that the biases inherent to
this selection method significantly modify the behavior of phi*(z) only for z<1
and have no significant impact upon the characteristic magnitude M*_J(z).Comment: Corrected minor typo in equations (4) and (6). Accepted for
publication in The Astrophysical Journal. 56 pages + 6 tables + 16 figure
PRIMUS + DEEP2: Clustering of X-ray, Radio and IR-AGN at z~0.7
We measure the clustering of X-ray, radio, and mid-IR-selected active
galactic nuclei (AGN) at 0.2 < z < 1.2 using multi-wavelength imaging and
spectroscopic redshifts from the PRIMUS and DEEP2 redshift surveys, covering 7
separate fields spanning ~10 square degrees. Using the cross-correlation of AGN
with dense galaxy samples, we measure the clustering scale length and slope, as
well as the bias, of AGN selected at different wavelengths. Similar to previous
studies, we find that X-ray and radio AGN are more clustered than
mid-IR-selected AGN. We further compare the clustering of each AGN sample with
matched galaxy samples designed to have the same stellar mass, star formation
rate, and redshift distributions as the AGN host galaxies and find no
significant differences between their clustering properties. The observed
differences in the clustering of AGN selected at different wavelengths can
therefore be explained by the clustering differences of their host populations,
which have different distributions in both stellar mass and star formation
rate. Selection biases inherent in AGN selection, therefore, determine the
clustering of observed AGN samples. We further find no significant difference
between the clustering of obscured and unobscured AGN, using IRAC or WISE
colors or X-ray hardness ratio.Comment: Accepted to ApJ. 23 emulateapj pages, 15 figures, 4 table
Quasars in the COSMOS Field
We obtained medium-resolution spectra of 336 quasar candidates in the COSMOS
HST/Treasury field using the MMT 6.5-meter telescope and the Hectospec
multi-object spectrograph. Candidates were drawn from the Sloan Digital Sky
Survey (SDSS) DR1 catalog using quasar flags set by the SDSS multi-color quasar
target selection algorithm. In this paper we present our discovery spectra from
1.39 square degrees (69.5% of the COSMOS field) and a discussion of the
selection method and yields. We confirmed 95 quasars, including at least 2
BALs; 80 of these are new quasars that do not appear in previous quasar
confirmation follow-up studies. The candidates additionally included 184
compact emission-line galaxies, a third of which are likely Type 2 AGN, and 12
stars. The quasars span a range in magnitude of 18.3<g<22.5 and a range in
redshift of 0.2<z<2.3. Our results are consistent with a lower limit quasar
surface density from SDSS color selection of 102 per square degree down to
g=22.5 over the entire COSMOS field. This work is the first step toward the
eventual goal of setting up a grid of quasar absorption line probes of the 2
square degree field, and of conducting a complete census of supermassive black
holes in this well-studied survey region. The total quasar count at the
conclusion of this study is 139, making COSMOS one of the most densely-sampled
regions of sky where a grid of quasar sightlines can be used to probe the
intervening volume.Comment: Accepted for publication in ApJ; emulateapj style; 25 pages, 13
figures, 4 table
Deep Photometry of the Globular Cluster M5: Distance Estimates from White Dwarf and Main Sequence Stars
We present deep VI photometry of stars in the globular cluster M5 (NGC 5904)
based on images taken with the Hubble Space Telescope. The resulting
color-magnitude diagram reaches below V ~ 27 mag, revealing the upper 2-3
magnitudes of the white dwarf cooling sequence, and main sequence stars eight
magnitudes and more below the turn-off. We fit the main sequence to subdwarfs
of known parallax to obtain a true distance modulus of (m-M)_0 = 14.45 +/- 0.11
mag. A second distance estimate based on fitting the cluster white dwarf
sequence to field white dwarfs with known parallax yielded (m-M)_0 = 14.67 +/-
0.18 mag. We couple our distance estimates with extensive photometry of the
cluster's RR Lyrae variables to provide a calibration of the RR Lyrae absolute
magnitude yielding M_V(RR) = 0.42 +/- 0.10 mag at [Fe/H] = -1.11 dex. We
provide another luminosity calibration in the form of reddening-free Wasenheit
functions. Comparison of our calibrations with predictions based on recent
models combining stellar evolution and pulsation theories shows encouraging
agreement. (Abridged)Comment: AASTeX, 29 pages including 5 figures. Complete photometry data and
FITS-format images are available at
http://physics.bgsu.edu/~layden/ASTRO/PUBL/published.html . Accepted for
publication in the Astrophysical Journal, 2005 October 20. Replaced errant
wording in last sentence of paragraph 4 of conclusion
A MMT/Hectospec Redshift Survey of 24 Micron Sources in the Spitzer First Look Survey
We present a spectroscopic survey using the MMT/Hectospec fiber spectrograph
of 24 micron sources selected with the Spitzer Space Telescope in the Spitzer
First Look Survey. We report 1296 new redshifts for 24 micron sources,
including 599 with f(24micron) > 1 mJy. Combined with 291 additional redshifts
for sources from the Sloan Digital Sky Survey (SDSS), our observing program was
highly efficient and is ~90% complete for i' 1 mJy,
and is 35% complete for i' < 20.5 mag and 0.3 mJy < f(24micron) < 1 mJy. Our
Hectospec survey includes 1078 and 168 objects spectroscopically classified as
galaxies and QSOs, respectively. Combining the Hectospec and SDSS samples, we
find 24 micron-selected galaxies to z < 0.98 and QSOs to z < 3.6, with mean
redshifts of = 0.27 and =1.1. As part of this publication, we
include the redshift catalogs and the reduced spectra; these are also available
online (http://mips.as.arizona.edu/~papovich/fls) and through the NASA/IPAC
Infrared Science Archive (http://irsa.ipac.caltech.edu).Comment: Accepted for publication in the Astronomical Journal, AASTEX format,
23 pages, 7 figures (some in color). This replacement is the accepted
version, and includes minor changes from previous version. Data tables and
spectra available at http://mips.as.arizona.edu/~papovich/fls or at
http://irsa.ipac.caltech.ed
PRIMUS: Galaxy Clustering as a Function of Luminosity and Color at 0.2<z<1
We present measurements of the luminosity and color-dependence of galaxy
clustering at 0.2<z<1.0 in the PRIsm MUlti-object Survey (PRIMUS). We quantify
the clustering with the redshift-space and projected two-point correlation
functions, xi(rp,pi) and wp(rp), using volume-limited samples constructed from
a parent sample of over 130,000 galaxies with robust redshifts in seven
independent fields covering 9 sq. deg. of sky. We quantify how the
scale-dependent clustering amplitude increases with increasing luminosity and
redder color, with relatively small errors over large volumes. We find that red
galaxies have stronger small-scale (0.1<rp<1 Mpc/h) clustering and steeper
correlation functions compared to blue galaxies, as well as a strong color
dependent clustering within the red sequence alone. We interpret our measured
clustering trends in terms of galaxy bias and obtain values between
b_gal=0.9-2.5, quantifying how galaxies are biased tracers of dark matter
depending on their luminosity and color. We also interpret the color dependence
with mock catalogs, and find that the clustering of blue galaxies is nearly
constant with color, while redder galaxies have stronger clustering in the
one-halo term due to a higher satellite galaxy fraction. In addition, we
measure the evolution of the clustering strength and bias, and we do not detect
statistically significant departures from passive evolution. We argue that the
luminosity- and color-environment (or halo mass) relations of galaxies have not
significantly evolved since z=1. Finally, using jackknife subsampling methods,
we find that sampling fluctuations are important and that the COSMOS field is
generally an outlier, due to having more overdense structures than other
fields; we find that 'cosmic variance' can be a significant source of
uncertainty for high-redshift clustering measurements.Comment: 22 pages, 21 figures, matches version published in Ap
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