1,101 research outputs found
Photometric redshift requirements for lens galaxies in galaxy-galaxy lensing analyses
Weak gravitational lensing is a valuable probe of galaxy formation and
cosmology. Here we quantify the effects of using photometric redshifts
(photo-z) in galaxy-galaxy lensing, for both sources and lenses, both for the
immediate goal of using galaxies with photo-z as lenses in the Sloan Digital
Sky Survey (SDSS) and as a demonstration of methodology for large, upcoming
weak lensing surveys that will by necessity be dominated by lens samples with
photo-z. We calculate the bias in the lensing mass calibration as well as
consequences for absolute magnitude (i.e., k-corrections) and stellar mass
estimates, for a large sample of SDSS Data Release 8 (DR8) galaxies. The
redshifts are obtained with the template based photo-z code ZEBRA on the SDSS
DR8 ugriz photometry. We assemble and characterise the calibration samples (~9k
spectroscopic redshifts from four surveys) to obtain photometric redshift
errors and lensing biases corresponding to our full SDSS DR8 lens and source
catalogues. Our tests of the calibration sample also highlight the impact of
observing conditions in the imaging survey when the spectroscopic calibration
covers a small fraction of its footprint; atypical imaging conditions in
calibration fields can lead to incorrect conclusions regarding the photo-z of
the full survey. For the SDSS DR8 catalogue, we find sigma_z/(1+z)=0.096 and
0.113 for the lens and source catalogues, with flux limits of r=21 and r=21.8,
respectively. We also explore the systematic uncertainty in the lensing signal
calibration when using source photo-z, and both lens and source photo-z; given
the size of existing training samples, we can constrain the lensing signal
calibration (and therefore the normalization of the surface mass density) to
within 2 and 4 per cent, respectively. [ABRIDGED]Comment: 26 pages, 28 figures, minor changes, accepted for publication in
MNRA
Photometric redshift requirements for lens galaxies in galaxy-galaxy lensing analyses
Weak gravitational lensing is a valuable probe of galaxy formation and cosmology. Here we quantify the effects of using photometric redshifts (photo-z) in galaxy-galaxy lensing, for both sources and lenses, both for the immediate goal of using galaxies with photo-z as lenses in the Sloan Digital Sky Survey (SDSS) and as a demonstration of methodology for large, upcoming weak lensing surveys that will by necessity be dominated by lens samples with photo-z. We calculate the bias in the lensing mass calibration as well as consequences for absolute magnitude (i.e. k-corrections) and stellar mass estimates for a large sample of SDSS Data Release 8 (DR8) galaxies. The redshifts are obtained with the template-based photo-z code zebra on the SDSS DR8 ugriz photometry. We assemble and characterize the calibration samples (∼9000 spectroscopic redshifts from four surveys) to obtain photometric redshift errors and lensing biases corresponding to our full SDSS DR8 lens and source catalogues. Our tests of the calibration sample also highlight the impact of observing conditions in the imaging survey when the spectroscopic calibration covers a small fraction of its footprint; atypical imaging conditions in calibration fields can lead to incorrect conclusions regarding the photo-z of the full survey. For the SDSS DR8 catalogue, we find σΔz/(1+z)= 0.096 and 0.113 for the lens and source catalogues, with flux limits of r= 21 and 21.8, respectively. The photo-z bias and scatter is a function of photo-z and template types, which we exploit to apply photo-z quality cuts. By using photo-z rather than spectroscopy for lenses, dim blue galaxies and L* galaxies up to z∼ 0.4 can be used as lenses, thus expanding into unexplored areas of parameter space. We also explore the systematic uncertainty in the lensing signal calibration when using source photo-z, and both lens and source photo-z; given the size of existing training samples, we can constrain the lensing signal calibration (and therefore the normalization of the surface mass density) to within 2 and 4 per cent, respectivel
PRIMUS: The Effect of Physical Scale on the Luminosity-Dependence of Galaxy Clustering via Cross-Correlations
We report small-scale clustering measurements from the PRIMUS spectroscopic
redshift survey as a function of color and luminosity. We measure the
real-space cross-correlations between 62,106 primary galaxies with PRIMUS
redshifts and a tracer population of 545,000 photometric galaxies over
redshifts from z=0.2 to z=1. We separately fit a power-law model in redshift
and luminosity to each of three independent color-selected samples of galaxies.
We report clustering amplitudes at fiducial values of z=0.5 and L=1.5 L*. The
clustering of the red galaxies is ~3 times as strong as that of the blue
galaxies and ~1.5 as strong as that of the green galaxies. We also find that
the luminosity dependence of the clustering is strongly dependent on physical
scale, with greater luminosity dependence being found between r=0.0625 Mpc/h
and r=0.25 Mpc/h, compared to the r=0.5 Mpc/h to r=2 Mpc/h range. Moreover,
over a range of two orders of magnitude in luminosity, a single power-law fit
to the luminosity dependence is not sufficient to explain the increase in
clustering at both the bright and faint ends at the smaller scales. We argue
that luminosity-dependent clustering at small scales is a necessary component
of galaxy-halo occupation models for blue, star-forming galaxies as well as for
red, quenched galaxies.Comment: 13 pages, 6 figures, 5 tables; published in ApJ (revised to match
published version
PRIMUS: An observationally motivated model to connect the evolution of the AGN and galaxy populations out to z~1
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. 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 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, a steep power-law tail to super-Eddington
ratios with slope gamma_2 = -2.1 +0.3 -0.5, and a scatter of 0.38 dex in the
scaling between black hole and host stellar mass. 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 due to the shape
of the galaxy stellar mass function rather than a preference for AGN activity
at a particular stellar mass. Luminous AGNs may be a severely skewed population
with elevated black hole masses relative to their host galaxies and in rare
phases of rapid accretion.Comment: 11 pages, 5 figures, emulateapj format, updated to match version
accepted for publication in Ap
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
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