-
[show abstract]
[hide abstract]
ABSTRACT: We describe ten strong lensing galaxy clusters of redshift 0.26-0.56 that
were found in the Sloan Digital Sky Survey. We present measurements of
richness, mass and velocity dispersion for the clusters. We find that in order
to use the mass-richness relation from Johnston et al. (2007), which was
established at mean redshift of 0.25, it is necessary to scale measured
richness values up by 1.47. We also present measurements of Einstein radius,
mass and velocity dispersion for the lensing systems. The Einstein radii are
all relatively small, between 5.4-13 arcseconds. Finally we consider if there
is evidence that our clusters are more concentrated than standard cosmology
would predict. We find that six of our clusters do not show evidence of
overconcentration, while four of our clusters do. We note a correlation between
overconcentration and mass, as the four clusters showing evidence of
overconcentration are all lower-mass clusters.
11/2012;
-
Cristina Furlanetto,
Basilio X. Santiago,
Martin Makler,
Eduardo S. Cypriano,
Gabriel B. Caminha,
Maria Elidaiana da Silva Pereira,
Angelo Fausti Neto,
Juan Estrada, Huan Lin,
Jiangang Hao,
Timothy A. McKay,
Luiz Nicolaci da Costa,
Marcio A. G. Maia
[show abstract]
[hide abstract]
ABSTRACT: We present the first results of the SOAR (Southern Astrophysical Research)
Gravitational Arc Survey (SOGRAS). The survey imaged 47 clusters in two
redshift intervals centered at $z=0.27$ and $z=0.55$, targeting the richest
clusters in each interval. Images were obtained in the $g'$, $r'$ and $i'$
bands using the SOAR Optical Imager (SOI), with a median seeing of 0.83, 0.76
and 0.71 arcsec, respectively, in these filters. Most of the survey clusters
are located within the Sloan Digital Sky Survey (SDSS) Stripe 82 region and all
of them are in the SDSS footprint. Photometric calibration was therefore
performed using SDSS stars located in our SOI fields. We reached for galaxies
in all fields the detection limits of $g \sim 23.5$, $r \sim 23$ and $i \sim
22.5$ for a signal-to-noise ratio (S/N) = 3. As a by-product of the image
processing, we generated a source catalogue with 19760 entries, the vast
majority of which are galaxies, where we list their positions, magnitudes and
shape parameters. We compared our galaxy shape measurements to those of local
galaxies and concluded that they were not strongly affected by seeing. From the
catalogue data, we are able to identify a red sequence of galaxies in most
clusters in the lower $z$ range. We found 16 gravitational arc candidates
around 8 clusters in our sample. They tend to be bluer than the central
galaxies in the lensing cluster. A preliminary analysis indicates that $\sim
10%$ of the clusters have arcs around them, with a possible indication of a
larger efficiency associated to the high-$z$ systems when compared to the
low-$z$ ones. Deeper follow-up images with Gemini strengthen the case for the
strong lensing nature of the candidates found in this survey.
10/2012;
-
[show abstract]
[hide abstract]
ABSTRACT: We use N-body-spectro-photometric simulations to investigate the impact of
incompleteness and incorrect redshifts in spectroscopic surveys to photometric
redshift training and calibration and the resulting effects on cosmological
parameter estimation from weak lensing shear-shear correlations. The photometry
of the simulations is modeled after the upcoming Dark Energy Survey and the
spectroscopy is based on a low/intermediate resolution spectrograph with
wavelength coverage of 5500{\AA} < {\lambda} < 9500{\AA}. The principal
systematic errors that such a spectroscopic follow-up encounters are
incompleteness (inability to obtain spectroscopic redshifts for certain
galaxies) and wrong redshifts. Encouragingly, we find that a neural
network-based approach can effectively describe the spectroscopic
incompleteness in terms of the galaxies' colors, so that the spectroscopic
selection can be applied to the photometric sample. Hence, we find that
spectroscopic incompleteness yields no appreciable biases to cosmology,
although the statistical constraints degrade somewhat because the photometric
survey has to be culled to match the spectroscopic selection. Unfortunately,
wrong redshifts have a more severe impact: the cosmological biases are
intolerable if more than a percent of the spectroscopic redshifts are
incorrect. Moreover, we find that incorrect redshifts can also substantially
degrade the accuracy of training set based photo-z estimators. The main problem
is the difficulty of obtaining redshifts, either spectroscopically or
photometrically, for objects at z > 1.3. We discuss several approaches for
reducing the cosmological biases, in particular finding that photo-z error
estimators can reduce biases appreciably.
07/2012;
-
Joseph J. Mohr,
Robert Armstrong,
Emmanuel Bertin,
Gregory E. Daues,
Shantanu Desai,
Michelle Gower,
Robert Gruendl,
William Hanlon,
Nikolay Kuropatkin, Huan Lin,
John Marriner,
Don Petravick,
Ignacio Sevilla,
Molly Swanson,
Todd Tomashek,
Douglas Tucker,
Brian Yanny,
the Dark Energy Survey Collaboration
[show abstract]
[hide abstract]
ABSTRACT: The Dark Energy Survey (DES) is a 5000 deg2 grizY survey reaching
characteristic photometric depths of 24th magnitude (10 sigma) and enabling
accurate photometry and morphology of objects ten times fainter than in SDSS.
Preparations for DES have included building a dedicated 3 deg2 CCD camera
(DECam), upgrading the existing CTIO Blanco 4m telescope and developing a new
high performance computing (HPC) enabled data management system (DESDM).
The DESDM system will be used for processing, calibrating and serving the DES
data. The total data volumes are high (~2PB), and so considerable effort has
gone into designing an automated processing and quality control system. Special
purpose image detrending and photometric calibration codes have been developed
to meet the data quality requirements, while survey astrometric calibration,
coaddition and cataloging rely on new extensions of the AstrOmatic codes which
now include tools for PSF modeling, PSF homogenization, PSF corrected model
fitting cataloging and joint model fitting across multiple input images.
The DESDM system has been deployed on dedicated development clusters and HPC
systems in the US and Germany. An extensive program of testing with small rapid
turn-around and larger campaign simulated datasets has been carried out. The
system has also been tested on large real datasets, including Blanco Cosmology
Survey data from the Mosaic2 camera. In Fall 2012 the DESDM system will be used
for DECam commissioning, and, thereafter, the system will go into full science
operations.
07/2012;
-
[show abstract]
[hide abstract]
ABSTRACT: The shapes of distant galaxies are sheared by intervening galaxy clusters. We examine this effect in Stripe 82, a 275 deg2 region observed multiple times in the Sloan Digital Sky Survey (SDSS) and co-added to achieve greater depth. We obtain a mass-richness calibration that is similar to other SDSS analyses, demonstrating that the co-addition process did not adversely affect the lensing signal. We also propose a new parameterization of the effect of tomography on the cluster lensing signal which does not require binning in redshift, and we show that using this parameterization we can detect tomography for stacked clusters at varying redshifts. Finally, due to the sensitivity of the tomographic detection to accurately marginalize over the effect of the cluster mass, we show that tomography at low redshift (where dependence on exact cosmological models is weak) can be used to constrain mass profiles in clusters.
The Astrophysical Journal 03/2012; 748(2):128. · 6.02 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We present and describe a catalog of galaxy photometric redshifts (photo-z) for the Sloan Digital Sky Survey (SDSS) Co-add Data. We use the artificial neural network (ANN) technique to calculate the photo-z and the nearest neighbor error method to estimate photo-z errors for ~13 million objects classified as galaxies in the co-add with r < 24.5. The photo-z and photo-z error estimators are trained and validated on a sample of ~83,000 galaxies that have SDSS photometry and spectroscopic redshifts measured by the SDSS Data Release 7 (DR7), the Canadian Network for Observational Cosmology Field Galaxy Survey, the Deep Extragalactic Evolutionary Probe Data Release 3, the VIsible imaging Multi-Object Spectrograph-Very Large Telescope Deep Survey, and the WiggleZ Dark Energy Survey. For the best ANN methods we have tried, we find that 68% of the galaxies in the validation set have a photo-z error smaller than σ68 = 0.031. After presenting our results and quality tests, we provide a short guide for users accessing the public data.
The Astrophysical Journal 02/2012; 747(1):59. · 6.02 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We present and describe a catalog of galaxy photometric redshifts (photo-z's)
for the Sloan Digital Sky Survey (SDSS) Coadd Data. We use the Artificial
Neural Network (ANN) technique to calculate photo-z's and the Nearest Neighbor
Error (NNE) method to estimate photo-z errors for $\sim$ 13 million objects
classified as galaxies in the coadd with $r < 24.5$. The photo-z and photo-z
error estimators are trained and validated on a sample of $\sim 83,000$
galaxies that have SDSS photometry and spectroscopic redshifts measured by the
SDSS Data Release 7 (DR7), the Canadian Network for Observational Cosmology
Field Galaxy Survey (CNOC2), the Deep Extragalactic Evolutionary Probe Data
Release 3(DEEP2 DR3), the VIsible imaging Multi-Object Spectrograph - Very
Large Telescope Deep Survey (VVDS) and the WiggleZ Dark Energy Survey. For the
best ANN methods we have tried, we find that 68% of the galaxies in the
validation set have a photo-z error smaller than $\sigma_{68} =0.031$. After
presenting our results and quality tests, we provide a short guide for users
accessing the public data.
11/2011;
-
[show abstract]
[hide abstract]
ABSTRACT: The shapes of distant galaxies are sheared by intervening galaxy clusters. We
examine this effect in Stripe 82, a 275 square degree region observed multiple
times in the Sloan Digital Sky Survey and coadded to achieve greater depth. We
obtain a mass-richness calibration that is similar to other SDSS analyses,
demonstrating that the coaddition process did not adversely affect the lensing
signal. We also propose a new parameterization of the effect of tomography on
the cluster lensing signal which does not require binning in redshift, and we
show that using this parameterization we can detect tomography for stacked
clusters at varying redshifts. Finally, due to the sensitivity of the
tomographic detection to accurately marginalizing over the effect of the
cluster mass, we show that tomography at low redshift (where dependence on
exact cosmological models is weak) can be used to constrain mass profiles in
clusters.
11/2011;
-
[show abstract]
[hide abstract]
ABSTRACT: Stripe 82 in the Sloan Digital Sky Survey was observed multiple times,
allowing deeper images to be constructed by coadding the data. Here we analyze
the ellipticities of background galaxies in this 275 square degree region,
searching for evidence of distortions due to cosmic shear. The E-mode is
detected in both real and Fourier space with $>5$-$\sigma$ significance on
degree scales, while the B-mode is consistent with zero as expected. The
amplitude of the signal constrains the combination of the matter density
$\Omega_m$ and fluctuation amplitude $\sigma_8$ to be $\Omega_m^{0.7}\sigma_8 =
0.252^{+0.032}_{-0.052}$.
11/2011;
-
James Annis,
Marcelle Soares-Santos,
Michael A. Strauss,
Andrew C. Becker,
Scott Dodelson,
Xiaohui Fan,
James E. Gunn,
Jiangang Hao,
Zeljko Ivezic,
Sebastian Jester,
Linhua Jiang,
David E. Johnston,
Jeffrey M. Kubo,
Hubert Lampeitl, Huan Lin,
Robert H. Lupton,
Gajus Miknaitis,
Hee-Jong Seo,
Melanie Simet,
Brian Yanny
[show abstract]
[hide abstract]
ABSTRACT: We present details of the construction and characterization of the coaddition
of the Sloan Digital Sky Survey Stripe 82 \ugriz\ imaging data. This survey
consists of 275 deg$^2$ of repeated scanning by the SDSS camera of $2.5\arcdeg$
of $\delta$ over $-50\arcdeg \le \alpha \le 60\arcdeg$ centered on the
Celestial Equator. Each piece of sky has $\sim 20$ runs contributing and thus
reaches $\sim2$ magnitudes fainter than the SDSS single pass data, i.e. to
$r\sim 23.5$ for galaxies. We discuss the image processing of the coaddition,
the modeling of the PSF, the calibration, and the production of standard SDSS
catalogs. The data have $r$-band median seeing of 1.1\arcsec, and are
calibrated to $\le 1%$. Star color-color, number counts, and psf size vs
modelled size plots show the modelling of the PSF is good enough for precision
5-band photometry. Structure in the psf-model vs magnitude plot show minor psf
mis-modelling that leads to a region where stars are being mis-classified as
galaxies, and this is verified using VVDS spectroscopy. As this is a wide area
deep survey there are a variety of uses for the data, including galactic
structure, photometric redshift computation, cluster finding and cross
wavelength measurements, weak lensing cluster mass calibrations, and cosmic
shear measurements.
11/2011;
-
[show abstract]
[hide abstract]
ABSTRACT: We present measurements of two types of cluster galaxy alignments based on a
volume limited and highly pure ($\ge$ 90%) sample of clusters from the GMBCG
catalog derived from SDSS DR7. We detect a clear BCG alignment (the alignment
of major axis of the BCG toward the distribution of cluster satellite
galaxies). We find that the BCG alignment signal becomes stronger as the
redshift and BCG absolute magnitude decrease, and becomes weaker as BCG stellar
mass decreases. No dependence of the BCG alignment on cluster richness is
found. We can detect a statistically significant ($\ge$ 3 sigma) satellite
alignment (the alignment of the major axes of the cluster satellite galaxies
toward the BCG) only when we use the isophotal fit position angles (PAs,
hereafter), and the satellite alignment depends on the apparent magnitudes
rather than the absolute magnitudes of the BCGs. This suggests the detected
satellite alignment based on isophotoal PAs from the SDSS pipeline is possibly
due to the contamination from the diffuse light of nearby BCGs. We caution that
this should not be simply interpreted as non-existence of the satellite
alignment, but rather that we cannot detect them with our current photometric
SDSS data. We perform our measurements on both SDSS $r$ band and $i$ band data,
but did not observe a passband dependence of the alignments.
03/2011;
-
Jeffrey M. Kubo,
Sahar S. Allam,
Emily Drabek, Huan Lin,
Douglas Tucker,
Elizabeth J. Buckley-Geer,
H. Thomas Diehl,
Marcelle Soares-Santos,
Jiangang Hao,
Matthew Wiesner,
Anderson West,
Donna Kubik,
James Annis,
and Joshua A. Frieman
[show abstract]
[hide abstract]
ABSTRACT: We report the discovery of seven new, very bright gravitational lens systems from our ongoing gravitational lens search, the Sloan Bright Arcs Survey (SBAS). Two of the systems are confirmed to have high source redshifts z = 2.19 and z = 2.94. Three other systems lie at intermediate redshift with z = 1.33, 1.82, 1.93 and two systems are at low redshift z = 0.66, 0.86. The lensed source galaxies in all of these systems are bright, with i-band magnitudes ranging from 19.73 to 22.06. We present the spectrum of each of the source galaxies in these systems along with estimates of the Einstein radius for each system. The foreground lens in most systems is identified by a red sequence based cluster finder as a galaxy group; one system is identified as a moderately rich cluster. In total, SBAS has now discovered 19 strong lens systems in the SDSS imaging data, 8 of which are among the highest surface brightness z 2-3 galaxies known.
The Astrophysical Journal Letters 11/2010; 724(2):L137. · 5.53 Impact Factor
-
Jiangang Hao,
Juan Estrada,
Herman Cease,
H. Thomas Diehl,
Brenna L. Flaugher,
Donna Kubik,
Keivin Kuk,
Nickolai Kuropatkine, Huan Lin,
Jorge Montes,
Vic Scarpine,
Ken Schultz,
William Wester for the DES collaboration
[show abstract]
[hide abstract]
ABSTRACT: Large mosaic multiCCD camera is the key instrument for modern digital sky survey. DECam is an extremely red sensitive 520 Megapixel camera designed for the incoming Dark Energy Survey (DES). It is consist of sixty two 4k$\times$2k and twelve 2k x 2k 250-micron thick fully-depleted CCDs, with a focal plane of 44 cm in diameter and a field of view of 2.2 square degree. It will be attached to the Blanco 4-meter telescope at CTIO. The DES will cover 5000 square-degrees of the southern galactic cap in 5 color bands (g, r, i, z, Y) in 5 years starting from 2011. To achieve the science goal of constraining the Dark Energy evolution, stringent requirements are laid down for the design of DECam. Among them, the flatness of the focal plane needs to be controlled within a 60-micron envelope in order to achieve the specified PSF variation limit. It is very challenging to measure the flatness of the focal plane to such precision when it is placed in a high vacuum dewar at 173 K. We developed two image based techniques to measure the flatness of the focal plane. By imaging a regular grid of dots on the focal plane, the CCD offset along the optical axis is converted to the variation the grid spacings at different positions on the focal plane. After extracting the patterns and comparing the change in spacings, we can measure the flatness to high precision. In method 1, the regular dots are kept in high sub micron precision and cover the whole focal plane. In method 2, no high precision for the grid is required. Instead, we use a precise XY stage moves the pattern across the whole focal plane and comparing the variations of the spacing when it is imaged by different CCDs. Simulation and real measurements show that the two methods work very well for our purpose, and are in good agreement with the direct optical measurements. Comment: Presented at SPIE Conference,Ground-based and Airborne Instrumentation for Astronomy III, San Diego, 2010
10/2010;
-
[show abstract]
[hide abstract]
ABSTRACT: We present low-resolution, rest-frame ~ 5 - 12 micron Spitzer/IRS spectra of two lensed z ~ 2 UV-bright star-forming galaxies, SDSS J120602.09+514229.5 and SDSS J090122.37+181432.3. Using the magnification boost from lensing, we are able to study the physical properties of these objects in greater detail than is possible for unlensed systems. In both targets, we detect strong PAH emission at 6.2, 7.7, and 11.3 microns, indicating the presence of vigorous star formation. For J1206, we find a steeply rising continuum and significant [S IV] emission, suggesting that a moderately hard radiation field is powering continuum emission from small dust grains. The strength of the [S IV] emission also implies a sub-solar metallicity of ~ 0.5 Z_{Sun}, confirming published rest-frame optical measurements. In J0901, the PAH lines have large rest-frame equivalent widths (> 1 micron) and the continuum rises slowly with wavelength, suggesting that any AGN contribution to L_{IR} is insignificant, in contrast to the implications of optical emission-line diagnostics. Using [O III] line flux as a proxy for AGN strength, we estimate that the AGN in J0901 provides only a small fraction of its mid-infrared continuum flux. By combining the detection of [Ar II] with an upper limit on [Ar III] emission, we infer a metallicity of > 1.3 Z_{Sun}. This work highlights the importance of combining rest-frame optical and mid-IR spectroscopy in order to understand the detailed properties of star-forming galaxies at high redshift. Comment: 20 pages, 3 figures, 2 tables. ApJ accepted
The Astrophysical Journal 09/2010; · 6.02 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We report the discovery of four very bright, strongly lensed galaxies found via systematic searches for arcs in Sloan Digital Sky Survey Data Release 5 and 6. These were followed up with spectroscopy and imaging data from the Astrophysical Research Consortium 3.5 m telescope at Apache Point Observatory and found to have redshift z > 2.0. With isophotal magnitudes r = 19.2-20.4 and 3'' diameter magnitudes r = 20.0-20.6, these systems are some of the brightest and highest surface brightness lensed galaxies known in this redshift range. In addition to the magnitudes and redshifts, we present estimates of the Einstein radii, which range from 50 to 127, and use those to derive the enclosed masses of the lensing galaxies.
The Astrophysical Journal 11/2009; 707(1):686. · 6.02 Impact Factor
-
Erin S. Sheldon,
David E. Johnston,
Ryan Scranton,
Benjamin P. Koester,
Timothy A. McKay,
Hiroaki Oyaizu,
Carlos Cunha,
Marcos Lima, Huan Lin,
Joshua A. Frieman,
Risa H. Wechsler,
James Annis,
Rachel Mandelbaum,
Neta A. Bahcall,
and Masataka Fukugita
[show abstract]
[hide abstract]
ABSTRACT: This is the first in a series of papers on the weak lensing effect caused by clusters of galaxies in Sloan Digital Sky Survey. The photometrically selected cluster sample, known as MaxBCG, includes ~130,000 objects between redshift 0.1 and 0.3, ranging in size from small groups to massive clusters. We split the clusters into bins of richness and luminosity and stack the surface density contrast to produce mean radial profiles. The mean profiles are detected over a range of scales, from the inner halo (25 kpc h –1) well into the surrounding large-scale structure (30 Mpc h –1), with a significance of 15 to 20 in each bin. The signal over this large range of scales is best interpreted in terms of the cluster-mass cross-correlation function. We pay careful attention to sources of systematic error, correcting for them where possible. The resulting signals are calibrated to the ~10% level, with the dominant remaining uncertainty being the redshift distribution of the background sources. We find that the profiles scale strongly with richness and luminosity. We find that the signal within a given richness bin depends upon luminosity, suggesting that luminosity is more closely correlated with mass than galaxy counts. We split the samples by redshift but detect no significant evolution. The profiles are not well described by power laws. In a subsequent series of papers, we invert the profiles to three-dimensional mass profiles, show that they are well fit by a halo model description, measure mass-to-light ratios, and provide a cosmological interpretation.
The Astrophysical Journal 09/2009; 703(2):2217. · 6.02 Impact Factor
-
Jeffrey M. Kubo,
James Annis,
Frances M. Hardin,
Donna Kubik,
Kelsey Lawhorn, Huan Lin,
Liana Nicklaus,
Dylan Nelson,
Ribamar R. R. Reis,
Hee-Jong Seo,
Marcelle Soares-Santos,
Albert Stebbins,
and Tony Yunker
[show abstract]
[hide abstract]
ABSTRACT: We describe and present initial results of a weak lensing survey of nearby (z 0.1) galaxy clusters in the Sloan Digital Sky Survey (SDSS). In this first study, galaxy clusters are selected from the SDSS spectroscopic galaxy cluster catalogs of Miller et al. and Berlind et al. We report a total of seven individual low-redshift cluster weak lensing measurements that include A2048, A1767, A2244, A1066, A2199, and two clusters specifically identified with the C4 algorithm. Our program of weak lensing of nearby galaxy clusters in the SDSS will eventually reach ~200 clusters, making it the largest weak lensing survey of individual galaxy clusters to date.
The Astrophysical Journal 08/2009; 702(2):L110. · 6.02 Impact Factor
-
Huan Lin,
Elizabeth Buckley-Geer,
Sahar S. Allam,
Douglas L. Tucker,
H. Thomas Diehl,
Donna Kubik,
Jeffrey M. Kubo,
James Annis,
Joshua A. Frieman,
Masamune Oguri,
and Naohisa Inada
[show abstract]
[hide abstract]
ABSTRACT: We report on the discovery of a very bright z = 2.00 star-forming galaxy that is strongly lensed by a foreground z = 0.422 luminous red galaxy (LRG), SDSS J120602.09+514229.5. This system, nicknamed the "Clone," was found in a systematic search for bright arcs lensed by LRGs and brightest cluster galaxies in the Sloan Digital Sky Survey Data Release 5 sample. Follow-up observations on the Subaru 8.2 m telescope on Mauna Kea and the Astrophysical Research Consortium 3.5 m telescope at Apache Point Observatory confirmed the lensing nature of this system. A simple lens model for the system, assuming a singular isothermal ellipsoid mass distribution, yields an Einstein radius of θEin = 3.82 ± 003 or 14.8 ± 0.1 h –1 kpc at the lens redshift. The total projected mass enclosed within the Einstein radius is 2.10 ± 0.03 × 1012 h –1 M ☉, and the magnification factor for the source galaxy is 27 ± 1. Combining the lens model with our gVriz photometry, we find a (unlensed) star formation rate (SFR) for the source galaxy of 32 h –1 M ☉ yr–1, adopting a fiducial constant SFR model with an age of 100 Myr and E(B – V) = 0.25. With an apparent magnitude of r = 19.8, this system is among the very brightest lensed z ≥ 2 galaxies, and provides an excellent opportunity to pursue detailed studies of the physical properties of an individual high-redshift star-forming galaxy.
The Astrophysical Journal 06/2009; 699(2):1242. · 6.02 Impact Factor
-
Linhua Jiang,
Xiaohui Fan,
Fuyan Bian,
James Annis,
Kuenley Chiu,
Sebastian Jester, Huan Lin,
Robert H. Lupton,
Gordon T. Richards,
Michael A. Strauss,
Viktor Malanushenko,
Elena Malanushenko,
and Donald P. Schneider
[show abstract]
[hide abstract]
ABSTRACT: We present the discovery of six new quasars at z ~ 6 selected from the Sloan Digital Sky Survey (SDSS) southern survey, a deep imaging survey obtained by repeatedly scanning a stripe along the celestial equator. The six quasars are about 2 mag fainter than the luminous z ~ 6 quasars found in the SDSS main survey and 1 mag fainter than the quasars reported in Paper I. Four of them comprise a complete flux-limited sample at 21 < z AB < 21.8 over an effective area of 195 deg2. The other two quasars are fainter than z AB = 22 and are not part of the complete sample. The quasar luminosity function at z ~ 6 is well described as a single power law Φ(L 1450) L β 1450 over the luminosity range –28 < M 1450 < –25. The best-fitting slope β varies from –2.6 to –3.1, depending on the quasar samples used, with a statistical error of 0.3-0.4. About 40% of the quasars discovered in the SDSS southern survey have very narrow Lyα emission lines, which may indicate small black hole masses and high Eddington luminosity ratios, and therefore short black hole growth timescales for these faint quasars at early epochs.
The Astronomical Journal 06/2009; 138(1):305. · 4.03 Impact Factor
-
Linhua Jiang,
Xiaohui Fan,
Fuyan Bian,
James Annis,
Kuenley Chiu,
Sebastian Jester, Huan Lin,
Robert H. Lupton,
Gordon T. Richards,
Michael A. Strauss,
Viktor Malanushenko,
Elena Malanushenko,
Donald P. Schneider
[show abstract]
[hide abstract]
ABSTRACT: We present the discovery of six new quasars at z~6 selected from the Sloan Digital Sky Survey (SDSS) southern survey, a deep imaging survey obtained by repeatedly scanning a stripe along the celestial equator. The six quasars are about two magnitudes fainter than the luminous z~6 quasars found in the SDSS main survey and one magnitude fainter than the quasars reported in Paper I (Jiang et al. 2008). Four of them comprise a complete flux-limited sample at 21<z_AB<21.8 over an effective area of 195 deg^2. The other two quasars are fainter than z_AB=22 and are not part of the complete sample. The quasar luminosity function at z~6 is well described as a single power law \Phi(L_{1450}) \propto L_{1450}^{\beta} over the luminosity range -28<M_{1450}<-25. The best-fitting slope \beta varies from -2.6 to -3.1, depending on the quasar samples used, with a statistical error of 0.3-0.4. About 40% of the quasars discovered in the SDSS southern survey have very narrow Lya emission lines, which may indicate small black hole masses and high Eddington luminosity ratios, and therefore short black hole growth time scales for these faint quasars at early epochs. Comment: Accepted for publication in AJ
05/2009;
