461 research outputs found
WFMOS - Sounding the Dark Cosmos
Vast sound waves traveling through the relativistic plasma during the first
million years of the universe imprint a preferred scale in the density of
matter. We now have the ability to detect this characteristic fingerprint in
the clustering of galaxies at various redshifts and use it to measure the
acceleration of the expansion of the Universe. The Wide-Field Multi-Object
Spectrograph (WFMOS) would use this test to shed significant light on the true
nature of dark energy, the mysterious source of this cosmic acceleration. WFMOS
would also revolutionise studies of the kinematics of the Milky Way and provide
deep insights into the clustering of galaxies at redshifts up to z~4. In this
article we discuss the recent progress in large galaxy redshift surveys and
detail how WFMOS will help unravel the mystery of dark energy.Comment: 6 pages, pure pdf. An introduction to WFMOS and Baryon Acoustic
Oscillations for a general audienc
The Clustering of Luminous Red Galaxies in the Sloan Digital Sky Survey Imaging Data
We present the 3D real space clustering power spectrum of a sample of
\~600,000 luminous red galaxies (LRGs) measured by the Sloan Digital Sky Survey
(SDSS), using photometric redshifts. This sample of galaxies ranges from
redshift z=0.2 to 0.6 over 3,528 deg^2 of the sky, probing a volume of 1.5
(Gpc/h)^3, making it the largest volume ever used for galaxy clustering
measurements. We measure the angular clustering power spectrum in eight
redshift slices and combine these into a high precision 3D real space power
spectrum from k=0.005 (h/Mpc) to k=1 (h/Mpc). We detect power on gigaparsec
scales, beyond the turnover in the matter power spectrum, on scales
significantly larger than those accessible to current spectroscopic redshift
surveys. We also find evidence for baryonic oscillations, both in the power
spectrum, as well as in fits to the baryon density, at a 2.5 sigma confidence
level. The statistical power of these data to constrain cosmology is ~1.7 times
better than previous clustering analyses. Varying the matter density and baryon
fraction, we find \Omega_M = 0.30 \pm 0.03, and \Omega_b/\Omega_M = 0.18 \pm
0.04, The detection of baryonic oscillations also allows us to measure the
comoving distance to z=0.5; we find a best fit distance of 1.73 \pm 0.12 Gpc,
corresponding to a 6.5% error on the distance. These results demonstrate the
ability to make precise clustering measurements with photometric surveys
(abridged).Comment: 23 pages, 27 figures, submitted to MNRA
A Snapshot Survey for Gravitational Lenses Among z>=4.0 Quasars: I. The z>5.7 Sample
Over the last few years, the Sloan Digital Sky Survey (SDSS) has discovered
several hundred quasars with redshift between 4.0 and 6.4. Including the
effects of magnification bias, one expects a priori that an appreciable
fraction of these objects are gravitationally lensed. We have used the Advanced
Camera for Surveys on the Hubble Space Telescope to carry out a snapshot
imaging survey of high-redshift SDSS quasars to search for gravitationally
split lenses. This paper, the first in a series reporting the results of the
survey, describes snapshot observations of four quasars at z = 5.74, 5.82, 5.99
and 6.30, respectively. We find that none of these objects has a lensed
companion within 5 magnitudes with a separation larger than 0.3 arcseconds;
within 2.5 magnitudes, we can rule out companions within 0.1 arcseconds. Based
on the non-detection of strong lensing in these four systems, we constrain the
z~6 luminosity function to a slope of beta>-4.63 (3 sigma), assuming a break in
the quasar luminosity function at M_{1450}^*=-24.0. We discuss the implications
of this constraint on the ionizing background due to quasars in the early
universe. Given that these quasars are not highly magnified, estimates of the
masses of their central engines by the Eddington argument must be taken
seriously, possibly challenging models of black hole formation.Comment: 23 pages, 8 figures, 2 tables, submitted to A
Cosmological Constraints from the Clustering of the Sloan Digital Sky Survey DR7 Luminous Red Galaxies
We present the power spectrum of the reconstructed halo density field derived
from a sample of Luminous Red Galaxies (LRGs) from the Sloan Digital Sky Survey
Seventh Data Release (DR7). The halo power spectrum has a direct connection to
the underlying dark matter power for k <= 0.2 h/Mpc, well into the quasi-linear
regime. This enables us to use a factor of ~8 more modes in the cosmological
analysis than an analysis with kmax = 0.1 h/Mpc, as was adopted in the SDSS
team analysis of the DR4 LRG sample (Tegmark et al. 2006). The observed halo
power spectrum for 0.02 < k < 0.2 h/Mpc is well-fit by our model: chi^2 = 39.6
for 40 degrees of freedom for the best fit LCDM model. We find \Omega_m h^2 *
(n_s/0.96)^0.13 = 0.141^{+0.009}_{-0.012} for a power law primordial power
spectrum with spectral index n_s and \Omega_b h^2 = 0.02265 fixed, consistent
with CMB measurements. The halo power spectrum also constrains the ratio of the
comoving sound horizon at the baryon-drag epoch to an effective distance to
z=0.35: r_s/D_V(0.35) = 0.1097^{+0.0039}_{-0.0042}. Combining the halo power
spectrum measurement with the WMAP 5 year results, for the flat LCDM model we
find \Omega_m = 0.289 +/- 0.019 and H_0 = 69.4 +/- 1.6 km/s/Mpc. Allowing for
massive neutrinos in LCDM, we find \sum m_{\nu} < 0.62 eV at the 95% confidence
level. If we instead consider the effective number of relativistic species Neff
as a free parameter, we find Neff = 4.8^{+1.8}_{-1.7}. Combining also with the
Kowalski et al. (2008) supernova sample, we find \Omega_{tot} = 1.011 +/- 0.009
and w = -0.99 +/- 0.11 for an open cosmology with constant dark energy equation
of state w.Comment: 26 pages, 19 figures, submitted to MNRAS. The power spectrum and a
module to calculate the likelihoods is publicly available at
http://lambda.gsfc.nasa.gov/toolbox/lrgdr/ . v2 fixes abstract formatting
issu
Baryon Acoustic Oscillations in the Sloan Digital Sky Survey Data Release 7 Galaxy Sample
The spectroscopic Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7) galaxy
sample represents the final set of galaxies observed using the original SDSS
target selection criteria. We analyse the clustering of galaxies within this
sample, including both the Luminous Red Galaxy (LRG) and Main samples, and also
include the 2-degree Field Galaxy Redshift Survey (2dFGRS) data. Baryon
Acoustic Oscillations are observed in power spectra measured for different
slices in redshift; this allows us to constrain the distance--redshift relation
at multiple epochs. We achieve a distance measure at redshift z=0.275, of
r_s(z_d)/D_V(0.275)=0.1390+/-0.0037 (2.7% accuracy), where r_s(z_d) is the
comoving sound horizon at the baryon drag epoch,
D_V(z)=[(1+z)^2D_A^2cz/H(z)]^(1/3), D_A(z) is the angular diameter distance and
H(z) is the Hubble parameter. We find an almost independent constraint on the
ratio of distances D_V(0.35)/D_V(0.2)=1.736+/-0.065, which is consistent at the
1.1sigma level with the best fit Lambda-CDM model obtained when combining our
z=0.275 distance constraint with the WMAP 5-year data. The offset is similar to
that found in previous analyses of the SDSS DR5 sample, but the discrepancy is
now of lower significance, a change caused by a revised error analysis and a
change in the methodology adopted, as well as the addition of more data. Using
WMAP5 constraints on Omega_bh^2 and Omega_ch^2, and combining our BAO distance
measurements with those from the Union Supernova sample, places a tight
constraint on Omega_m=0.286+/-0.018 and H_0 = 68.2+/-2.2km/s/Mpc that is robust
to allowing curvature and non-Lambda dark energy. This result is independent of
the behaviour of dark energy at redshifts greater than those probed by the BAO
and supernova measurements. (abridged)Comment: 22 pages, 16 figures, minor changes to match version published in
MNRA
SDSS J115517.35+634622.0: A Newly Discovered Gravitationally Lensed Quasar
We report the discovery of SDSSJ115517.35+634622.0, a previously unknown
gravitationally lensed quasar. The lens system exhibits two images of a quasar, with an image separation of 1{\farcs}832 \pm 0.007 . Near-IR
imaging of the system reveals the presence of the lensing galaxy between the
two quasar images. Based on absorption features seen in the Sloan Digital Sky
Survey (SDSS) spectrum, we determine a lens galaxy redshift of .
The lens is rather unusual in that one of the quasar images is only
0{\farcs}22\pm0{\farcs}07 () from the center of the
lens galaxy and photometric modeling indicates that this image is significantly
brighter than predicted by a SIS model. This system was discovered in the
course of an ongoing search for strongly lensed quasars in the dataset from the
SDSS.Comment: 18 pages, 6 figures. Accepted for publication in A
The Sloan Digital Sky Survey Quasar Lens Search. II. Statistical lens sample from the third data release
We report the first results of our systematic search for strongly lensed quasars using the spectroscopically confirmed quasars in the Sloan Digital Sky Survey (SDSS). Among 46,420 quasars from the SDSS Data Release 3 (~4188 deg^2), we select a subsample of 22,683 quasars that are located at redshifts between 0.6 and 2.2 and are brighter than the Galactic extinction-corrected i-band magnitude of 19.1. We identify 220 lens candidates from the quasar subsample, for which we conduct extensive and systematic follow-up observations in optical and near-infrared wavebands, in order to construct a complete lensed quasar sample at image separations between 1" and 20" and flux ratios of faint to bright lensed images larger than 10^(−0.5). We construct a statistical sample of 11 lensed quasars. Ten of these are galaxy-scale lenses with small image separations (~ 1"-2") and one is a large separation (15") system which is produced by a massive cluster of galaxies, representing the first statistical sample of lensed quasars including both galaxy- and cluster-scale lenses. The Data Release 3 spectroscopic quasars contain an additional 11 lensed quasars outside the statistical sample
The clustering of Galaxies in the SDSS-III Baryon Oscillation Spectroscopic Survey : including covariance matrix errors
JP acknowledges support from the UK Science & Technology Facilities Council (STFC) through the consolidated grant ST/K0090X/1 and from the European Research Council through the ‘Starting Independent Research’ grant 202686, MDEPUGS. AGS acknowledges support from the Trans-regional Collaborative Research Centre TR33 ‘The Dark Universe’ of the German Research Foundation (DFG).We present improved methodology for including covariance matrices in the error budget of Baryon Oscillation Spectroscopic Survey (BOSS) galaxy clustering measurements, revisiting Data Release 9 (DR9) analyses, and describing a method that is used in DR10/11 analyses presented in companion papers. The precise analysis method adopted is becoming increasingly important, due to the precision that BOSS can now reach: even using as many as 600 mock catalogues to estimate covariance of two-point clustering measurements can still lead to an increase in the errors of ∼20 per cent, depending on how the cosmological parameters of interest are measured. In this paper, we extend previous work on this contribution to the error budget, deriving formulae for errors measured by integrating over the likelihood, and to the distribution of recovered best-fitting parameters fitting the simulations also used to estimate the covariance matrix. Both are situations that previous analyses of BOSS have considered. We apply the formulae derived to baryon acoustic oscillation (BAO) and redshift-space distortion (RSD) measurements from BOSS in our companion papers. To further aid these analyses, we consider the optimum number of bins to use for two-point measurements using the monopole power spectrum or correlation function for BAO, and the monopole and quadrupole moments of the correlation function for anisotropic-BAO and RSD measurements.Publisher PDFPeer reviewe
The SDSS-III Baryon Oscillation Spectroscopic Survey: Quasar Target Selection for Data Release Nine
The SDSS-III Baryon Oscillation Spectroscopic Survey (BOSS), a five-year
spectroscopic survey of 10,000 deg^2, achieved first light in late 2009. One of
the key goals of BOSS is to measure the signature of baryon acoustic
oscillations in the distribution of Ly-alpha absorption from the spectra of a
sample of ~150,000 z>2.2 quasars. Along with measuring the angular diameter
distance at z\approx2.5, BOSS will provide the first direct measurement of the
expansion rate of the Universe at z > 2. One of the biggest challenges in
achieving this goal is an efficient target selection algorithm for quasars over
2.2 < z < 3.5, where their colors overlap those of stars. During the first year
of the BOSS survey, quasar target selection methods were developed and tested
to meet the requirement of delivering at least 15 quasars deg^-2 in this
redshift range, out of 40 targets deg^-2. To achieve these surface densities,
the magnitude limit of the quasar targets was set at g <= 22.0 or r<=21.85.
While detection of the BAO signature in the Ly-alpha absorption in quasar
spectra does not require a uniform target selection, many other astrophysical
studies do. We therefore defined a uniformly-selected subsample of 20 targets
deg^-2, for which the selection efficiency is just over 50%. This "CORE"
subsample will be fixed for Years Two through Five of the survey. In this paper
we describe the evolution and implementation of the BOSS quasar target
selection algorithms during the first two years of BOSS operations. We analyze
the spectra obtained during the first year. 11,263 new z>2.2 quasars were
spectroscopically confirmed by BOSS. Our current algorithms select an average
of 15 z > 2.2 quasars deg^-2 from 40 targets deg^-2 using single-epoch SDSS
imaging. Multi-epoch optical data and data at other wavelengths can further
improve the efficiency and completeness of BOSS quasar target selection.
[Abridged]Comment: 33 pages, 26 figures, 12 tables and a whole bunch of quasars.
Submitted to Ap
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