1,427 research outputs found
Precision Cosmology from the Lyman-alpha Forest: Power Spectrum and Bispectrum
We investigate the promise of the Ly-alpha forest for high precision
cosmology in the era of the Sloan Digital Sky Survey using low order N-point
statistics. We show that with the existing data one can determine the
amplitude, slope and curvature of the slope of the matter power spectrum with a
few percent precision. Higher order statistics such as the bispectrum provide
independent information that can confirm and improve upon the statistical
precision from the power spectrum alone. The achievable precision is comparable
to that from the cosmic microwave background with upcoming satellites, and
complements it by measuring the power spectrum amplitude and shape at smaller
scales. Since the data cover the redshift range 2<z<4, one can also extract the
evolution of the growth factor and Hubble parameter over this range, and
provide useful constraints on the presence of dark energy at z>2.Comment: 14 pages, 17 figures, accepted to MNRAS; minor changes made (section
2) and references adde
Detection of large scale intrinsic ellipticity-density correlation from the Sloan Digital Sky Survey and implications for weak lensing surveys
The power spectrum of weak lensing shear caused by large-scale structure is
an emerging tool for precision cosmology, in particular for measuring the
effects of dark energy on the growth of structure at low redshift. One
potential source of systematic error is intrinsic alignments of ellipticities
of neighbouring galaxies (II correlation) that could mimic the correlations due
to lensing. A related possibility pointed out by Hirata and Seljak (2004) is
correlation between the intrinsic ellipticities of galaxies and the density
field responsible for gravitational lensing shear (GI correlation). We present
constraints on both the II and GI correlations using 265 908 spectroscopic
galaxies from the SDSS, and using galaxies as tracers of the mass in the case
of the GI analysis. The availability of redshifts in the SDSS allows us to
select galaxies at small radial separations, which both reduces noise in the
intrinsic alignment measurement and suppresses galaxy- galaxy lensing (which
otherwise swamps the GI correlation). While we find no detection of the II
correlation, our results are nonetheless statistically consistent with recent
detections found using the SuperCOSMOS survey. In contrast, we have a clear
detection of GI correlation in galaxies brighter than L* that persists to the
largest scales probed (60 Mpc/h) and with a sign predicted by theoretical
models. This correlation could cause the existing lensing surveys at z~1 to
underestimate the linear amplitude of fluctuations by as much as 20% depending
on the source sample used, while for surveys at z~0.5 the underestimation may
reach 30%. (Abridged.)Comment: 16 pages, matches version published in MNRAS (only minor changes in
presentation from original version
Mapping the allowed parameter space for decaying dark matter models
I consider constraints on a phenomenological decaying-dark-matter model, in
which two weakly-interacting massive particle (WIMP) species have a small mass
splitting, and in which the heavier particle decays to the lighter particle and
a massless particle on cosmological timescales. The decay parameter space is
parameterized by , the speed of the lighter particle in the center-of-mass
frame of the heavier particle prior to decay, and the decay time . Since
I consider the case in which dark-matter halos have formed before there has
been significant decay, I focus on the effects of decay in already-formed
halos. I show that the parameter space may be constrained by
observed properties of dark-matter halos. I highlight which set of observations
is likely to yield the cleanest constraints on parameter space, and
calculate the constraints in those cases in which the effect of decay on the
observables can be calculated without N-body simulations of decaying dark
matter. I show that for km s, the z=0 galaxy
cluster mass function and halo mass-concentration relation constrain 40 Gyr, and that precise constraints on for smaller will
require N-body simulations.Comment: 14 pages, 5 figures, references added, replaced to match version
published in Phys. Rev.
Improved optical mass tracer for galaxy clusters calibrated using weak lensing measurements
We develop an improved mass tracer for clusters of galaxies from optically observed parameters, and calibrate the mass relation using weak gravitational lensing measurements. We employ a sample of ∼13 000 optically selected clusters from the Sloan Digital Sky Survey (SDSS) maxBCG catalogue, with photometric redshifts in the range 0.1-0.3. The optical tracers we consider are cluster richness, cluster luminosity, luminosity of the brightest cluster galaxy (BCG) and combinations of these parameters. We measure the weak lensing signal around stacked clusters as a function of the various tracers, and use it to determine the tracer with the least amount of scatter. We further use the weak lensing data to calibrate the mass normalization. We find that the best mass estimator for massive clusters is a combination of cluster richness, N200, and the luminosity of the BCG, LBCG: , where is the observed mean BCG luminosity at a given richness. This improved mass tracer will enable the use of galaxy clusters as a more powerful tool for constraining cosmological parameter
Improved optical mass tracer for galaxy clusters calibrated using weak lensing measurements
We develop an improved mass tracer for clusters of galaxies from optically observed
parameters, and calibrate the mass relation using weak gravitational lensing measurements.
We employ a sample of ~13 000 optically selected clusters from the Sloan Digital Sky
Survey (SDSS) maxBCG catalogue, with photometric redshifts in the range 0.1–0.3. The
optical tracers we consider are cluster richness, cluster luminosity, luminosity of the brightest
cluster galaxy (BCG) and combinations of these parameters. We measure the weak
lensing signal around stacked clusters as a function of the various tracers, and use it to
determine the tracer with the least amount of scatter. We further use the weak lensing
data to calibrate the mass normalization. We find that the best mass estimator for massive
clusters is a combination of cluster richness, N200, and the luminosity of the BCG, LBCG: M200p = (1.27 ±0.08)(N200/20)^1.20±0.09[LBCG/LBCG(N200)]^0.71±0.14 × 10^14 h
^−1M⊙, where LBCG(N200) is the observed mean BCG luminosity at a given richness. This improved mass
tracer will enable the use of galaxy clusters as a more powerful tool for constraining cosmological
parameters
The Masses and Shapes of Dark Matter Halos from Galaxy-Galaxy Lensing in the CFHTLS
We present the first galaxy-galaxy weak lensing results using early data from
the Canada-France-Hawaii Telescope Legacy Survey (CFHTLS). These results are
based on ~22 sq. deg. of i' data. From this data, we estimate the average
velocity dispersion for an L* galaxy at a redshift of 0.3 to be 137 +- 11 km/s,
with a virial mass, M_{200}, of 1.1 +- 0.2 \times 10^{12} h^{-1} Msun and a
rest frame R-band mass-to-light ratio of 173 +- 34 h Msun/Lsun. We also
investigate various possible sources of systematic error in detail.
Additionally, we separate our lens sample into two sub-samples, divided by
apparent magnitude, thus average redshift. From this early data we do not
detect significant evolution in galaxy dark matter halo mass-to-light ratios
from a redshift of 0.45 to 0.27. Finally, we test for non-spherical galaxy dark
matter halos. Our results favor a dark matter halo with an ellipticity of ~0.3
at the 2-sigma level when averaged over all galaxies. If the sample of
foreground lens galaxies is selected to favor ellipticals, the mean halo
ellipticity and significance of this result increase.Comment: 12 pages, 11 figures, accepted to ApJ, uses emulateap
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