1,135 research outputs found
The effect of redshift-space distortions on projected 2-pt clustering measurements
Although redshift-space distortions only affect inferred distances and not
angles, they still distort the projected angular clustering of galaxy samples
selected using redshift dependent quantities. From an Eulerian view-point, this
effect is caused by the apparent movement of galaxies into or out of the
sample. From a Lagrangian view-point, we find that projecting the
redshift-space overdensity field over a finite radial distance does not remove
all the anisotropic distortions. We investigate this effect, showing that it
strongly boosts the amplitude of clustering for narrow samples and can also
reduce the significance of baryonic features in the correlation function. We
argue that the effect can be mitigated by binning in apparent galaxy
pair-centre rather than galaxy position, and applying an upper limit to the
radial galaxy separation. We demonstrate this approach, contrasting against
standard top-hat binning in galaxy distance, using sub-samples taken from the
Hubble Volume simulations. Using a simple model for the radial distribution
expected for galaxies from a survey such as the Dark Energy Survey (DES), we
show that this binning scheme will simplify analyses that will measure baryon
acoustic oscillations within such galaxy samples. Comparing results from
different binning schemes has the potential to provide measurements of the
amplitude of the redshift-space distortions. Our analysis is relevant for other
photometric redshift surveys, including those made by the Panoramic Survey
Telescope & Rapid Response System (Pan-Starrs) and the Large Synoptic Survey
Telescope (LSST).Comment: 13 pages, 15 figures, accepted by MNRAS, corrected typos, revised
argument in section 3, figure added in section 3, results unchange
The significance of the integrated Sachs-Wolfe effect revisited
We revisit the state of the integrated Sachs-Wolfe (ISW) effect measurements
in light of newly available data and address criticisms about the measurements
which have recently been raised. We update the data set previously assembled by
Giannantonio et al. to include new data releases for both the cosmic microwave
background (CMB) and the large-scale structure (LSS) of the Universe. We find
that our updated results are consistent with previous measurements. By fitting
a single template amplitude, we now obtain a combined significance of the ISW
detection at the 4.4 sigma level, which fluctuates by 0.4 sigma when
alternative data cuts and analysis assumptions are considered. We also make new
tests for systematic contaminations of the data, focusing in particular on the
issues raised by Sawangwit et al. Amongst them, we address the rotation test,
which aims at checking for possible systematics by correlating pairs of
randomly rotated maps. We find results consistent with the expected data
covariance, no evidence for enhanced correlation on any preferred axis of
rotation, and therefore no indication of any additional systematic
contamination. We publicly release the results, the covariance matrix, and the
sky maps used to obtain them.Comment: 19 pages, 10 figures. MNRAS in pres
Modeling the reconstructed BAO in Fourier space
The density field reconstruction technique, which was developed to partially
reverse the nonlinear degradation of the Baryon Acoustic Oscillation (BAO)
feature in the galaxy redshift surveys, has been successful in substantially
improving the cosmology constraints from recent galaxy surveys such as Baryon
Oscillation Spectroscopic Survey (BOSS). We estimate the efficiency of the
reconstruction method as a function of various reconstruction details. To
directly quantify the BAO information in nonlinear density fields before and
after reconstruction, we calculate the cross-correlations (i.e., propagators)
of the pre(post)-reconstructed density field with the initial linear field
using a mock galaxy sample that is designed to mimic the clustering of the BOSS
CMASS galaxies. The results directly provide the BAO damping as a function of
wavenumber that can be implemented into the Fisher matrix analysis. We focus on
investigating the dependence of the propagator on a choice of smoothing filters
and on two major different conventions of the redshift-space density field
reconstruction that have been used in literature. By estimating the BAO
signal-to-noise for each case, we predict constraints on the angular diameter
distance and Hubble parameter using the Fisher matrix analysis. We thus
determine an optimal Gaussian smoothing filter scale for the signal-to-noise
level of the BOSS CMASS. We also present appropriate BAO fitting models for
different reconstruction methods based on the first and second order Lagrangian
perturbation theory in Fourier space. Using the mock data, we show that the
modified BAO fitting model can substantially improve the accuracy of the BAO
position in the best fits as well as the goodness of the fits.Comment: 21 pages, 7 figures, 1 table. Minor revisions. Matches version
accepted by MNRA
Redshift Weights for Baryon Acoustic Oscillations : Application to Mock Galaxy Catalogs
Large redshift surveys capable of measuring the Baryon Acoustic Oscillation
(BAO) signal have proven to be an effective way of measuring the
distance-redshift relation in cosmology. Building off the work in Zhu et al.
(2015), we develop a technique to directly constrain the distance-redshift
relation from BAO measurements without splitting the sample into redshift bins.
We parametrize the distance-redshift relation, relative to a fiducial model, as
a quadratic expansion. We measure its coefficients and reconstruct the
distance-redshift relation from the expansion. We apply the redshift weighting
technique in Zhu et al. (2015) to the clustering of galaxies from 1000 QuickPM
(QPM) mock simulations after reconstruction and achieve a 0.75% measurement of
the angular diameter distance at and the same precision for
Hubble parameter H at . These QPM mock catalogs are designed to mimic
the clustering and noise level of the Baryon Oscillation Spectroscopic Survey
(BOSS) Data Release 12 (DR12). We compress the correlation functions in the
redshift direction onto a set of weighted correlation functions. These
estimators give unbiased and measurements at all redshifts within the
range of the combined sample. We demonstrate the effectiveness of redshift
weighting in improving the distance and Hubble parameter estimates. Instead of
measuring at a single 'effective' redshift as in traditional analyses, we
report our and measurements at all redshifts. The measured fractional
error of ranges from 1.53% at to 0.75% at . The
fractional error of ranges from 0.75% at to 2.45% at .
Our measurements are consistent with a Fisher forecast to within 10% to 20%
depending on the pivot redshift. We further show the results are robust against
the choice of fiducial cosmologies, galaxy bias models, and RSD streaming
parameters.Comment: 13 pages, 8 figures, submitted to MNRA
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The Clustering of the SDSS DR7 Main Galaxy Sample I: A 4 per cent Distance Measure at z=0.15
We create a sample of spectroscopically identified galaxies with
from the Sloan Digital Sky Survey (SDSS) Data Release 7, covering 6813 deg.
Galaxies are chosen to sample the highest mass haloes, with an effective bias
of 1.5, allowing us to construct 1000 mock galaxy catalogs (described in Paper
II), which we use to estimate statistical errors and test our methods. We use
an estimate of the gravitational potential to "reconstruct" the linear density
fluctuations, enhancing the Baryon Acoustic Oscillation (BAO) signal in the
measured correlation function and power spectrum. Fitting to these
measurements, we determine Mpc; this is a better than 4 per cent distance measurement. This "fills
the gap" in BAO distance ladder between previously measured local and higher
redshift measurements, and affords significant improvement in constraining the
properties of dark energy. Combining our measurement with other BAO
measurements from BOSS and 6dFGS galaxy samples provides a 15 per cent
improvement in the determination of the equation of state of dark energy and
the value of the Hubble parameter at (). Our measurement is fully
consistent with the Planck results and the CDM concordance cosmology,
but increases the tension between PlanckBAO determinations and direct
measurements.Comment: Accepted by MNRAS, distance likelihood is available in source file
Cosmological constraints from the convergence 1-point probability distribution
We examine the cosmological information available from the 1-point
probability distribution (PDF) of the weak-lensing convergence field, utilizing
fast L-PICOLA simulations and a Fisher analysis. We find competitive
constraints in the - plane from the convergence PDF with
pixels compared to the cosmic shear power spectrum with an
equivalent number of modes (). The convergence PDF also partially
breaks the degeneracy cosmic shear exhibits in that parameter space. A joint
analysis of the convergence PDF and shear 2-point function also reduces the
impact of shape measurement systematics, to which the PDF is less susceptible,
and improves the total figure of merit by a factor of , depending on the
level of systematics. Finally, we present a correction factor necessary for
calculating the unbiased Fisher information from finite differences using a
limited number of cosmological simulations.Comment: 10 pages, 5 figure
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