268 research outputs found
Measuring H0 from the 6dF Galaxy Survey and future low-redshift surveys
Baryon acoustic oscillations (BAO) at low redshift provide a precise and
largely model-independent way to measure the Hubble constant, H0. The 6dF
Galaxy Survey measurement of the BAO scale gives a value of H0 = 67 +/- 3.2
km/s/Mpc, achieving a 1-sigma precision of 5%. With improved analysis
techniques, the planned WALLABY (HI) and TAIPAN (optical) redshift surveys are
predicted to measure H0 to 1-3% precision.Comment: Proceedings of IAU Symposium 289, "Advancing the Physics of Cosmic
Distances", Richard de Grijs & Giuseppe Bono (eds), 2012, 4p
Constraining the relative velocity effect using the Baryon Oscillation Spectroscopic Survey
We analyse the power spectrum of the Baryon Oscillation Spectroscopic Survey
(BOSS), Data Release 12 (DR12) to constrain the relative velocity effect, which
represents a potential systematic for measurements of the Baryon Acoustic
Oscillation (BAO) scale. The relative velocity effect is sourced by the
different evolution of baryon and cold dark matter perturbations before
decoupling. Our power spectrum model includes all -loop redshift-space terms
corresponding to parameterised by the bias parameter . We
also include the linear terms proportional to the relative density,
, and relative velocity dispersion, , which
we parameterise with the bias parameters and . Our data does not support a detection of the relative velocity
effect in any of these parameters. Combining the low and high redshift bins of
BOSS, we find limits of , and with () confidence levels. These constraints
restrict the potential systematic shift in , and ,
due to the relative velocity, to , and , respectively. Given
the current uncertainties on the BAO measurements of BOSS these shifts
correspond to , and for ,
and , respectively
Extending the modeling of the anisotropic galaxy power spectrum to
We present a new model for the redshift-space power spectrum of galaxies and
demonstrate its accuracy in modeling the monopole, quadrupole, and hexadecapole
of the galaxy density field down to scales of .
The model describes the clustering of galaxies in the context of a halo model
and the clustering of the underlying halos in redshift space using a
combination of Eulerian perturbation theory and -body simulations. The
modeling of redshift-space distortions is done using the so-called distribution
function approach. The final model has 13 free parameters, and each parameter
is physically motivated rather than a nuisance parameter, which allows the use
of well-motivated priors. We account for the Finger-of-God effect from centrals
and both isolated and non-isolated satellites rather than using a single
velocity dispersion to describe the combined effect. We test and validate the
accuracy of the model on several sets of high-fidelity -body simulations, as
well as realistic mock catalogs designed to simulate the BOSS DR12 CMASS data
set. The suite of simulations covers a range of cosmologies and galaxy bias
models, providing a rigorous test of the level of theoretical systematics
present in the model. The level of bias in the recovered values of
is found to be small. When including scales to ,
we find 15-30\% gains in the statistical precision of relative to
and a roughly 10-15\% improvement for the
perpendicular Alcock-Paczynski parameter . Using the BOSS DR12
CMASS mocks as a benchmark for comparison, we estimate an uncertainty on that is 10-20\% larger than other similar Fourier-space RSD
models in the literature that use , suggesting
that these models likely have a too-limited parametrization.Comment: Submitted to JCA
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
A complete FFT-based decomposition formalism for the redshift-space bispectrum
To fully extract cosmological information from nonlinear galaxy distribution
in redshift space, it is essential to include higher-order statistics beyond
the two-point correlation function. In this paper, we propose a new
decomposition formalism for computing the anisotropic bispectrum in redshift
space and for measuring it from galaxy samples. Our formalism uses tri-polar
spherical harmonic decomposition with zero total angular momentum to compress
the 3D modes distribution in the redshift-space bispectrum. This approach
preserves three fundamental properties of the Universe: statistical
homogeneity, isotropy, and parity-symmetry, allowing us to efficiently separate
the anisotropic signal induced by redshift-space distortions (RSDs) and the
Alcock-Paczy\'{n}ski (AP) effect from the isotropic bispectrum. The relevant
expansion coefficients in terms of the anisotropic signal are reduced to one
multipole index , and the modes are induced only by the RSD or AP
effects. Our formalism has two advantages: (1) we can make use of Fast Fourier
Transforms (FFTs) to measure the bispectrum; (2) it gives a simple expression
to correct for the survey geometry, i.e., the survey window function. As a
demonstration, we measure the decomposed bispectrum from the Baryon Oscillation
Spectroscopic Survey (BOSS) Data Release 12, and, for the first time, present a
detection of the anisotropic bispectrum in the mode.Comment: 23 pages, 13 figure
Eulerian BAO Reconstructions and N-Point Statistics
As galaxy surveys begin to measure the imprint of baryonic acoustic
oscillations (BAO) on large-scale structure at the sub-percent level,
reconstruction techniques that reduce the contamination from nonlinear
clustering become increasingly important. Inverting the nonlinear continuity
equation, we propose an Eulerian growth-shift reconstruction algorithm that
does not require the displacement of any objects, which is needed for the
standard Lagrangian BAO reconstruction algorithm. In real-space DM-only
simulations the algorithm yields 95% of the BAO signal-to-noise obtained from
standard reconstruction. The reconstructed power spectrum is obtained by adding
specific simple 3- and 4-point statistics to the pre-reconstruction power
spectrum, making it very transparent how additional BAO information from
higher-point statistics is included in the power spectrum through the
reconstruction process. Analytical models of the reconstructed density for the
two algorithms agree at second order. Based on similar modeling efforts, we
introduce four additional reconstruction algorithms and discuss their
performance.Comment: 20+10 pages, 12 figures, included minor improvements to match version
accepted for publicatio
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