INSPIRE-HEP Profile: http://inspirehep.net/author/profile/Paul.M.Carter.1
Low Redshift Baryon Acoustic Oscillation Measurement from the 6-degree Field Galaxy Survey
Paul Carter, Florian Beutler, Will J Percival, Chris Blake, Jun Koda, Ashley J Ross
Low-redshift measurements of baryon acoustic oscillations (BAO) measure the late-time evolution of the Universe and are a vital probe of dark energy. Over the past decade both the 6-degree Field Galaxy Survey (6dFGS) and Sloan Digital Sky Survey Main Galaxy Sample (SDSS MGS) have provided important distance constraints at |𝑧z| < 0.3. In this paper we re-evaluate the cosmological information from the BAO detection in 6dFGS making use of halo occupation distribution (HOD)-populated COmoving Lagrangian Acceleration (COLA) mocks for an accurate covariance matrix and take advantage of the now commonly implemented technique of density field reconstruction. For the 6dFGS data, we find consistency with the previous analysis, and obtain an isotropic volume-averaged distance measurement of |𝐷𝑉(𝑧eff=0.097)=[372±17(±9833)](𝑟𝑠/𝑟fid𝑠)MpcDV(zeff=0.097)=[372±17(±3398)](rs/rsfid)Mpc| but with a highly non-Gaussian likelihood. We combine our measurement from both the post-reconstruction clustering of 6dFGS and SDSS MGS offering an updated constraint in this redshift regime, |𝐷𝑉(𝑧eff=0.122)=[539±17(±3539)](𝑟𝑠/𝑟fid𝑠)MpcDV(zeff=0.122)=[539±17(±3935)](rs/rsfid)Mpc|. This measurement tightens the constraint in comparison to the result from SDSS MGS alone, especially at the 2σ and higher significance levels. These measurements are consistent with standard Λcold dark matter (ΛCDM) and after fixing the standard ruler using a Planck prior on Ω_mh^2, the joint analysis gives |𝐻0=64.0±3.5kms−1Mpc−1H0=64.0±3.5kms−1Mpc−1|. This result is consistent with other BAO and Cosmic microwave background (CMB) studies but is in >2σ tension with supernova distance ladder measurements. In the near future both the Taipan Galaxy Survey and the Dark Energy Spectroscopic Instrument (DESI) will improve this measurement to |1%1%| at low redshift.
The Impact of the Fiducial Cosmology Assumption on BAO Distance Scale Measurements
Paul Carter, Florian Beutler, Will J. Percival, Joseph DeRose, Risa H. Wechsler, Cheng Zhao
Standard analysis pipelines for measurements of Baryon Acoustic Oscillations (BAO) in galaxy surveys make use of a fiducial cosmological model to guide the data compression required to transform from observed redshifts and angles to the measured angular and radial BAO peak positions. In order to remove any dependence on the fiducial cosmology from the results, all models compared to the data should mimic the compression and its dependence on the fiducial model. In practice, approximations are made when testing models: (1) There is assumed to be no residual dependence on the fiducial cosmology after reconstruction, (2) differences in the distance--redshift relationship are assumed to match a linear scaling, and (3) differences in clustering between true and fiducial models are assumed to be removed by the free parameters used to null the non-BAO signal. We test these approximations using the current standard measurement procedure with a set of halo catalogs from the {\sc Aemulus} suite of 𝑁N-body simulations, which span a range of 𝑤CDMwCDM cosmological models. We focus on reconstruction of the primordial BAO and locating the BAO. For the range of 𝑤CDMwCDM cosmologies covered by the {\sc Aemulus} suite, we find no evidence for systematic errors in the measured BAO shift parameters 𝛼∥α∥ and 𝛼⊥α⊥ to <0.1%<0.1%. However, the measured errors 𝜎𝛼∥σα∥ and 𝜎𝛼⊥σα⊥ show a notable absolute increase by up to +0.001+0.001 and +0.002+0.002 respectively in the case that the fiducial cosmology does not match the truth. These effects on the inferred BAO scale will be important given the precision of measurements expected from future surveys including DESI, Euclid, and WFIRST.
Link: https://doi.org/10.1093/mnras/staa761
Beyond BAO: Improving cosmological constraints from BOSS data with measurement of the void-galaxy cross-correlation
Seshadri Nadathur, Paul M. Carter, Will J. Percival, Hans A. Winther, Julian Bautista
We present a measurement of the anisotropic void-galaxy cross-correlation function in the CMASS galaxy sample of the BOSS DR12 data release. We perform a joint fit to the data for redshift space distortions (RSD) due to galaxy peculiar velocities and anisotropies due to the Alcock-Paczynski (AP) effect, for the first time using a velocity field reconstruction technique to remove the complicating effects of RSD in the void center positions themselves. Fits to the void-galaxy function give a 1% measurement of the AP parameter combination DA(z)H(z)/c=0.4367±0.0045 at redshift z=0.57, where DA is the angular diameter distance and H the Hubble parameter, exceeding the precision obtainable from baryon acoustic oscillations (BAO) by a factor of ∼3.5 and free of systematic errors. From voids alone we also obtain a 10% measure of the growth rate, fσ8(z=0.57)=0.501±0.051. The parameter degeneracies are orthogonal to those obtained from galaxy clustering. Combining void information with that from BAO and galaxy RSD in the same CMASS sample, we measure DA(0.57)/rs=9.383±0.077 (at 0.8% precision), H(0.57)rs=(14.05±0.14)103 kms-1 Mpc-1 (1%), and fσ8=0.453±0.022 (4.9%), consistent with cosmic microwave background (CMB) measurements from Planck. These represent a factor ∼2 improvement in precision over previous results through the inclusion of void information. Fitting a flat cosmological constant ΛCDM model to these results in combination with Planck CMB data, we find up to an 11% reduction in uncertainties on H0 and Ωm compared to use of the corresponding BOSS consensus values. Constraints on extended models with nonflat geometry and a dark energy of state that differs from w=-1 show an even greater improvement.
Link: https://doi.org/10.1103/PhysRevD.100.023504
A Zeldovich reconstruction method for measuring redshift space distortions using cosmic voids
Seshadri Nadathur, Paul Carter, Will Percival
Redshift space distortions (RSD) in the void–galaxy correlation ξ^s provide information on the linear growth rate of structure in low density environments. Accurate modelling of these RSD effects can also allow the use of voids in competitive Alcock–Paczynski measurements. Linear theory models of ξ^s are able to provide extremely good descriptions of simulation data on all scales provided the real space void positions are known. However, by reference to simulation data we demonstrate the failure of the assumptions implicit in current models of ξ^s for voids identified directly in redshift space, as would be simplest using real observational data. To overcome this problem we instead propose using a density-field reconstruction method based on the Zeldovich approximation to recover the real space void positions from redshift space data. We show that this recovers the excellent agreement between theory and data for ξ^s. Performing the reconstruction requires an input cosmological model so, to be self-consistent, we have to perform reconstruction for every model to be tested. We apply this method to mock galaxy and void catalogues in the Big MultiDark N-body simulation and consistently recover the fiducial growth rate to a precision of |3.4 per cent3.4 per cent| using the simulation volume of (2.5 h^−1Gpc)^3.
Link: https://academic.oup.com/mnras/article-abstract/482/2/2459/5133415
Overview of the DESI Legacy Imaging Surveys
DESI Collaboration (Arjun Dey (NRAO, Tucson) et al.)
The DESI Legacy Imaging Surveys (http://legacysurvey.org/) are a combination of three public projects (the Dark Energy Camera Legacy Survey, the Beijing–Arizona Sky Survey, and the Mayall z-band Legacy Survey) that will jointly image ≈14,000 deg2 of the extragalactic sky visible from the northern hemisphere in three optical bands (g, r, and z) using telescopes at the Kitt Peak National Observatory and the Cerro Tololo Inter-American Observatory. The combined survey footprint is split into two contiguous areas by the Galactic plane. The optical imaging is conducted using a unique strategy of dynamically adjusting the exposure times and pointing selection during observing that results in a survey of nearly uniform depth. In addition to calibrated images, the project is delivering a catalog, constructed by using a probabilistic inference-based approach to estimate source shapes and brightnesses. The catalog includes photometry from the grz optical bands and from four mid-infrared bands (at 3.4, 4.6, 12, and 22 μm) observed by the Wide-field Infrared Survey Explorer satellite during its full operational lifetime. The project plans two public data releases each year. All the software used to generate the catalogs is also released with the data. This paper provides an overview of the Legacy Surveys project.
Link: https://iopscience.iop.org/article/10.3847/1538-3881/ab089d
Power spectrum multipoles on the curved sky: an application to the 6-degree Field Galaxy Survey
Chris Blake, Paul Carter, Jun Koda
The peculiar velocities of galaxies cause their redshift-space clustering to depend on the angle to the line of sight, providing a key test of gravitational physics on cosmological scales. These effects may be described using a multipole expansion of the clustering measurements. Focussing on Fourier-space statistics, we present a new analysis of the effect of the survey window function, and the variation of the line of sight across a survey, on the modelling of power spectrum multipoles. We determine the joint covariance of the Fourier-space multipoles in a Gaussian approximation, and indicate how these techniques may be extended to studies of overlapping galaxy populations via multipole cross-power spectra. We apply our methodology to one of the widest area galaxy redshift surveys currently available, the 6-degree Field Galaxy Survey, deducing a normalized growth rate fσ_8(|𝑧z| = 0.06) = 0.38 ± 0.12 in the low-redshift Universe, in agreement with previous analyses of this data set using different techniques. Our framework should be useful for processing future wide-angle galaxy redshift surveys.
Link: https://academic.oup.com/mnras/article-abstract/479/4/5168/5050079
Consistency of the growth rate in different environments with the 6-degree Field Galaxy Survey: Measurement of the void-galaxy and galaxy-galaxy correlation function
Ixandra Achitouv, Chris Blake, P. Carter, J. Koda, F. Beutler
We present a new test of gravitational physics by comparing the growth rate of cosmic structure measured around voids with that measured around galaxies in the same large-scale structure data set: the low-redshift 6-degree Field Galaxy Survey. By fitting a redshift space distortion model to the two-dimensional galaxy-galaxy and void-galaxy correlation functions, we recover the growth rate values fσ8=0.42±0.06 and 0.39±0.11, respectively. The environmental dependence of cosmological statistics can potentially discriminate between modified-gravity scenarios which modulate the growth rate as a function of scale or environment and test the underlying assumptions of homogeneity and isotropy.
Link: https://journals.aps.org/prd/abstract/10.1103/PhysRevD.95.083502