1,721,083 research outputs found
Optimal weights for measuring redshift space distortions in multitracer galaxy catalogues
Full text linkCitation: Pearson, D. W., Samushia, L., & Gagrani, P. (2016). Optimal weights for measuring redshift space distortions in multitracer galaxy catalogues. Monthly Notices of the Royal Astronomical Society, 463(3), 2708-2715. doi:10.1093/mnras/stw2177Since the volume accessible to galaxy surveys is fundamentally limited, it is extremely important to analyse available data in the most optimal fashion. One way of enhancing the cosmological information extracted from the clustering of galaxies is by weighting the galaxy field. The most widely used weighting schemes assign weights to galaxies based on the average local density in the region (FKP weights) and their bias with respect to the dark matter field (PVP weights). They are designed to minimize the fractional variance of the galaxy power-spectrum. We demonstrate that the currently used bias dependent weighting scheme can be further optimized for specific cosmological parameters. We develop a procedure for computing the optimal weights and test them against mock catalogues for which the values of all fitting parameters, as well as the input power-spectrum are known. We show that by applying these weights to the joint power-spectrum of emission line galaxies and luminous red galaxies from the Dark Energy Spectroscopic Instrument survey, the variance in the measured growth rate parameter can be reduced by as much as 36 per cent
Information content of the angular multipoles of redshift-space galaxy bispectrum
Full text linkCitation: Gagrani, P., & Samushia, L. (2017). Information content of the angular multipoles of redshift-space galaxy bispectrum. Monthly Notices of the Royal Astronomical Society, 467(1), 928-934. doi:10.1093/mnras/stx135The redshift-space bispectrum (three point statistics) of galaxies depends on the expansion rate, the growth rate and the geometry of the Universe, and hence can be used to measure key cosmological parameters. In a homogeneous Universe, the bispectrum is a function of five variables and unlike its two point statistics counterpart - the power spectrum - which is a function of only two variables - is difficult to analyse unless the information is somehow reduced. The most commonly considered reduction schemes rely on computing angular integrals over possible orientations of the bispectrum triangle, thus reducing it to sets of function of only three variables describing the triangle shape. We use Fisher information formalism to study the information loss associated with this angular integration. Without any reduction, the bispectrum alone can deliver constraints on the growth rate parameter f that are better by a factor of 2.5 compared with the power spectrum, for a sample of luminous red galaxies expected from near future galaxy surveys at a redshift of z similar to 0.65 if we consider all the wavenumbers up to k <= 0.2 h Mpc (1). At lower redshifts the improvement could be up to a factor of 3. We find that most of the information is in the azimuthal averages of the first three even multipoles. This suggests that the bispectrum of every configuration can be reduced to just three numbers (instead of a 2D function) without significant loss of cosmologically relevant information
Unbiased contaminant removal for 3D galaxy power spectrum measurements
Full text linkWe assess and develop techniques to remove contaminants when calculating the
3D galaxy power spectrum. We separate the process into three separate stages:
(i) removing the contaminant signal, (ii) estimating the uncontaminated
cosmological power spectrum, (iii) debiasing the resulting estimates. For (i),
we show that removing the best-fit contaminant mode subtraction), and setting
the contaminated components of the covariance to be infinite (mode
deprojection) are mathematically equivalent. For (ii), performing a Quadratic
Maximum Likelihood (QML) estimate after mode deprojection gives an optimal
unbiased solution, although it requires the manipulation of large matrices ( being the total number of modes)}, which is
unfeasible for recent 3D galaxy surveys. Measuring a binned average of the
modes for (ii) as proposed by \citet*[FKP]{Feldman} is faster and simpler, but
is sub-optimal and gives rise to a biased solution. We present a method to
debias the resulting FKP measurements that does not require any large matrix
calculations. We argue that the sub-optimality of the FKP estimator compared
with the QML estimator, caused by contaminants is less severe than that
commonly ignored due to the survey window.Comment: 10 pages, 4 figures; version equivalent to accepted articl
Beyond dark energy Fisher forecasts: how DESI will constrain LCDM and quintessence models
Full text linkWe baseline with current cosmological observations to forecast the power of
the Dark Energy Spectroscopic Instrument (DESI) in two ways: 1. the gain in
constraining power of parameter combinations in the standard CDM
model, and 2. the reconstruction of quintessence models of dark energy. For the
former task we use a recently developed formalism to extract the leading
parameter combinations constrained by different combinations of cosmological
survey data. For the latter, we perform a non-parametric reconstruction of
quintessence using the Effective Field Theory of Dark Energy. Using mock DESI
observations of the Hubble parameter, angular diameter distance, and growth
rate, we find that DESI will provide significant improvements over current
datasets on CDM and quintessence constraints. Including DESI mocks in
our CDM analysis improves constraints on , , and
by a factor of two, where the improvement results almost entirely
from the angular diameter distance and growth of structure measurements. Our
quintessence reconstruction suggests that DESI will considerably improve
constraints on a range of quintessence properties, such as the reconstructed
potential, scalar field excursion, and the dark energy equation of state. The
angular diameter distance measurements are particularly constraining in the
presence of a non-CDM signal in which the potential cannot be
accounted for by shifts in and
The clustering of galaxies in the completed SDSS-III Baryon Oscillation Spectroscopic Survey: cosmological implications of the Fourier space wedges of the final sample
Full text linkCitation: Grieb, J. N., Sanchez, A. G., Salazar-Albornoz, S., Scoccimarro, R., Crocce, M., Dalla Vecchia, C., . . . Zhao, G. B. (2017). The clustering of galaxies in the completed SDSS-III Baryon Oscillation Spectroscopic Survey: cosmological implications of the Fourier space wedges of the final sample. Monthly Notices of the Royal Astronomical Society, 467(2), 2085-2112. doi:10.1093/mnras/stw3384We extract cosmological information from the anisotropic power-spectrummeasurements from the recently completed Baryon Oscillation Spectroscopic Survey (BOSS), extending the concept of clustering wedges to Fourier space. Making use of new fast-Fourier-transform-based estimators, we measure the power-spectrum clustering wedges of the BOSS sample by filtering out the information of Legendre multipoles l > 4. Our modelling of these measurements is based on novel approaches to describe non-linear evolution, bias and redshift-space distortions, which we test using synthetic catalogues based on large-volume N-body simulations. We are able to include smaller scales than in previous analyses, resulting in tighter cosmological constraints. Using three overlapping redshift bins, we measure the angular-diameter distance, the Hubble parameter and the cosmic growth rate, and explore the cosmological implications of our full-shape clustering measurements in combination with cosmic microwave background and Type Ia supernova data. Assuming a Lambda cold dark matter (Lambda CDM) cosmology, we constrain the matter density to Omega M = 0.311(-0.010)(+ 0.009) and the Hubble parameter to H-0 = 67.6(-0.6)(+0.7) km s(-1) Mpc(-1), at a confidence level of 68 per cent. We also allow for nonstandard dark energy models and modifications of the growth rate, finding good agreement with the Lambda CDM paradigm. For example, we constrain the equation-of-state parameter to omega =-1.019(-0.039)(+0.048) . This paper is part of a set that analyses the final galaxy-clustering data set from BOSS. The measurements and likelihoods presented here are combined with others in Alam et al. to produce the final cosmological constraints from BOSS
The clustering of galaxies in the SDSS-III Baryon Oscillation Spectroscopic Survey:modeling the clustering and halo occupation distribution of BOSS-CMASS galaxies in the Final Data Release
Full text linkCitation: Rodriguez-Torres, S. A., Chuang, C. H., Prada, F., Guo, H., Klypin, A., Behroozi, P., . . . Thomas, D. (2016). The clustering of galaxies in the SDSS-III Baryon Oscillation Spectroscopic Survey: modelling the clustering and halo occupation distribution of BOSS CMASS galaxies in the Final Data Release. Monthly Notices of the Royal Astronomical Society, 460(2), 1173-1187. doi:10.1093/mnras/stw1014We present a study of the clustering and halo occupation distribution of Baryon Oscillation Spectroscopic Survey (BOSS) CMASS galaxies in the redshift range 0.43 cold dark matter Planck cosmology. We compare the observational data with the simulated ones on a light cone constructed from 20 subsequent outputs of the simulation. Observational effects such as incompleteness, geometry, veto masks and fibre collisions are included in the model, which reproduces within 1 sigma errors the observed monopole of the two-point correlation function at all relevant scales: from the smallest scales, 0.5 h(-1) Mpc, up to scales beyond the baryon acoustic oscillation feature. This model also agrees remarkably well with the BOSS galaxy power spectrum (up to k similar to 1 h Mpc(-1)), and the three-point correlation function. The quadrupole of the correlation function presents some tensions with observations. We discuss possible causes that can explain this disagreement, including target selection effects. Overall, the standard HAM model describes remarkably well the clustering statistics of the CMASS sample. We compare the stellar-to-halo mass relation for the CMASS sample measured using weak lensing in the Canada-France-Hawaii Telescope Stripe 82 Survey with the prediction of our clustering model, and find a good agreement within 1 sigma. The BigMD-BOSS light cone including properties of BOSS galaxies and halo properties is made publicly available
Constraining scalar field dark energy with cosmological observations
Full text linkDoctor of PhilosophyDepartment of PhysicsBharat RatraHigh precision cosmological observations in last decade suggest that about 70% of our universe's energy density is in so called "Dark Energy" (DE). Observations show that DE has negative effective pressure and therefore unlike conventional energy sources accelerates the cosmic expansion instead of decelerating it. DE is highly uniform and has become a dominant component only recently.
The simplest candidate for DE is the time-independent cosmological constant. Although successful in fitting available data, the cosmological constant model has a number of theoretical shortcomings and because of that alternative models of DE are considered. In one such scenario a cosmological scalar field that slowly rolls down its potential acts like a time-dependent cosmological constant.
I have used different independent cosmological data sets to constrain the time dependence of DE's energy density in the framework of the slowly-rolling cosmological scalar field model. Present data favors a time-independent cosmological constant, but the time-dependent DE can not be ruled out at high confidence level. Ongoing and planned cosmological probes and surveys will provide more and better quality data over the next decade. When the new data sets are available we will be able to either detect the time dependence of DE or constrain it to a very small physically uninteresting value
Effects of cosmological model assumptions on galaxy redshift survey measurements
No full textThe clustering of galaxies observed in future redshift surveys will provide a wealth of cosmological information. Matching the signal at different redshifts constrains the dark energy driving the acceleration of the expansion of the Universe. In tandem with these geometrical constraints, redshift-space distortions depend on the build up of large-scale structure. As pointed out by many authors, measurements of these effects are intrinsically coupled. We investigate this link and argue that it strongly depends on the cosmological assumptions adopted when analysing data. Using representative assumptions for the parameters of the Euclid survey in order to provide a baseline future experiment, we show how the derived constraints change due to different model assumptions. We argue that even the assumption of a Friedman-Robertson-Walker space-time is sufficient to reduce the importance of the coupling to a significant degree. Taking this idea further, we consider how the data would actually be analysed and argue that we should not expect to be able to simultaneously constrain multiple deviations from the standard Λ cold dark matter (ΛCDM) model. We therefore consider different possible ways in which the Universe could deviate from the ΛCDM model, and show how the coupling between geometrical constraints and structure growth affects the measurement of such deviations
Forecasting cosmological parameter constraints from near-future space-based galaxy surveys
Full text linkThe next generation of space-based galaxy surveys is expected to measure the growth rate of structure to a level of about one percent over a range of redshifts. The rate of growth of structure as a function of redshift depends on the behavior of dark energy and so can be used to constrain parameters of dark energy models. In this work, we investigate how well these future data will be able to constrain the time dependence of the dark energy density. We consider parameterizations of the dark energy equation of state, such as XCDM and ωCDM, as well as a consistent physical model of time-evolving scalar field dark energy, φCDM.We show that if the standard, specially
flat cosmological model is taken as a fiducial model of the universe, these near-future measurements of structure growth will be able to constrain the time dependence of scalar field dark energy density to a precision of about 10%, which is almost an order of magnitude better than what can be achieved from a compilation of currently available
data sets
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