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Chameleon fields may modify gravity on cluster scales while recovering general relativity locally. This article reviews signatures of chameleon modifications in the nonlinear cosmological structure, comparing different techniques to model them, summarising the current state of observational constraints, and concluding with an outlook on prospective constraints from future observations and applications of the analytic tools developed in the process to more general scalar-tensor theories. Particular focus is given to the Hu-Sawicki and designer models of gravity.

The secular redshift drift is a potential measurement to directly probe the cosmic expansion. Previous study on the redshift drift mainly focused on the model-dependent simulation. Apparently, the physical insights on the redshift drift are very necessary. So in this paper, it is investigated using thermodynamics on the apparent, Hubble and event horizons. Thermodynamics could analytically present the model-independent upper bounds of redshift drift. For specific assumption on the cosmological parameters, we find that the thermodynamics bounds are nearly one order of magnitude larger than the expectation in standard ΛCDM model. We then examine ten observed redshift drift from Green Bank Telescope at redshift 0.09 < z < 0.69, and find that these observational results are inconsistent with the thermodynamics. The size of the errorbars on these measurements is about three orders of magnitude larger than the effect of thermodynamical bounds for the redshift drift. Obviously, we have not yet hit any instrumental systematics at the shift level of 1m s−1 yr−1.

We present the first measurement of the growth rate of structure at z=0.8. It has been obtained from the redshift-space distortions observed in the galaxy clustering pattern in the VIMOS Public Redshift survey (VIPERS) first data release. VIPERS is a large galaxy redshift survey probing the large-scale structure at 0.5 < z < 1.2 with an unprecedented accuracy. This measurement represents a new reference in the distant Universe, which has been poorly explored until now. We obtain σ8 = 0.47 ± 0.08 at z = 0.8 that is consistent with the predictions of standard cosmological models based on Einstein gravity. This measurement alone is however not accurate enough to allow the detection of possible deviations from standard gravity.

We present the first measurement of the correlation between the map of the CMB lensing potential derived from the Planck nominal mission data and z ≳ 1.5 galaxies detected by Herschel-ATLAS (H-ATLAS) survey covering about 550 deg2. We detect the cross-power spectrum with a significance of ∼ 8.5σ, ruling out the absence of correlation at 9σ. We check detection with a number of null tests. The amplitude of cross-correlation and the galaxy bias are estimated using joint analysis of the cross-power spectrum and the galaxy survey auto-spectrum, which allows to break degeneracy between these parameters. The estimated galaxy bias is consistent with previous estimates of the bias for the H-ATLAS data, while the cross-correlation amplitude is higher than expected for a ΛCDM model. The content of this work is to appear in a forthcoming paper Bianchini, et al. (2014).

Since 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., Comment: 9 pages, 3 figures, 3 tables. Matches accepted version in Monthly Notices of the Royal Astronomical Society

We present a simple fitting formula for the scale-dependent growth rate of Hu-Sawicki model in $f(R)$ modified gravity. We compare the accuracy of the fitting function against numerical results and report achieving a sub-percent maximum error for all different studied cases. The validity of the fitting function is tested against a wide range of scales, $10^{-4} \le k \le 5 \ [\mathrm{Mpc}^{-1}]$ , for various redshift values in the range of $z \in [0.0,\ 3.0]$ and different $|f_R^0|$ values. This formula is useful in producing predictions for cosmological probes that are sensitive to growth rate such as redshift space distortions, galaxy-galaxy correlation function, peculiar velocity statistics and pairwise velocities of galaxy clusters., 15 pages, 7 figures

Author(s): Castorina, E; White, M | Abstract: This is an erratum to the paper 'The Zeldovich approximation and wide-angle redshift-space distortions' by Castorina a White (2018). There is a mistake in equation (37) which should read (Equation Presented) where Σ2 and ξij are defined in the main text. The figures and the conclusions are all unchanged, however this mistake propagates to equation (46) which should read (Equation Presented) Equation (51) then becomes (Equation Presented) Equations (52)-(53) are no longer needed. The change affects equation (63) which should read (Equation Presented) Finally, in Appendix C, equations (C10-C13) should read (Equation Presented).

The Baryon Acoustic Oscillations (BAO) are features in the matter power spectrum on scales of order 100-150 h^{-1} Mpc that promise to be a powerful tool to constrain and test cosmological models. The BAO have attracted such attention that future upcoming surveys have been designed with the BAO at the forefront of the primary science goals. Recent studies have advocated the use of a spherical-Fourier Bessel (sFB) expansion for future wide field surveys that cover both wide and deep regions of the sky necessitating the simultaneous treatment of the spherical sky geometry as well as the extended radial coverage. Ignoring the possible effects of growth, which is not expected to be significant at low redshifts, we present an extended analysis of the BAOs using the sFB formalism by taking into account the role of non-linearities and linear redshift distortions in the oscillations observed in the galaxy power spectrum. The sFB power spectrum has both radial and tangential dependence and it has been shown that in the limit that we approach a deep survey the sFB power spectrum is purely radial and collapses to the Cartesian Fourier power spectrum. This radialisation of information is shown to hold even in the presence of redshift space distortions (RSD) and 1-loop corrections to the galaxy power spectrum albeit with modified tangential and radial dependence. As per previous studies we find that the introduction of non-linearities leads to a damping of the oscillations in the matter power spectrum., Comment: 19 pages, 13 figures. Accepted for publication in MNRAS

The statistical properties of elements of the large-scale structure of the Universe are studied using the SDSS DR7 galaxy catalog and a dark-matter halo catalog obtained via numerical modeling using MultiDark Run1. The minimum spanning tree technique is used to distinguish the large-scale structure, and the Core Sampling method is used to analyze its properties. As a result, the SDSS DR7 and MultiDark Run1 catalogs are divided into subcatalogs of two-dimensonal walls and one-dimensional filaments. Some statistical properties of these subcatalogs are compared with theoretical predictions. The mean separation between the walls is measured using both the observations and numerical modeling results (50–60 Mpc/h) and the distribution of the wall surface density is derived. The fraction of the SDSS DR7 galaxy clusters thought to have been distorted by the observational effect called “fingers of God” is estimated. Dense clusters for which this effect is most appreciable constitute ∼15% of the analyzed clusters. The influence of these clusters on the final result is eliminated by fitting the orientation of test cylinders in the Core Sampling method.

The "tired light" hypothesis interprets the cosmological redshift on an assumption of energy loss of photons interacting with massive particles by some researchers. A new mechanistic model of "tired light" is proposed by establishing a differential equation through the analysis of a photon's energy loss based on the classical electromagnetic theory and principles of the mass energy equivalence and the wave particle duality. The photon transfers some energy to massive particles by Lorentz electric force in their interaction. The expanding result of the equation's solution is a formula for redshift, which shows a relationship of redshift to the wavelength of light and the number of massive particles that the photon encountered. The model agrees with the observational data in the cited literature by the relationship of redshift to wavelength of light. And, the relationship of redshift to the number of massive particles encountered by the photons explains the "limb effect" on the solar disc, the signal redshift of Pioneer 6, and the large redshifts of quasars, all of which cannot be explained by the Doppler effect. The new model provides a basis for the hypothesis of "tired light" to become a reasonable theory. (C) 2013 Physics Essays Publication.

A slight continuous increase of the rest masses and the electric charges of material particles can jus tify quantum phenomena and the cosmological data. This increase can only οccur in a strictly defined way: the law of selfvariations. The law of selfvariations co ndenses into one equation the totality of the cosmo logical data, as we observe them from the time of Hubble up to the present. The consequences of the selfvariat ions are recorded persistently and in the most immediate way in the cosmological data. The observation of t he redshift of distant astronomical objects by Hubble in the beginning of the last century, leads to only one certain conclusion: one or more physical quantities , which we would expect to be constant in the Unive rse, in reality vary. The physical theories of the twent ieth century justify the redshift macroscopically, via the expansion of the Universe. But the redshift can als o be justified differently, with microscopic causes that predict a self-consistent cosmological model in acc ordance with all of the cosmological data. The prob lems caused by modern observations to the Standard Cosmological Model, are exactly focused at the points where the two models make different predictions. We propose a revaluation of the cosmological data, ba sed on the law of the selfvariations.

Objects falling into an overdensity appear larger on its near side and smaller on its far side than other objects at the same redshift. This produces a dipolar pattern of magnification, primarily as a consequence of the Doppler effect. At low redshift this Doppler magnification completely dominates the usual integrated gravitational lensing contribution to the lensing magnification. We show that one can optimally observe this pattern by extracting the dipole in the cross-correlation of number counts and galaxy sizes. This dipole allows us to almost completely remove the contribution from gravitational lensing up to redshift 0.5, and even at high redshift z~1 the dipole picks up the Doppler magnification predominantly. Doppler magnification should be easily detectable in current and upcoming optical and radio surveys; by forecasting for telescopes such as the SKA, we show that this technique is competitive with using peculiar velocities via redshift-space distortions to constrain dark energy. It produces similar yet complementary constraints on the cosmological model to those found using measurements of the cosmic shear., 17 pages, 12 figures. v2: new example of signal-to-noise, minor changes, matches version accepted in MNRAS

The standard relation between the cosmological redshift and cosmic scale factor underlies cosmological inference from virtually all kinds of cosmological observations, leading to the emergence of the LambdaCDM cosmological model. This relation is not a fundamental theory and thus observational determination of this function (redshift remapping) should be regarded as an insightful alternative to holding its standard form in analyses of cosmological data. Here we present non-parametric reconstructions of redshift remapping in dark-matter-dominated models and constraints on cosmological parameters from a joint analysis of all primary cosmological probes including the local measurement of the Hubble constant, Type Ia supernovae, baryonic acoustic oscillations (BAO), Planck observations of the cosmic microwave background (CMB) radiation (temperature power spectrum) and cosmic chronometers. The reconstructed redshift remapping points to an additional boost of redshift operating in late epoch of cosmic evolution, but affecting both low-redshift observations and the CMB. The model predicts a significant difference between the actual Hubble constant, h=0.48+/-0.02, and its local determination, h_obs=0.73+/-0.02. The ratio of these two values coincides closely with the maximum expansion rate inside voids formed in the corresponding open cosmological model with Omega_m=0.87+/-0.03, whereas the actual value of the Hubble constant implies the age of the Universe that is compatible with the Planck LambdaCDM cosmology. The new dark-matter-dominated model with redshift remapping provides excellent fits to all data and eliminates recently reported tensions between the Planck LambdaCDM cosmology, the local determination of the Hubble constant and the BAO measurements from the Ly-alpha forest of high-redshift quasars., 21 pages, 11 figures, 4 tables; accepted for publication in MNRAS

Peculiar velocity surveys present a very promising route to measuring the growth rate of large-scale structure and its scale dependence. However, individual peculiar velocity surveys suffer from large statistical errors due to the intrinsic scatter in the relations used to infer a galaxy's true distance. In this context we use a Fisher Matrix formalism to investigate the statistical benefits of combining multiple peculiar velocity surveys. We find that for all cases we consider there is a marked improvement on constraints on the linear growth rate $f\sigma_{8}$. For example, the constraining power of only a few peculiar velocity measurements is such that the addition of the 2MASS Tully-Fisher survey (containing only $\sim2,000$ galaxies) to the full redshift and peculiar velocity samples of the 6-degree Field Galaxy Survey (containing $\sim 110,000$ redshifts and $\sim 9,000$ velocities) can improve growth rate constraints by $\sim20\%$. Furthermore, the combination of the future TAIPAN and WALLABY+WNSHS surveys has the potential to reach a $\sim3\%$ error on $f\sigma_{8}$, which will place tight limits on possible extensions to General Relativity. We then turn to look at potential systematics in growth rate measurements that can arise due to incorrect calibration of the peculiar velocity zero-point and from scale-dependent spatial and velocity bias. For next generation surveys, we find that neglecting velocity bias in particular has the potential to bias constraints on the growth rate by over $5\sigma$, but that an offset in the zero-point has negligible impact on the velocity power spectrum., Comment: 24 pages, 11 figures, 7 tables. Accepted for publication in MNRAS

Modeling the large-scale structure of the universe on nonlinear scales has the potential to substantially increase the science return of upcoming surveys by increasing the number of modes available for model comparisons. One way to achieve this is to model nonlinear scales perturbatively. Unfortunately, this involves high-dimensional loop integrals that are cumbersome to evaluate. Trying to simplify this, we show how two-loop (next-to-next-to-leading order) corrections to the density power spectrum can be reduced to low-dimensional, radial integrals. Many of those can be evaluated with a one-dimensional Fast Fourier Transform, which is significantly faster than the five-dimensional Monte-Carlo integrals that are needed otherwise. The general idea of this FFT-PT method is to switch between Fourier and position space to avoid convolutions and integrate over orientations, leaving only radial integrals. This reformulation is independent of the underlying shape of the initial linear density power spectrum and should easily accommodate features such as those from baryonic acoustic oscillations. We also discuss how to account for halo bias and redshift space distortions., 13+11 pages, updated discussion of multiple inverse Laplacians

Massive neutrinos leave a unique signature in the large scale clustering of matter. We investigate the wavenumber dependence of the growth factor arising from neutrino masses and use a Fisher analysis to determine the aspects of a galaxy survey needed to measure this scale dependence., 10 pages, 2 figures. v2: a) Shot noise was added to the analysis and figure 2 was modified to include these results. b) typos corrections. c) one new reference added

We analyse the redshift-space (z-space) distortions of QSO clustering in the 2dF QSO Redshift Survey (2QZ). To interpret the z-space correlation function, xi(sigma,pi), we require an accurate model for the QSO real-space correlation function, xi(r). Although a single power-law xi(r) model fits the projected correlation function (wp(sigma)) at small scales, it implies somewhat too shallow a slope for both wp(sigma) and the z-space correlation function, xi(s), at larger scales > 20 h^(-1) Mpc. Motivated by the form for xi(r) seen in the 2dF Galaxy Redshift Survey (2dFGRS) and in standard LCDM predictions, we use a double power-law model for xi(r) which gives a good fit to xi(s) and wp(sigma). The model is parametrized by a slope of gamma=1.45 for 1, Comment: Accepted for publication in MNRAS. 17 pages, 15 figures

The redshift drift of objects moving in the Hubble flow has been proposed as a powerful model-independent probe of the underlying cosmology. A measurement of the first and second order redshift derivatives appears to be well within the reach of upcoming surveys using ELT-HIRES and the SKA Phase 2 array. Here we show that an unambiguous prediction of the R_h=ct cosmology is zero drift at all redshifts, contrasting sharply with all other models in which the expansion rate is variable. For example, multi-year monitoring of sources at redshift z=5 with the ELT-HIRES is expected to show a velocity shift Delta v = -15 cm/s/yr due to the redshift drift in Planck LCDM, while Delta v=0 cm/s/yr in R_h=ct. With an anticipated ELT-HIRES measurement error of +/-5 cm/s/yr after 5 years, these upcoming redshift drift measurements might therefore be able to differentiate between R_h=ct and Planck LCDM at ~3 sigma, assuming that any possible source evolution is well understood. Such a result would provide the strongest evidence yet in favour of the R_h=ct cosmology. With a 20-year baseline, these observations could favor one of these models over the other at better than 5 sigma., 7 pages, 1 figure. Accepted for publication in MNRAS Letters

Measurements of the non-Gaussianity of the primordial density field have the power to considerably improve our understanding of the physics of inflation. Indeed, if we can increase the precision of current measurements by an order of magnitude, a null-detection would rule out many classes of scenarios for generating primordial fluctuations. Large-scale galaxy redshift surveys represent experiments that hold the promise to realise this goal. Thus, we model the galaxy bispectrum and forecast the accuracy with which it will probe the parameter $f_{\rm NL}$, which represents the degree of primordial local-type non Gaussianity. Specifically, we address the problem of modelling redshift space distortions (RSD) in the tree-level galaxy bispectrum including $f_{\rm NL}$. We find novel contributions associated with RSD, with the characteristic large scale amplification induced by local-type non-Gaussianity. These RSD effects must be properly accounted for in order to obtain un-biased measurements of $f_{\rm NL}$ from the galaxy bispectrum. We propose an analytic template for the monopole which can be used to fit against data on large scales, extending models used in the recent measurements. Finally, we perform idealised forecasts on $\sigma_{f_{\rm NL}}$ -- the accuracy of the determination of local non-linear parameter $f_{\rm NL}$ -- from measurements of the galaxy bispectrum. Our findings suggest that current surveys can in principle provide $f_{\rm NL}$ constraints competitive with Planck, and future surveys could improve them further., Comment: 29 pages, 1 figure. v2: minor revision, references added, version to appear in JCAP

Weak lensing (WL) promises to be a particularly sensitive probe of both the growth of large scale structure (LSS) as well as the fundamental relation between matter density perturbations and metric perturbations, thus providing a powerful tool with which we may constrain modified theories of gravity (MG) on cosmological scales. Future deep, wide-field WL surveys will provide an unprecedented opportunity to constrain deviations from General Relativity (GR). Employing a three-dimensional (3D) analysis based on the spherical Fourier-Bessel (sFB) expansion, we investigate the extent to which MG theories will be constrained by a typical 3D WL survey configuration including noise from the intrinsic ellipticity distribution $\sigma_{\epsilon}$ of source galaxies. Here we focus on two classes of screened theories of gravity: i) $f(R)$ chameleon models and ii) environmentally dependent dilaton models. We use one-loop perturbation theory combined with halo models in order to accurately model the evolution of matter power-spectrum with redshift in these theories. Using a Fisher information matrix based approach, we show that for an all-sky spectroscopic survey, the parameter $f_{R_0}$ can be constrained in the range $f_{R_0}< 5\times 10^{-6}(9\times 10^{-6})$ for $n=1(2)$ with a 3$\sigma$ confidence level. This can be achieved by using relatively low order angular harmonics $\ell100$ can further tighten the constraints, making them comparable to current solar-system constraints. We also employ a Principal Component Analysis (PCA) in order to study the parameter degeneracies in the MG parameters. Our results can trivially be extended to other MG theories, such as the K-mouflage models. The confusion from intrinsic ellipticity correlation and modification of the matter power-spectrum at small scale due to feedback mechanisms is briefly discussed., Comment: 25 pages. 10 Figures. 4 Tables. Submitted to PRD

Photometric surveys produce large-area maps of the galaxy distribution, but with less accurate redshift information than is obtained from spectroscopic methods. Modern photometric redshift (photo-z) algorithms use galaxy magnitudes, or colors, that are obtained through multi-band imaging to produce a probability density function (PDF) for each galaxy in the map. We used simulated data to study the effect of using different photo-z estimators to assign galaxies to redshift bins in order to compare their effects on angular clustering and galaxy bias measurements. We found that if we use the entire PDF, rather than a single-point (mean or mode) estimate, the deviations are less biased, especially when using narrow redshift bins. When the redshift bin widths are $\Delta z=0.1$, the use of the entire PDF reduces the typical measurement bias from 5%, when using single point estimates, to 3%., Comment: Matches the MNRAS published version. 19 pages, 19 Figures

We study the implications of Planck data for models of dark energy (DE) and modified gravity (MG) beyond the standard cosmological constant scenario. We start with cases where the DE only directly affects the background evolution, considering Taylor expansions of the equation of state w(a), as well as principal component analysis and parameterizations related to the potential of a minimally coupled DE scalar field. When estimating the density of DE at early times, we significantly improve present constraints and find that it has to be below ~2% (at 95% confidence) of the critical density, even when forced to play a role for z < 50 only. We then move to general parameterizations of the DE or MG perturbations that encompass both effective field theories and the phenomenology of gravitational potentials in MG models. Lastly, we test a range of specific models, such as k-essence, f(R) theories, and coupled DE. In addition to the latest Planck data, for our main analyses, we use background constraints from baryonic acoustic oscillations, type-Ia supernovae, and local measurements of the Hubble constant. We further show the impact of measurements of the cosmological perturbations, such as redshift-space distortions and weak gravitational lensing. These additional probes are important tools for testing MG models and for breaking degeneracies that are still present in the combination of Planck and background data sets. All results that include only background parameterizations (expansion of the equation of state, early DE, general potentials in minimally-coupled scalar fields or principal component analysis) are in agreement with ΛCDM. When testing models that also change perturbations (even when the background is fixed to ΛCDM), some tensions appear in a few scenarios: the maximum one found is ~2σ for Planck TT+lowP when parameterizing observables related to the gravitational potentials with a chosen time dependence; the tension increases to, at most, 3σ when external data sets are included. It however disappears when including CMB lensing., German Research Foundation (DFG), Swiss National Science Foundation (SNSF), European Space Agency, Centre National D'etudes Spatiales, CNRS/INSU-IN2P3-INP (France), Italian Space Agency (ASI), Italian National Research Council, Istituto Nazionale Astrofisica (INAF), National Aeronautics & Space Administration (NASA), United States Department of Energy (DOE), UKSA (UK), Consejo Superior de Investigaciones Cientificas (CSIC), MINECO (Spain), JA (Spain), RES (Spain), Finnish Funding Agency for Technology & Innovation (TEKES), AoF (Finland), CSC (Finland), Helmholtz Association, German Aerospace Centre (DLR), Max Planck Society, CSA (Canada), DTU Space (Denmark), SER/SSO (Switzerland), RCN (Norway), Science Foundation Ireland, Portuguese Foundation for Science and Technology, ERC (EU), European Union (EU), Science & Technology Facilities Council (STFC) ST/J005673/1 ST/M007065/1 ST/M00418X/1 ST/L000393/1 ST/L000768/1 ST/K00333X/1

Cosmic voids are promising tools for cosmological tests due to their sensitivity to dark energy, modified gravity and alternative cosmological scenarios. Most previous studies in the literature of void properties use cosmological N-body simulations of dark matter (DM) particles that ignore the potential effect of baryonic physics. Using a spherical underdensity finder, we analyse voids using the mass field and subhalo tracers in the EAGLE simulations, which follow the evolution of galaxies in a $\rm{\Lambda}$ cold dark matter Universe with state-of-the-art subgrid models for baryonic processes in a $(100 \rm{cMpc})^3$ volume. We study the effect of baryons on void statistics by comparing results with DM-only simulations that use the same initial conditions as EAGLE. When identifying voids in the mass field, we find that a DM-only simulation produces 24 per cent more voids than a hydrodynamical one due to the action of galaxy feedback polluting void regions with hot gas, specially for small voids with $r_{\rm{void}} \le 10\ \rm{Mpc}$. We find that the way in which galaxy tracers are selected has a strong impact on the inferred void properties. Voids identified using galaxies selected by their stellar mass are larger and have cuspier density profiles than those identified by galaxies selected by their total mass. Overall, baryons have minimal effects on void statistics, as void properties are well captured by DM-only simulations, but it is important to account for how galaxies populate DM haloes to estimate the observational effect of different cosmological models on the statistics of voids., Comment: Accepted for publication in MNRAS, 21 pages, 16 figures

The observed 21-cm signal from the epoch of reionization will be distorted along the line-of-sight by the peculiar velocities of matter particles. These redshift-space distortions will affect the contrast in the signal and will also make it anisotropic. This anisotropy contains information about the cross-correlation between the matter density field and the neutral hydrogen field, and could thus potentially be used to extract information about the sources of reionization. In this paper, we study a collection of simulated reionization scenarios assuming different models for the sources of reionization. We show that the 21-cm anisotropy is best measured by the quadrupole moment of the power spectrum. We find that, unless the properties of the reionization sources are extreme in some way, the quadrupole moment evolves very predictably as a function of global neutral fraction. This predictability implies that redshift-space distortions are not a very sensitive tool for distinguishing between reionization sources. However, the quadrupole moment can be used as a model-independent probe for constraining the reionization history. We show that such measurements can be done to some extent by first-generation instruments such as LOFAR, while the SKA should be able to measure the reionization history using the quadrupole moment of the power spectrum to great accuracy., Comment: 17 pages, 12 figures, 1 table. Accepted for publication in MNRAS. Replaced to match the accepted version

The line-of-sight direction in the redshifted 21-cm signal coming from the cosmic dawn and the epoch of reionization is quite unique in many ways compared to any other cosmological signal. Different unique effects, such as the evolution history of the signal, non-linear peculiar velocities of the matter etc. will imprint their signature along the line-of-sight axis of the observed signal. One of the major goals of the future SKA-LOW radio interferometer is to observe the cosmic dawn and the epoch of reionization through this 21-cm signal. It is thus important to understand how these various effects affect the signal for its actual detection and proper interpretation. For more than one and half decades, various groups in India have been actively trying to understand and quantify the different line-of-sight effects that are present in this signal through analytical models and simulations. In many ways the importance of this sub-field under 21-cm cosmology have been identified, highlighted and pushed forward by the Indian community. In this article, we briefly describe their contribution and implication of these effects in the context of the future surveys of the cosmic dawn and the epoch of reionization that will be conducted by the SKA-LOW.

We investigate the expected cosmological constraints from a combination of weak lensing and large-scale galaxy clustering using realistic redshift distributions. Introducing a systematic bias in the weak lensing redshift distributions (of 0.05 in redshift) produces a $>2\sigma$ bias in the recovered matter power spectrum amplitude and dark energy equation of state, for preliminary Stage III surveys. We demonstrate that these cosmological errors can be largely removed by marginalising over unknown biases in the assumed weak lensing redshift distributions, if we assume high quality redshift information for the galaxy clustering sample. Furthermore the cosmological constraining power is mostly retained despite removing much of the information on the weak lensing redshift distribution biases. We show that this comes from complementary degeneracy directions between cosmic shear and the combination of galaxy clustering with cross-correlation between shear and galaxy number density. Finally we examine how the self-calibration performs when the assumed distributions differ from the true distributions by more than a simple uniform bias. We find that the effectiveness of this self-calibration method will depend on the details of a given experiment and the nature of the uncertainties on the estimated redshift distributions., Comment: 6 pages, 6 figures

Standard big bang cosmology predicts a cosmic neutrino background at $T_\nu \simeq 1.95~$K. Given the current neutrino oscillation measurements, we know most neutrinos move at large, but non-relativistic, velocities. Therefore, dark matter haloes moving in the sea of primordial neutrinos form a neutrino wake behind them, which would slow them down, due to the effect of {\it dynamical friction}. In this paper, we quantify this effect for realistic haloes, in the context of the halo model of structure formation, and show that it scales as $m_\nu^4$ $\times$ relative velocity, and monotonically grows with the halo mass. Galaxy redshift surveys can be sensitive to this effect (at $>3\sigma$ confidence level, depending on survey properties, neutrino mass and hierarchy) through redshift space distortions (RSD) of distinct galaxy populations., Comment: 12 pages, 15 figures

We implement an adaptation of the COLA approach, a hybrid scheme that combines Lagrangian perturbation theory with an N-body approach, to model non-linear collapse in chameleon and symmetron modified gravity models. Gravitational screening is modeled effectively through the attachment of a suppression factor to the linearized Klein-Gordon equations. The adapted COLA approach is benchmarked, with respect to an N-body code both for the $\Lambda$CDM scenario and for the modified gravity theories. It is found to perform well in the estimation of the dark matter power spectra, with consistency of 1 % to $k\sim2.5$ h/Mpc. Redshift space distortions are shown to be effectively modeled through a Lorentzian parameterization with a velocity dispersion fit to the data. We find that COLA performs less well in predicting the halo mass functions, but has consistency, within $1\sigma$ uncertainties of our simulations, in the relative changes to the mass function induced by the modified gravity models relative to $\Lambda$CDM. The results demonstrate that COLA, proposed to enable accurate and efficient, non-linear predictions for $\Lambda$CDM, can be effectively applied to a wider set of cosmological scenarios, with intriguing properties, for which clustering behavior needs to be understood for upcoming surveys such as LSST, DESI, Euclid and WFIRST., Comment: 15 pages, 9 figures. Updated to match version published in PRD

We present a non-parametric model for inferring the three-dimensional (3D) distribution of dust density in the Milky Way. Our approach uses the extinction measured towards stars at different locations in the Galaxy at approximately known distances. Each extinction measurement is proportional to the integrated dust density along its line-of-sight. Making simple assumptions about the spatial correlation of the dust density, we can infer the most probable 3D distribution of dust across the entire observed region, including along sight lines which were not observed. This is possible because our model employs a Gaussian Process to connect all lines-of-sight. We demonstrate the capability of our model to capture detailed dust density variations using mock data as well as simulated data from the Gaia Universe Model Snapshot. We then apply our method to a sample of giant stars observed by APOGEE and Kepler to construct a 3D dust map over a small region of the Galaxy. Due to our smoothness constraint and its isotropy, we provide one of the first maps which does not show the "fingers of god" effect., Comment: Minor changes applied. Final version accepted for publication in A&A. 15 pages, 17 figures

We present a direct approach to nonparametrically reconstruct the linear density field from an observed nonlinear map. We solve for the unique displacement potential consistent with the nonlinear density and positive definite coordinate transformation using a multigrid algorithm. We show that we recover the linear initial conditions up to the nonlinear scale ($r_{\delta_r\delta_L}>0.5$ for $k\lesssim1\ h/\mathrm{Mpc}$) with minimal computational cost. This reconstruction approach generalizes the linear displacement theory to fully nonlinear fields, potentially substantially expanding the baryon acoustic oscillations and redshift space distortions information content of dense large scale structure surveys, including for example SDSS main sample and 21cm intensity mapping initiatives., Comment: 7 pages, 7 figures, published version

Recent anomalies found in cosmological datasets such as the low multipoles of the Cosmic Microwave Background or the low redshift amplitude and growth of clustering measured by e.g., abundance of galaxy clusters and redshift space distortions in galaxy surveys, have motivated explorations of models beyond standard $\Lambda$CDM. Of particular interest are models where general relativity (GR) is modified on large cosmological scales. Here we consider deviations from $\Lambda$CDM+GR within the context of Horndeski gravity, which is the most general theory of gravity with second derivatives in the equations of motion. We adopt a parametrization in which the four additional Horndeski functions of time $\alpha_i(t)$ are proportional to the cosmological density of dark energy $\Omega_{DE}(t)$. Constraints on this extended parameter space using a suite of state-of-the art cosmological observations are presented for the first time. Although the theory is able to accommodate the low multipoles of the Cosmic Microwave Background and the low amplitude of fluctuations from redshift space distortions, we find no significant tension with $\Lambda$CDM+GR when performing a global fit to recent cosmological data and thus there is no evidence against $\Lambda$CDM+GR from an analysis of the value of the Bayesian evidence ratio of the modified gravity models with respect to $\Lambda$CDM, despite introducing extra parameters. The posterior distribution of these extra parameters that we derive return strong constraints on any possible deviations from $\Lambda$CDM+GR in the context of Horndeski gravity. We illustrate how our results can be applied to a more general frameworks of modified gravity models., Comment: 22 pages; 4 figures; 9 tables. The constraints have been revised to match the precision required according to the recently released hi_class paper

We describe the Bayesian BARCODE formalism that has been designed towards the reconstruction of the Cosmic Web in a given volume on the basis of the sampled galaxy cluster distribution. Based on the realization that the massive compact clusters are responsible for the major share of the large scale tidal force field shaping the anisotropic and in particular filamentary features in the Cosmic Web. Given the nonlinearity of the constraints imposed by the cluster configurations, we resort to a state-of-the-art constrained reconstruction technique to find a proper statistically sampled realization of the original initial density and velocity field in the same cosmic region. Ultimately, the subsequent gravitational evolution of these initial conditions towards the implied Cosmic Web configuration can be followed on the basis of a proper analytical model or an N-body computer simulation. The BARCODE formalism includes an implicit treatment for redshift space distortions. This enables a direct reconstruction on the basis of observational data, without the need for a correction of redshift space artifacts. In this contribution we provide a general overview of the the Cosmic Web connection with clusters and a description of the Bayesian BARCODE formalism. We conclude with a presentation of its successful workings with respect to test runs based on a simulated large scale matter distribution, in physical space as well as in redshift space., Comment: 18 pages, 8 figures, Proceedings of IAU Symposium 308 "The Zeldovich Universe: Genesis and Growth of the Cosmic Web", 23-28 June 2014, Tallinn, Estonia

This paper presents cosmological results based on full-mission Planck observations of temperature and polarization anisotropies of the cosmic microwave background (CMB) radiation. Our results are in very good agreement with the 2013 analysis of the Planck nominal-mission temperature data, but with increased precision. The temperature and polarization power spectra are consistent with the standard spatially-flat 6-parameter ΛCDM cosmology with a power-law spectrum of adiabatic scalar perturbations (denoted “base ΛCDM” in this paper). From the Planck temperature data combined with Planck lensing, for this cosmology we find a Hubble constant, H0 = (67.8 ± 0.9) km s-1Mpc-1, a matter density parameter Ωm = 0.308 ± 0.012, and a tilted scalar spectral index with ns = 0.968 ± 0.006, consistent with the 2013 analysis. Note that in this abstract we quote 68% confidence limits on measured parameters and 95% upper limits on other parameters. We present the first results of polarization measurements with the Low Frequency Instrument at large angular scales. Combined with the Planck temperature and lensing data, these measurements give a reionization optical depth of τ = 0.066 ± 0.016, corresponding to a reionization redshift of . These results are consistent with those from WMAP polarization measurements cleaned for dust emission using 353-GHz polarization maps from the High Frequency Instrument. We find no evidence for any departure from base ΛCDM in the neutrino sector of the theory; for example, combining Planck observations with other astrophysical data we find Neff = 3.15 ± 0.23 for the effective number of relativistic degrees of freedom, consistent with the value Neff = 3.046 of the Standard Model of particle physics. The sum of neutrino masses is constrained to ∑ mν < 0.23 eV. The spatial curvature of our Universe is found to be very close to zero, with | ΩK | < 0.005. Adding a tensor component as a single-parameter extension to base ΛCDM we find an upper limit on the tensor-to-scalar ratio of r0.002< 0.11, consistent with the Planck 2013 results and consistent with the B-mode polarization constraints from a joint analysis of BICEP2, Keck Array, and Planck (BKP) data. Adding the BKP B-mode data to our analysis leads to a tighter constraint of r0.002 < 0.09 and disfavours inflationarymodels with a V(φ) ∝ φ2 potential. The addition of Planck polarization data leads to strong constraints on deviations from a purely adiabatic spectrum of fluctuations. We find no evidence for any contribution from isocurvature perturbations or from cosmic defects. Combining Planck data with other astrophysical data, including Type Ia supernovae, the equation of state of dark energy is constrained to w = −1.006 ± 0.045, consistent with the expected value for a cosmological constant. The standard big bang nucleosynthesis predictions for the helium and deuterium abundances for the best-fit Planck base ΛCDM cosmology are in excellent agreement with observations. We also constraints on annihilating dark matter and on possible deviations from the standard recombination history. In neither case do we find no evidence for new physics. The Planck results for base ΛCDM are in good agreement with baryon acoustic oscillation data and with the JLA sample of Type Ia supernovae. However, as in the 2013 analysis, the amplitude of the fluctuation spectrum is found to be higher than inferred from some analyses of rich cluster counts and weak gravitational lensing. We show that these tensions cannot easily be resolved with simple modifications of the base ΛCDM cosmology. Apart from these tensions, the base ΛCDM cosmology provides an excellent description of the Planck CMB observations and many other astrophysical data sets., European Space Agency, Centre National D'etudes Spatiales, CNRS/INSU-IN2P3-INP (France), Italian Space Agency (ASI), Italian National Research Council, Istituto Nazionale Astrofisica (INAF), National Aeronautics & Space Administration (NASA), United States Department of Energy (DOE), Science & Technology Facilities Council (STFC), UKSA (UK), Consejo Superior de Investigaciones Cientificas (CSIC), MINECO (Spain), JA (Spain), RES (Spain), Finnish Funding Agency for Technology & Innovation (TEKES), AoF (Finland), CSC (Finland), Helmholtz Association, German Aerospace Centre (DLR), Max Planck Society, CSA (Canada), DTU Space (Denmark), SER/SSO (Switzerland), RCN (Norway), Science Foundation Ireland, Portuguese Foundation for Science and Technology, European Union (EU), European Research Council (ERC) 616170, Science & Technology Facilities Council (STFC) ST/L000652/1, UK BIS National E-infrastructure capital grants, Science & Technology Facilities Council (STFC) ST/L000652/1 ST/M007065/1 ST/J005673/1 ST/K00333X/1 ST/M00418X/1 ST/L000768/1 ST/L000393/1

We investigate a phenomenological non-gravitational coupling between dark energy and dark matter, where the interaction in the dark sector is parameterized as an energy transfer either from dark matter to dark energy or the opposite. The models are constrained by a whole host of updated cosmological data: cosmic microwave background temperature anisotropies and polarization, high-redshift supernovae, baryon acoustic oscillations, redshift space distortions and gravitational lensing. Both models are found to be compatible with all cosmological observables, but in the case where dark matter decays into dark energy, the tension with the independent determinations of $H_0$ and $\sigma_8$, already present for standard cosmology, increases: this model in fact predicts lower $H_0$ and higher $\sigma_8$, mostly as a consequence of the higher amount of dark matter at early times, leading to a stronger clustering during the evolution. Instead, when dark matter is fed by dark energy, the reconstructed values of $H_0$ and $\sigma_8$ nicely agree with their local determinations, with a full reconciliation between high- and low-redshift observations. A non-zero coupling between dark energy and dark matter, with an energy flow from the former to the latter, appears therefore to be in better agreement with cosmological data., Comment: 21 pages, 8 figures, 6 tables, accepted by JCAP

The EoR 21-cm signal is expected to become highly non-Gaussian as reionization progresses. This severely affects the error-covariance of the EoR 21-cm power spectrum which is important for predicting the prospects of a detection with ongoing and future experiments. Most earlier works have assumed that the EoR 21-cm signal is a Gaussian random field where (1) the error variance depends only on the power spectrum and the number of Fourier modes in the particular $k$ bin, and (2) the errors in the different $k$ bins are uncorrelated. Here we use an ensemble of simulated 21-cm maps to analyze the error-covariance at various stages of reionization. We find that even at the very early stages of reionization ($\bar{x}_{\rm HI} \sim 0.9 $) the error variance significantly exceeds the Gaussian predictions at small length-scales ($k > 0.5 \,{\rm Mpc}^{-1}$) while they are consistent at larger scales. The errors in most $k$ bins (both large and small scales), are however found to be correlated. Considering the later stages ($\bar{x}_{\rm HI} = 0.15$), the error variance shows an excess in all $k$ bins within $k \ge 0.1 \, {\rm Mpc}^{-1}$, and it is around $200$ times larger than the Gaussian prediction at $k \sim 1 \, {\rm Mpc}^{-1}$. The errors in the different $k$ bins are all also highly correlated, barring the two smallest $k$ bins which are anti-correlated with the other bins. Our results imply that the predictions for different 21-cm experiments based on the Gaussian assumption underestimate the errors, and it is necessary to incorporate the non-Gaussianity for more realistic predictions., Published in Monthly Notices of the Royal Astronomical Society (MNRAS). Available at "this URL http://dx.doi.org/10.1093/mnras/stw2599"

We study how to recover the full 3D clustering information of P(\vec{k},z), including redshift space distortions (RSD), from 2D tomography using the angular auto and cross spectra of different redshift bins C_\ell(z,z'). We focus on quasilinear scales where the minimum scale \lambda_{min} or corresponding maximum wavenumber k_{max}= 2\pi/\lambda_{min} is targeted to be between k_{max}={0.05-0.2} h/Mpc. For spectroscopic surveys, we find that we can recover the full 3D clustering information when the redshift bin width \Delta z used in the 2D tomography is similar to the targeted minimum scale, i.e. \Delta z ~ {0.6-0.8} \lambda_{min} H(z)/c which corresponds to \Delta z ~ 0.01-0.05 for z \Delta z and most radial information is intrinsically lost. The remaining information can be recovered from the 2D tomography if we use \Delta z ~ 2\sigma_z. While 3D and 2D analysis are shown here to be equivalent, the advantage of using angular positions and redshifts is that we do not need a fiducial cosmology to convert to 3D coordinates. This avoids assumptions and marginalization over the fiducial model. In addition, it becomes straight forward to combine RSD, clustering and weak lensing in 2D space.

We investigate the ability of state-of-the-art redshift-space distortions models for the galaxy anisotropic two-point correlation function \xi(r_p, \pi), to recover precise and unbiased estimates of the linear growth rate of structure f, when applied to catalogues of galaxies characterised by a realistic bias relation. To this aim, we make use of a set of simulated catalogues at z = 0.1 and z = 1 with different luminosity thresholds, obtained by populating dark-matter haloes from a large N-body simulation using halo occupation prescriptions. We examine the most recent developments in redshift-space distortions modelling, which account for non-linearities on both small and intermediate scales produced respectively by randomised motions in virialised structures and non-linear coupling between the density and velocity fields. We consider the possibility of including the linear component of galaxy bias as a free parameter and directly estimate the growth rate of structure f. Results are compared to those obtained using the standard dispersion model, over different ranges of scales.We find that the model of Taruya et al. (2010), the most sophisticated one considered in this analysis, provides in general the most unbiased estimates of the growth rate of structure, with systematic errors within 4% over a wide range of galaxy populations spanning luminosities between L > L* and L > 3L*. The scale-dependence of galaxy bias plays a role on recovering unbiased estimates of f when fitting quasi non-linear scales. Its effect is particularly severe for most luminous galaxies, for which systematic effects in the modelling might be more difficult to mitigate and have to be further investigated. [...]

We assess the sensitivity of void shapes to the nature of dark energy that was pointed out in recent studies and also investigate whether or not void shapes are useable as an observational probe in galaxy redshift surveys. Our focus is on the evolution of the mean void ellipticity and its underlying physical cause. To this end, we analyse the morphological properties of voids in five sets of cosmological N-body simulations, each with a different nature of dark energy. To address the question of whether galaxy redshift surveys yield sufficiently accurate void morphologies, voids in the dark matter distribution are compared to those in the halo population. Voids are identified using the parameter-free Watershed Void Finder. The effect of redshift distortions is investigated as well. The main conclusions of this study are as follows: (i) the statistically significant sensitivity of voids in the dark matter distribution is confirmed; (ii) the level of clustering as measured by s8(z) is identified as the main cause of differences in the mean void shape ; and (iii) in the halo and/or galaxy distribution, it is practically unfeasible to distinguish at a statistically significant level between the various cosmologies due to the sparsity and spatial bias of the sample.

We use large volume N-body simulations to predict the clustering of dark matter in redshift space in f(R) modified gravity cosmologies. This is the first time that the nonlinear matter and velocity fields have been resolved to such a high level of accuracy over a broad range of scales in this class of models. We find significant deviations from the clustering signal in standard gravity, with an enhanced boost in power on large scales and stronger damping on small scales in the f(R) models compared to GR at redshifts z

We develop a robust Bayesian model to derive peculiar velocities and Fundamental Plane (FP) distances for a subsample of 9000 galaxies from the 6dF Galaxy Survey (6dFGS). These galaxies form the basis of 6dFGSv, the largest and most uniform galaxy peculiar-velocity sample to date. We perform a Bayesian analysis of the data set as a whole, determining cosmological parameters from the peculiar-velocity field (e.g., fitting β and the bulk flow), by comparing to the field predicted from the redshift survey and assuming that the galaxy distribution traces the matter distribution.

Cosmological galaxy surveys aim at mapping the largest volumes to test models with techniques such as cluster abundance, cosmic shear correlations or baryon acoustic oscillations (BAO), which are designed to be independent of galaxy bias. Here we explore an alternative route to constrain cosmology: sampling more moderate volumes with the cross-correlation of photometric and spectroscopic surveys. We consider the angular galaxy-galaxy autocorrelation in narrow redshift bins and its combination with different probes of weak gravitational lensing (WL) and redshift space distortions (RSD). Including the cross-correlation of these surveys improves by factors of a few the constraints on both the dark energy equation of state w(z) and the cosmic growth history, parametrized by \gamma. The additional information comes from using many narrow redshift bins and from galaxy bias, which is measured both with WL probes and RSD, breaking degeneracies that are present when using each method separately. We show forecasts for a joint w(z) and \gamma figure of merit using linear scales over a deep (i

Assuming General Relativity is correct on large-scales, Redshift-Space Distortions (RSDs) and the Integrated Sachs-Wolfe effect (ISW) are both sensitive to the time derivative of the linear growth function. We investigate the extent to which these probes provide complementary or redundant information when they are combined to constrain the evolution of the linear velocity power spectrum, often quantified by the function $f(z)\sigma_8(z)$, where $f$ is the logarithmic derivative of $\sigma_8$ with respect to $(1+z)$. Using a spherical Fourier-Bessel (SFB) expansion for galaxy number counts and a spherical harmonic expansion for the CMB anisotropy, we compute the covariance matrices of the signals for a large galaxy redshift survey combined with a CMB survey like Planck. The SFB basis allows accurate ISW estimates by avoiding the plane-parallel approximation, and it retains RSD information that is otherwise lost when projecting angular clustering onto redshift shells. It also allows straightforward calculations of covariance with the CMB. We find that the correlation between the ISW and RSD signals are low since the probes are sensitive to different modes. For our default surveys, on large scales ($k

We investigate the spatial properties of the large-scale structure of the Universe in the framework of coupled dark energy (cDE) cosmologies. Using the public halo catalogues from the Coupled Dark Energy Cosmological Simulations (codecs) simulations – the largest set of N-body experiments to date for such cosmological scenarios – we estimate the clustering and bias functions of cold dark matter (CDM) haloes, both in real space and redshift space. Moreover, we investigate the effects of the dark energy (DE) coupling on the geometric and dynamic redshift-space distortions, quantifying the difference with respect to the concordance CDM model. At , the spatial properties of CDM haloes in cDE models appear very similar to the CDM case, even if the cDE models are normalized at last scattering in order to be consistent with the latest cosmic microwave background (CMB) data. At higher redshifts, we find that the DE coupling produces a significant scale-dependent suppression of the halo clustering and bias function. This effect, which strongly depends on the coupling strength, is not degenerate with at scales . Moreover, we find that the coupled DE strongly affects both the linear distortion parameter, , and the pairwise peculiar velocity dispersion, . Although the models considered in this work are found to be all in agreement with presently available observational data, the next generation of galaxy surveys will be able to put strong constraints on the level of coupling between DE and CDM exploiting the shape of redshift-space clustering anisotropies.

Comparing measurements of redshift-space distortions (RSDs) with geometrical observations of the expansion of the Universe offers tremendous potential for testing general relativity on very large scales. The basic linear theory of RSDs in the distant-observer limit has been known for 25 years and the effect has been conclusively observed in numerous galaxy surveys. The next generation of galaxy survey will observe many millions of galaxies over volumes of many tens of Gpc 3 . They will provide RSD measurements of such exquisite precision that we will have to carefully analyse and correct for many systematic deviations from this simple picture in order to fully exploit the statistical precision obtained. We review RSD theory and show how ubiquitous RSDs actually are, and then consider a number of potential systematic effects, shamelessly highlighting recent work in which we have been involved. This review ends by looking ahead to the future surveys that will make the next generation of RSD measurements.

For decades, cosmologists have been using galaxies to trace the large-scale distribution of matter. At present, the largest source of systematic uncertainty in this analysis is the challenge of modeling the complex relationship between galaxy redshift and the distribution of dark matter. If all galaxies sat in the centers of halos, there would be minimal Finger-of-God (FoG) effects and a simple relationship between the galaxy and matter distributions. However, many galaxies, even some of the luminous red galaxies (LRGs), do not lie in the centers of halos. Because the galaxy-galaxy lensing is also sensitive to the off-centered galaxies, we show that we can use the lensing measurements to determine the amplitude of this effect and to determine the expected amplitude of FoG effects. We develop an approach for using the lensing data to model how the FoG suppresses the power spectrum amplitudes and show that the current data implies a 30% suppression at wavenumber k=0.2h/Mpc. Our analysis implies that it is important to complement a spectroscopic survey with an imaging survey with sufficient depth and wide field coverage. Joint imaging and spectroscopic surveys allow a robust, unbiased use of the power spectrum amplitude information: it improves the marginalized error of growth rate fg=dln D/dln a by up to a factor of 2 over a wide range of redshifts z

Redshift surveys of galaxies beyond the local Universe (z ≫ 0.1) are opening up new possibilities to understanding the observed acceleration of cosmic expansion, one of the greatest mysteries of modern science. Baryonic Acoustic Oscillations in the galaxy power spectrum (or correlation function), provide us with a standard rod to measure the expansion history H(z). At the same time, redshift-space distortions in the clustering pattern due to galaxy peculiar motions are a measure of the growth rate of structure f(z). The combination of these two quantities, allows us to distinguish whether cosmic acceleration is due to the existence of a "dark energy" in the cosmic budget, or rather requires a modification of General Relativity. These two radically alternative scenarios are degenerate when considering H(z) alone, as yielded, e.g. by the Hubble diagram of Type Ia supernovae. In this short review paper I will mostly concentrate on the latter measurement, whose potential importance in this context has been recently highlighted. Current results are consistent with the simplest GR-based cosmological constant scenario, but error bars are still large. Detailed forecasts show that next-generation deep surveys optimizing the combination of large volumes and good galaxy sampling will be able to use redshift distortions as a key tool to understand the physical origin of cosmic acceleration. Among these, I introduce the newly started VIMOS Public Extragalactic Redshift Survey (VIPERS) at the ESO VLT, which is building at [Formula: see text] a sample comparable to the local 2dFGRS. Expectations from even larger surveys planned from space-borne observatories such as EUCLID will also be mentioned.

Galaxy Redshift surveys provide a three-dimensional map of the Universe. Three distinct processes that encode cosmological information in these maps, are commonly used to constrain models: (i) the comoving power spectrum shape depends on the physical properties of the early Universe, including the physical matter, baryon and neutrino densities, the inflation power spectrum and the degree of Gaussianity of density fluctuations; (ii) we can use the statistical clustering of galaxies as a standard ruler by matching it, or parts of it at different redshifts, and to the Cosmic Microwave Background (CMB); (iii) redshift-space distortions, anisotropic patterns caused by peculiar galaxy velocities, reveal structure growth. Following the design of my talk at the 1st Galileo–Xu Guangqi Meeting, I will use these proceedings to briefly review these experiments.

We suggest a method for extracting important cosmological information from observational data on galaxy proper motions on the celestial sphere. These data can be used to reconstruct the three-dimensional velocities of galaxies relative to the cosmicmicrowave background (peculiar velocities), and to separate the Hubble and peculiar components of the observed redshifts in a large volume for the first time. As a result, it is possible to determine the Hubble constant accurately and independently using the radial velocities of comparatively close galaxies (up to 50 Mpc), and to determine distances to the galaxies and the mass distribution in the neighborhood of the Local group of galaxies. The proposed task may be solved using the future “Millimetron” space radio interferometer.

We show that the dependence of Ly-alpha absorption on environment leads to significant non-gravitational features in the redshift space power-spectrum of Ly-alpha selected galaxies. We derive a physically motivated fitting formula that can be included in clustering analyses, and use this to discuss the predicted features in the Ly-alpha galaxy power-spectrum based on detailed models in which Ly-alpha absorption is influenced by gas infall and/or by strong galactic outflows. We show that power-spectrum measurements could be used to study the astrophysics of the galaxy-IGM connection, and to measure the properties of outflows from star-forming galaxies. Applying the modified redshift space power-spectrum to a Ly-alpha survey with parameters corresponding to the planned Hobby-Eberly Telescope Dark Energy Experiment (HETDEX), we find that the dependence of observed Ly-alpha flux on velocity gradient and ionising background may compromise the ability of Ly-alpha selected galaxy redshift surveys to constrain cosmology using information from the full power-spectrum. This is because the effects of fluctuating ionizing background and velocity gradients effect the shape of the observed power-spectrum in ways that are similar to the shape of the primordial power-spectrum and redshift space distortions respectively. We use the Alcock-Paczynski test to show that without prior knowledge of the details of Ly-alpha absorption in the IGM, the precision of line-of-sight and transverse distance measurements for HETDEX will be ~1.3-1.7%, decreased by a factor of ~1.5-2 relative to the best case precision of ~0.8% available in a traditional galaxy redshift survey. We specify the precision with which modelling of Ly-alpha radiative transfer must be understood in order for HETDEX to achieve distance measurements that are better than 1%.