Search

The Tully–Fisher Relation (TFR) is a well-known empirical relationship between the luminosity of a spiral galaxy and its circular velocity, allowing us to estimate redshift independent distances. Here we use high signal-to-noise H  i 21-cm integrated spectra from the second pilot data release (PDR2, 180 deg2) of the Widefield ASKAP L -band Legacy All-sky Blind surveY (WALLABY). In order to prepare for the full WALLABY survey, we have investigated the TFR in phase 2 of the pilot survey with a further three fields. The data were obtained with wide-field Phased Array Feeds on the Australian Square Kilometre Array Pathfinder (ASKAP) and have an angular resolution of 30 arcsec and a velocity resolution of |$\sim$| 4 km s−1. Galaxy luminosities have been measured from the Wide-field Infrared Survey Explorer , and optical galaxy inclinations from the Dark Energy Camera Legacy Survey. We present TFRs for wavelengths from 0.8 to 3.4  μ m. We examine sources of galaxy inclination data and investigate magnitudes from the DECam Local Volume Exploration Survey and DENIS catalogues and the 4HS target catalogue based on the VISTA Hemisphere Survey. We consider the baryonic TFR. These are all of interest for TFR using the full WALLABY survey of 200 000 galaxies. We demonstrate that WALLABY TFR distances can take their place among state-of-the-art studies of the local velocity field. [ABSTRACT FROM AUTHOR]

Recent evidence supporting reionization ending at redshift |$z \lesssim 6$| includes the rapid redshift evolution of the mean free path, |$\lambda _{\rm mfp}$|⁠ , for Lyman-limit photons through the intergalactic medium (IGM) at |$5\lt z\lt 6$|⁠. Here, we investigate |$\lambda _{\rm mfp}$| predicted by the Sherwood–Relics suite of hybrid radiation hydrodynamical simulations. Simulations with comoving volumes of |$40^{3}\, h^{-3}\rm \, cMpc^{3}$| (⁠|$160^{3}\, h^{-3}\rm \, cMpc^{3}$|⁠), calibrated to match the observed Ly |$\alpha$| forest transmission with a late end to reionization at |$z\lt 6$|⁠ , are consistent with recent |$\lambda _{\rm mfp}$| measurements at |$z\lt 5.9$|⁠ , and are |$1.2\sigma$| (⁠|$1.8\sigma$|⁠) above the highest redshift |$\lambda _{\rm mfp}$| measurement at |$z=5.93$|⁠. The majority of the Lyman-limit opacity at the end of reionization is attributable to highly ionized Ly |$\alpha$| forest absorbers with neutral hydrogen column densities |$N_{\rm HI} \leq 10^{16}$| – |$10^{17}\rm \, cm^{-2}$|⁠. Resolving these systems is critical for capturing the redshift evolution of |$\lambda _{\rm mfp}$| during the final stages of reionization. After reionization completes, overdense gas will reduce |$\lambda _{\rm mfp}$| by up to 20 per cent around haloes with masses |$M_{\rm h}\sim 10^{9}$| – |$10^{11}h^{-1}\, {\rm M}_{\odot }$|⁠ , but during reionization ionized bubbles will instead boost |$\lambda _{\rm mfp}$| around haloes by up to an order of magnitude when the IGM is as much as 90 per cent neutral by volume. This effect will play an important role in the visibility of Ly |$\alpha$| emitting galaxies at |$z\gtrsim 10$| discovered with JWST. [ABSTRACT FROM AUTHOR]

Large-scale structure (LSS) surveys will increasingly provide stringent constraints on our cosmological models. Recently, the density-marked correlation function (MCF) has been introduced, offering an easily computable density-correlation statistic. Simulations have demonstrated that MCFs offer additional, independent constraints on cosmological models beyond the standard two-point correlation (2PCF). In this study, we apply MCFs for the first time to SDSS CMASS data, aiming to investigate the statistical information regarding clustering and anisotropy properties in the Universe and assess the performance of various weighting schemes in MCFs, and finally obtain constraints on Ωm. Upon analyzing the CMASS data, we observe that, by combining different weights (α = [−0.2, 0, 0.2, 0.6]), the MCFs provide a tight and independent constraint on the cosmological parameter Ωm, yielding Ωm = 0.293 ± 0.006 at the 1σ level, which represents a significant reduction in the statistical error by a factor of 3.4 compared to that from 2PCF. Our constraint is consistent with recent findings from the small-scale clustering of BOSS galaxies (Zhai et al. Astronphys. J. 948, 99 (2023)) within the 1σ level. However, we also find that our estimate is lower than the Planck measurements by about 2.6σ, indicating the potential presence of new physics beyond the standard cosmological model if all the systematics are fully corrected. The method outlined in this study can be extended to other surveys and datasets, allowing for the constraint of other cosmological parameters. Additionally, it serves as a valuable tool for forthcoming emulator analysis on the Chinese Space Station Telescope (CSST). [ABSTRACT FROM AUTHOR]

Context. Devising fast and accurate methods of predicting the Lyman-α forest at the field level, avoiding the computational burden of running large-volume cosmological hydrodynamic simulations, is of fundamental importance to quickly generate the massive set of simulations needed by the state-of-the-art galaxy and Lyα forest spectroscopic surveys. Aims. We present an improved analytical model to predict the Lyα forest at the field level in redshift space from the dark matter field, expanding upon the widely used Fluctuating Gunn-Peterson Approximation (FGPA). Instead of assuming a unique universal relation over the whole considered cosmic volume, we introduce a dependence on the cosmic web environment (knots, filaments, sheets, and voids) in the model, thereby effectively accounting for nonlocal bias. Furthermore, we include a detailed treatment of velocity bias in the redshift space distortion modeling, allowing the velocity bias to be cosmic-web-dependent. Methods. We first mapped the dark matter field from real to redshift space through a particle-based relation including velocity bias, depending on the cosmic web classification of the dark matter field in real space. We then formalized an appropriate functional form for our model, building upon the traditional FGPA and including a cutoff and a boosting factor mimicking a threshold and inverse-threshold bias effect, respectively, with model parameters depending on the cosmic web classification in redshift space. Eventually, we fit the coefficients of the model via an efficient Markov chain Monte Carlo scheme. Results. We find evidence for a significant difference between the same model parameters in different environments, suggesting that for the investigated setup the simple standard FGPA is not able to adequately predict the Lyα forest in the different cosmic web regimes. We reproduce the summary statistics of the reference cosmological hydrodynamic simulation that we use for comparison, yielding an accurate mean transmitted flux, probability distribution function, 3D power spectrum, and bispectrum. In particular, we achieve maximum deviation and average deviation accuracy in the Lyα forest 3D power spectrum of ∼3% and ∼0.1% up to k ∼ 0.4 h Mpc−1, and ∼5% and ∼1.8% up to k ∼ 1.4 h Mpc−1. Conclusions. Our new model outperforms previous analytical efforts to predict the Lyα forest at the field level in all the probed summary statistics, and has the potential to become instrumental in the generation of fast accurate mocks for covariance matrices estimation in the context of current and forthcoming Lyα forest surveys. [ABSTRACT FROM AUTHOR]

In this study, we use the merger process of clusters/voids in the role of variable dark energy fluid to alleviate the Hubble tension, which can lead to a balance in the cosmological expansion rate. To reach this target, we will introduce a modified form of energy density for cosmic fluid with the quadratic equation of state, and then we obtain Hubble, deceleration parameters, and luminosity distance for this fluid. To obtain the merger factor and other parameters of our model, we utilize the NONLINEARMODELFIT function within MATHEMATICA. By consideration of the local and global measurements of |$\rm H_0$|⁠ , and the equation of state parameter w as the priory values, and fitting our model with observational Hubble data measurements, we will show that the merger of clusters/voids plays the role of balancing the cosmic expansion rate. Also, it will be shown that the model is more compatible than w CDM with the standard model to describe the accelerating Universe [ABSTRACT FROM AUTHOR]

ABSTRACT: The 21-cm signal from the Cosmic Dawn (CD) is likely to contain large fluctuations, with the most extreme astrophysical models on the verge of being ruled out by observations from radio interferometers. It is therefore vital that we understand not only the astrophysical processes governing this signal, but also other inherent processes impacting the signal itself, and in particular line-of-sight effects. Using our suite of fully numerical radiative transfer simulations, we investigate the impact on the redshifted 21-cm from the CD from one of these processes, namely the redshift-space distortions (RSDs). When RSDs are added, the resulting boost to the power spectra makes the signal more or equally detectable for our models for all redshifts, further strengthening hopes that a power spectra measurement of the CD will be possible. RSDs lead to anisotropy in the signal at the beginning and end of the CD, but not while X-ray heating is underway. The inclusion of RSDs, however, decreases detectability of the non-Gaussianity of fluctuations from inhomogeneous X-ray heating as measured by the skewness and kurtosis. On the other hand, mock observations created from all our simulations that include telescope noise corresponding to 1000 h of observation with the Square Kilometre Array telescope show that we may be able to image the CD for all heating models considered and suggest RSDs dramatically boost fluctuations coming from the inhomogeneous Ly α background.

We evaluate the covariance matrix of the matter power spectrum using perturbation theory up to dominant terms at 1-loop order and compare it to numerical simulations.We decompose the covariance matrix into the disconnected (Gaussian) part, trispectrum from the modes outside the survey (supersample variance) and trispectrum from the modes inside the survey, and show how the different components contribute to the overall covariance matrix. We find the agreement with the simulations is at a 10 per cent level up to k ~ 1 h Mpc-1. We show that all the connected components are dominated by the large-scale modes (k < 0.1 h Mpc-1), regardless of the value of the wave vectors k, k' of the covariance matrix, suggesting that one must be careful in applying the jackknife or bootstrap methods to the covariance matrix. We perform an eigenmode decomposition of the connected part of the covariance matrix, showing that at higher k, it is dominated by a single eigenmode. The full covariance matrix can be approximated as the disconnected part only, with the connected part being treated as an external nuisance parameter with a known scale dependence, and a known prior on its variance for a given survey volume. Finally, we provide a prescription for how to evaluate the covariance matrix from small box simulations without the need to simulate large volumes.

We present measurements of the angular diameter distance to and Hubble parameter at z = 0.57 from the measurement of the baryon acoustic peak in the correlation of galaxies from the Sloan Digital Sky Survey III Baryon Oscillation Spectroscopic Survey. Our analysis is based on asample from Data Release 9 of 264 283 galaxies over 3275 square degrees in the redshift range 0.43 < z < 0.70. We use two different methods to provide robust measurement of the acoustic peak position across and along the line of sight in order to measure the cosmological distance scale. We find DA(0.57) = 1408 ± 45 Mpc and H(0.57) = 92.9 ± 7.8 km s-1 Mpc-1 for our fiducial value of the sound horizon. These results from the anisotropic fitting are fully consistent with the analysis of the spherically averaged acoustic peak position presented in Anderson et al. Our distance measurements are a close match to the predictions of the standard cosmological model featuring a cosmological constant and zero spatial curvature. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Red and blue galaxies are traditionally classified using some specific cuts in colour or other galaxy properties, which are supported by empirical arguments. The vagueness associated with such cuts are likely to introduce a significant contamination in these samples. Fuzzy sets are vague boundary sets that can efficiently capture the classification uncertainty in the absence of any precise boundary. We propose a method for classification of galaxies according to their colours using fuzzy set theory. We use data from the Sloan Digital Sky Survey (SDSS) to construct a fuzzy set for red galaxies with its members having different degrees of 'redness'. We show that the fuzzy sets for the blue and green galaxies can be obtained from it using different fuzzy operations. We also explore the possibility of using fuzzy relation to study the relationship between different galaxy properties and discuss its strengths and limitations. [ABSTRACT FROM AUTHOR]

We present a same-level comparison of the most prominent inversion methods for the reconstruction of the matter density field in the quasi-linear regime from the Ly α forest flux. Moreover, we present a pathway for refining the reconstruction in the framework of numerical optimization. We apply this approach to construct a novel hybrid method. The methods which are used so far for matter reconstructions are the Richardson–Lucy algorithm, an iterative Gauss–Newton method and a statistical approach assuming a one-to-one correspondence between matter and flux. We study these methods for high spectral resolutions such that thermal broadening becomes relevant. The inversion methods are compared on synthetic data (generated with the lognormal approach) with respect to their performance, accuracy, their stability against noise, and their robustness against systematic uncertainties. We conclude that the iterative Gauss–Newton method offers the most accurate reconstruction, in particular at small S / N , but has also the largest numerical complexity and requires the strongest assumptions. The other two algorithms are faster, comparably precise at small noise-levels, and, in the case of the statistical approach, more robust against inaccurate assumptions on the thermal history of the intergalactic medium (IGM). We use these results to refine the statistical approach using regularization. Our new approach has low numerical complexity and makes few assumptions about the history of the IGM, and is shown to be the most accurate reconstruction at small S / N , even if the thermal history of the IGM is not known. Our code will be made publicly available. [ABSTRACT FROM AUTHOR]

The capacity of Stage IV lensing surveys to measure the neutrino mass sum and differentiate between the normal and inverted mass hierarchies depends on the impact of nuisance parameters describing small-scale baryonic astrophysics and intrinsic alignments. For a Euclid-like survey, we perform the first combined weak lensing and galaxy clustering Fisher analysis with baryons, intrinsic alignments, and massive neutrinos for both hierarchies. We use a matter power spectrum generated from a halo model that captures the impact of baryonic feedback and adiabatic contraction. For weak lensing, we find that baryons cause severe degradation to forecasts of the neutrino mass sum, Σ, approximately doubling σΣ. We show that including galaxy clustering constraints from Euclid and BOSS, and cosmic microwave background (CMB) Planck priors, can reduce this degradation to σΣ to 9 per cent and 16 per cent for the normal and inverted hierarchies, respectively. The combined forecasts, |$\sigma _{\Sigma _{\rm {NH}}}=0.034\, \rm {eV}$| and |$\sigma _{\Sigma _{\rm {IH}}}=0.034\, \rm {eV}$|⁠ , preclude a meaningful distinction of the hierarchies but could be improved upon with future CMB priors on ns and information from neutrinoless double beta decay to achieve a 2σ distinction. The effect of intrinsic alignments on forecasts is shown to be minimal, with σΣ even experiencing mild improvements due to information from the intrinsic alignment signal. We find that while adiabatic contraction and intrinsic alignments will require careful calibration to prevent significant biasing of Σ, there is less risk presented by feedback from energetic events like AGN and supernovae. [ABSTRACT FROM AUTHOR]

In the near future galaxy surveys will target Lyman alpha emitting galaxies (LAEs) to unveil the nature of dark energy. It has been suggested that the observability of LAEs is coupled to the large-scale properties of the intergalactic medium. Such coupling could introduce distortions into the observed clustering of LAEs, adding a new potential difficulty to the interpretation of upcoming surveys. We present a model of LAEs that incorporates Ly α radiative transfer processes in the interstellar and intergalactic medium. The model is implemented in the GALFORM semi-analytic model of galaxy of formation and evolution. We find that the radiative transfer inside galaxies produces selection effects over galaxy properties. In particular, observed LAEs tend to have low metallicities and intermediate star formation rates. At low redshift we find no evidence of a correlation between the spatial distribution of LAEs and the intergalactic medium properties. However, at high redshift the LAEs are linked to the line of sight velocity and density gradient of the intergalactic medium. The strength of the coupling depends on the outflow properties of the galaxies and redshift. This effect modifies the clustering of LAEs on large scales, adding non-linear features. In particular, our model predicts modifications to the shape and position of the baryon acoustic oscillation peak. This work highlights the importance of including radiative transfer physics in the cosmological analysis of LAEs. [ABSTRACT FROM AUTHOR]

Baryonic effects on large-scale structure, if not accounted for, can significantly bias dark energy constraints. As the detailed physics of the baryons is not yet well understood, correcting for baryon effects introduces additional parameters which must be marginalized over, increasing the uncertainties on the inferred cosmological parameters. Forthcoming weak lensing surveys are aiming for percent-level precision on the dark energy equation of state, so the problem must be thoroughly examined. We use a halo model with analytic modifications which capture the impact of adiabatic contraction of baryons and feedback on the matter power spectrum, and generalize the Navarro–Frenk–White profile to account for a possible inner core. A Fisher analysis predicts degradations of 40 per cent in the $$w_{ 0}-w_{ a}$$ Figure of Merit for a Euclid-like survey, and up to 80 per cent for other cosmological parameters. We forecast potential inner core constraints of a few kpc, while for a fixed inner core, adiabatic concentration and feedback parameters are constrained to a few per cent. We explore the scales where baryons and dark energy contribute most to the Fisher information, finding that probing to increasingly non-linear scales does little to reduce degradation. Including external baryon information improves our forecasts, but limiting degradation to 1 per cent requires strong priors. Adding Planck cosmic microwave background priors improves the Figure of Merit by a factor of 2.7 and almost completely recovers the individual marginalized errors on $$w$$ 0 and $$w$$ a . We also quantify the calibration of baryon modelling required to reduce biases of dark energy forecasts to acceptable levels for forthcoming lensing surveys. [ABSTRACT FROM AUTHOR]

We compile available constraints on the carbon monoxide (CO) 1-0 luminosity functions and abundances at redshifts 0-3. This is used to develop a data driven halo model for the evolution of the CO galaxy abundances and clustering across intermediate redshifts. It is found that the recent constraints from the CO Power Spectrum Survey (z ~ 3; Keating et al. 2016), when combined with existing observations of local galaxies (z ~ 0; Keres, Yun & Young 2003), lead to predictions that are consistent with the results of smaller surveys at intermediate redshifts (z ~ 1-2). We provide convenient fitting forms for the evolution of the CO luminosity-halo mass relation, and estimates of the mean and uncertainties in the CO power spectrum in the context of future intensity mapping experiments. [ABSTRACT FROM AUTHOR]

We test for reliability any signatures of field galaxies clustering in the GRB021004 line of sight. The first signature is the GRB021004 field photometric redshifts distribution based on the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences observations with a peak near z ~ 0.56 estimated from multicolor photometry in the GRB direction. The second signature is the Mg II λλ2796, 2803 Å absorption doublet at z ≈ 0.56 in VLT/UVES spectra obtained for the GRB021004 afterglow. The third signature is the galaxy clustering in a larger (of about 3° × 3°) area around GRB021004 with an effective peak near z ~ 0.56 for both the spectral and photometric redshifts from a few catalogs of clusters based on the Sloan Digital Sky Survey (SDSS) and Baryon Oscillation Spectroscopic Survey (BOSS) as a part of SDSS-III. From catalog data the size of the whole inhomogeneity in distribution of the galaxy cluster with the peak near z ≈ 0.56 was also estimated as about 6°-8° or 140-190 Mpc. A possibility of inhomogeneity (a galaxy cluster) near the GRB021004 direction can be also confirmed by an inhomogeneity in cosmic microwave background related with the Sunyaev-Zeldovich effect. [ABSTRACT FROM AUTHOR]

Simulations play a vital role in testing and validating HI 21-cm power spectrum estimation techniques. Conventional methods use techniques like N-body simulations to simulate the sky signal which is then passed through a model of the instrument. This makes it necessary to simulate the HI distribution in a large cosmological volume, and incorporate both the lightcone effect and the telescope&'s chromatic response. The computational requirements may be particularly large if one wishes to simulate many realizations of the signal. In this paper, we present an analytical method to simulate the HI visibility signal. This is particularly efficient if one wishes to simulate a large number of realizations of the signal. Our method is based on theoretical predictions of the visibility correlation which incorporate both the light-cone effect and the telescope&'s chromatic response. We have demonstrated this method by applying it to simulate the HI visibility signal for the upcoming Ooty Wide Field Array Phase I. [ABSTRACT FROM AUTHOR]

'Galaxy groups' have hardly been realized as a separate class of objects with specific characteristics in the structural hierarchy. The presumption that the self-similarity of dark matter structures is a valid prescription for the baryonic universe at all scales has rendered smaller structures undetectable by current observational facilities, leading to lesser dedicated studies on them. Some recent reports that indicate a deviation from LX-T scaling in groups compared to clusters have motivated us to study their physical properties in depth. In this article, we report the extensive study on physical properties of groups in comparison to the clusters through cosmological hydrodynamic plus N-body simulations using ENZO 2.2 code. As additional physics, radiative cooling, heating due to supernova and star motions, star formation and stellar feedback have been implemented. We have produced a mock sample of 362 objects with mass ranging from 5 × 1012 Mʘ to 2.5 ×1015 Mʘ. Strikingly, we have found that objects with mass below ~8 × 1013 Mʘ do not follow any of the cluster self-similar laws in hydrostatics, not even in thermal and non-thermal energies. Two distinct scaling laws are observed to be followed with breaks at ~8 × 1013 Mʘ for mass, ~1 keV for temperature and ~1 Mpc for radius. This places groups as a distinct entity in the hierarchical structures, well demarcated from clusters. This study reveals that groups are mostly far away from virialization, suggesting the need for formulating new models for deciphering their physical parameters. They are also shown to have high turbulence and more non-thermal energy stored, indicating better visibility in the non-thermal regime. [ABSTRACT FROM AUTHOR]

We study, by means of a spherical collapse model, the effect of shear, rotation, and baryons on a generalized Chaplygin gas (gCg) dominated universes. We show that shear, rotation, and the baryon presence slow down the collapse with respect to the simple spherical collapse model. The slowing down in the growth of density perturbation is able to solve the instability of the unified dark matter (UDM) models described in previous papers (e.g., Sandvik et al. 2004) at the linear perturbation level, as also shown by a direct comparison of our model with previous results. [ABSTRACT FROM AUTHOR]

We use information entropy to analyse the anisotropy in the mock galaxy catalogues from dark matter distribution and simulated biased galaxy distributions from Ʌ cold dark matter N-body simulation. We show that one can recover the linear bias parameter of the simulated galaxy distributions by comparing the radial, polar and azimuthal anisotropies in the simulated galaxy distributions with that from the dark matter distribution. This method for determination of the linear bias requires only O(N) operations as compared to O(N2) or at least O(NlogN) operations required for the methods based on the two-point correlation function and the power spectrum. We apply this method to determine the linear bias parameter for the galaxies in the 2MASS Redshift Survey (2MRS) and find that the 2MRS galaxies in the Ks band have a linear bias of ~1.3 [ABSTRACT FROM AUTHOR]

We analyse the clustering of cosmic voids using a numerical simulation and the main galaxy sample from the Sloan Digital Sky Survey.We take into account the classification of voids into two types that resemble different evolutionary modes: those with a rising integrated density profile (void-in-void mode or R-type) and voids with shells (void-in-cloud mode or S-type). The results show that voids of the same type have stronger clustering than the full sample. We use the correlation analysis to define void clumps, associations with at least two voids separated by a distance of at most the mean void separation. In order to study the spatial configuration of void clumps, we compute the minimal spanning tree and analyse their multiplicity, maximum length and elongation parameter. We further study the dynamics of the smaller sphere that enclose all the voids in each clump. Although the global densities of void clumps are different according to their member-void types, the bulk motions of these spheres are remarkably lower than those of randomly placed spheres with the same radius distribution. In addition, the coherence of pairwise void motions does not strongly depend on whether voids belong to the same clump. Void clumps are useful to analyse the large-scale flows around voids, since voids embedded in large underdense regions are mostly in the void-in-void regime, where the expansion of the larger region produces the separation of voids. Similarly, voids around overdense regions form clumps that are in collapse, as reflected in the relative velocities of voids that are mostly approaching. [ABSTRACT FROM AUTHOR]

We study the main cosmological properties of the agegraphic dark energy model at the expansion and perturbation levels. Initially, using the latest cosmological data, we implement a joint likelihood analysis in order to constrain the cosmological parameters. Then, we test the performance of the agegraphic dark energy model at the perturbation level and we define its difference from the usual Lambda cold dark matter (CDM) model. Within this context, we verify that the growth index of matter fluctuations depends on the choice of the considered agegraphic dark energy (homogeneous or clustered). In particular, assuming a homogeneous age graphic dark energy, we find, for the first time, that the asymptotic value of the growth index is γ ≈ 5/9, which is close to that of the usual cosmology, γ(A) ≈ 6/11. Finally, if the distribution of dark energy is clustered, then we obtain γ ≈ 1/2 which is ~8 per cent smaller than that of the CDM model. [ABSTRACT FROM AUTHOR]

Alarge fraction of the baryonic matter in the Universe is located in filaments in the intergalactic medium (IGM). However, the low surface brightness of these filaments has not yet allowed their direct detection except in very special regions in the circum-galactic medium. Here we simulate the intensity and spatial fluctuations in Lyman alpha (Lyα) emission from filaments in the IGM and discuss the prospects for the next generation of space-based instruments to detect the low-surface brightness Universe at ultraviolet (UV) wavelengths. Starting with a highresolution N-body simulation, we obtain the dark matter density fluctuations and associate baryons with the dark matter particles assuming that they follow the same spatial distribution. The IGM thermal and ionization state is set by a model of the UV background and by the relevant cooling processes for a hydrogen and helium gas. The Lyα emissivity is then estimated, taking into account recombination and collisional excitation processes. We find that the detection of these filaments through their Lya emission is well in the reach of the next generation of UV space-based instruments and so it should be achieved in the next decade. The density field is populated with halos and galaxies and their Lyα emission is estimated. Galaxies are treated as foregrounds and so we discuss methods to reduce their contamination from observational maps. Finally, we estimate the UV continuum background as a function of the redshift of the Lyα emission line and discuss how this continuum can affect observations. [ABSTRACT FROM AUTHOR]

Observations of the neutral hydrogen (H I) 21-cm signal hold the potential of allowing us to map out the cosmological large-scale structures (LSS) across the entire post-reionization era (z ≤ 6). Several experiments are planned to map the LSS over a large range of redshifts and angular scales, many of these targeting the Baryon Acoustic Oscillations. It is important to model the HI distribution in order to correctly predict the expected signal, and more so to correctly interpret the results after the signal is detected. In this paper we have carried out semi-numerical simulations to model the HI distribution and study the HI power spectrum PHI(k, z) across the redshift range 1 ≤ z ≤ 6. We have modelled the HI bias as a complex quantity ?b(k, z) whose modulus squared b²(k, z) relates PHI(k, z) to the matter power spectrum P(k, z), and whose real part br(k, z) quantifies the cross-correlation between the HI and the matter distribution. We study the z and k dependence of the bias, and present polynomial fits which can be used to predict the bias across 0 ≤ z ≤ 6 and 0.01 ≤ k ≤ 10 Mpc-1. We also present results for the stochasticity r = br/b which is important for cross-correlation studies. [ABSTRACT FROM AUTHOR]

We demonstrate a new method to constrain gravity on the largest cosmological scales by combining measurements of cosmic microwave background (CMB) lensing and the galaxy velocity field. EG is a statistic, constructed from a gravitational lensing tracer and a measure of velocities such as redshift-space distortions (RSD), that can discriminate between gravity models while being independent of clustering bias and σ8. While traditionally, the lensing field for EG has been probed through galaxy lensing, CMB lensing has been proposed as a more robust tracer of the lensing field for EG at higher redshifts while avoiding intrinsic alignments. We perform the largest-scale measurement of EG ever, up to 150 Mpc h-1, by cross-correlating the PlanckCMBlensing map with the Sloan Digital Sky Survey III (SDSS-III) CMASS galaxy sample and combining this with our measurement of the CMASS auto-power spectrum and the RSD parameter β. We report EG(z = 0.57) = 0.243 ± 0.060 (stat) ± 0.013 (sys), a measurement in tension with the general relativity (GR) prediction at a level of 2.6σ. Note that our EG measurement deviates from GR only at scales greater than 80 Mpc h-1, scales which have not been probed by previous EG tests. Upcoming surveys, which will provide an order-of-magnitude reduction in statistical errors, can significantly constrain alternative gravity models when combined with better control of systematics. [ABSTRACT FROM AUTHOR]

We present a series of results from a clustering analysis of the first data release of the Visible and Infrared Survey Telescope for Astronomy (VISTA) Deep Extragalactic Observations (VIDEO) survey. VIDEO is the only survey currently capable of probing the bulk of stellar mass in galaxies at redshifts corresponding to the peak of star formation on degree scales. Galaxy clustering is measured with the two-point correlation function, which is calculated using a non-parametric kernel-based density estimator.We use our measurements to investigate the connection between the galaxies and the host dark matter halo using a halo occupation distribution methodology, deriving bias, satellite fractions, and typical host halo masses for stellar masses between 109.35 and 1010.85M☉, at redshifts 0.5 < z < 1.7. Our results show typical halo mass increasing with stellar mass (with moderate scatter) and bias increasing with stellar mass and redshift consistent with previous studies. We find that the satellite fraction increased towards low redshifts, from ∼5 per cent at z ∼ 1.5 to ∼20 per cent at z ∼ 0.6. We combine our results to derive the stellar mass-to-halo mass ratio for both satellites and centrals over a range of halo masses and find the peak corresponding to the halo mass with maximum star formation efficiency to be ∼2 × 1012M☉, finding no evidence for evolution. [ABSTRACT FROM AUTHOR]

We present an accurate non-linear matter power spectrum prediction scheme for a variety of extensions to the standard cosmological paradigm, which uses the tuned halo model previously developed in Mead et al. We consider dark energy models that are both minimally and non-minimally coupled, massive neutrinos and modified gravitational forces with chameleon and Vainshtein screening mechanisms. In all cases, we compare halo-model power spectra to measurements from high-resolution simulations. We show that the tuned halo-model method can predict the non-linear matter power spectrum measured from simulations of parametrized w(a) dark energy models at the few per cent level for k < 10h Mpc-1, and we present theoretically motivated extensions to cover non-minimally coupled scalar fields, massive neutrinos and Vainshtein screened modified gravity models that result in few per cent accurate power spectra for k < 10 h Mpc-1. For chameleon screened models, we achieve only 10 per cent accuracy for the same range of scales. Finally, we use our halo model to investigate degeneracies between different extensions to the standard cosmological model, finding that the impact of baryonic feedback on the non-linear matter power spectrum can be considered independently of modified gravity or massive neutrino extensions. In contrast, considering the impact of modified gravity and massive neutrinos independently results in biased estimates of power at the level of 5 per cent at scales k > 0.5 h Mpc-1. An updated version of our publicly available HMCODE can be found at https://github.com/alexander-mead/hmcode. [ABSTRACT FROM AUTHOR]

In this work, we investigate the impact of cosmic flows and density perturbations on Hubble constantH0 measurements using non-linear phase-space reconstructions of the Local Universe (LU). In particular, we rely on a set of 25 precise constrained N-body simulations based on Bayesian initial conditions reconstructions of the LU using the Two-Micron Redshift Survey galaxy sample within distances of about 90 h-1 Mpc. These have been randomly extended up to volumes enclosing distances of 360 h-1 Mpc with augmented Lagrangian perturbation theory (750 simulations in total), accounting in this way for gravitational mode coupling from larger scales, correcting for periodic boundary effects, and estimating systematics of missing attractors (slarge = 134 s-1 km).We report on Local Group (LG) speed reconstructions, which for the first time are compatible with those derived from cosmic microwave background-dipole measurements: |νLG| = 685 ± 137 s-1 km. The direction (l, b) = (260.°5 ± 13.°3, 39.°1 ± 10.°4) is found to be compatible with the observations after considering the variance of large scales. Considering this effect of large scales, our local bulk flow estimations assuming a ʌ cold dark matter model are compatible with the most recent estimates based on velocity data derived from the Tully-Fisher relation. We focus on low-redshift supernova measurements out to 0.01 < z<0.025, which have been found to disagree with probes at larger distances. Our analysis indicates that there are two effects related to cosmic variance contributing to this tension. The first one is caused by the anisotropic distribution of supernovae, which aligns with the velocity dipole and hence induces a systematic boost in H0. The second one is due to the inhomogeneous matter fluctuations in the LU. In particular, a divergent region surrounding the Virgo Supercluster is responsible for an additional positive bias in H0. Taking these effects into account yields a correction of ΔH0 = -1.76 ± 0.21 s-1 km Mpc-1, thereby reducing the tension between local probes and more distant probes. Effectively H0 is lower by about 2 per cent. [ABSTRACT FROM AUTHOR]

We analyse a set of volume-limited samples from SDSS DR12 to quantify the degree of inhomogeneity at different length-scales using Shannon entropy. We find that the galaxy distributions exhibit a higher degree of inhomogeneity as compared to a Poisson point process at all length-scales. Our analysis indicates that signatures of inhomogeneities in the galaxy distributions persist at least up to a length-scale of 120 h-1 Mpc. The galaxy distributions appear to be homogeneous on a scale of 140 h-1 Mpc and beyond. Analysing a set of mock galaxy samples from a semi-analytic galaxy catalogue from the Millennium simulation, we find a scale of transition to homogeneity at ~100 h-1 Mpc. [ABSTRACT FROM AUTHOR]

It is shown here that in a flat, cold dark matter (CDM)-dominated Universe with positive cosmological constant (?), modelled in terms of a Newtonian and collisionless fluid, particle trajectories are analytical in time (representable by a convergent Taylor series) until at least a finite time after decoupling. The time variable used for this statement is the cosmic scale factor, i.e. the 'a-time', and not the cosmic time. For this, a Lagrangian-coordinate formulation of the Euler-Poisson equations is employed, originally used by Cauchy for 3D incompressible flow. Temporal analyticity for ?CDM is found to be a consequence of novel explicit all-order recursion relations for the a-time Taylor coefficients of the Lagrangian displacement field, from which we derive the convergence of the a-time Taylor series. A lower bound for the a-time where analyticity is guaranteed and shell-crossing is ruled out is obtained, whose value depends only on ? and on the initial spatial smoothness of the density field. The largest time interval is achieved when ? vanishes, i.e. for an Einstein-de Sitter universe. Analyticity holds also if, instead of the a-time, one uses the linear structure growth D-time, but no simple recursion relations are then obtained. The analyticity result also holds when a curvature term is included in the Friedmann equation for the background, but inclusion of a radiation term arising from the primordial era spoils analyticity. [ABSTRACT FROM AUTHOR]

We present a novel way of using neural networks (NN) to estimate the redshift distribution of a galaxy sample. We are able to obtain a probability density function (PDF) for each galaxy using a classification NN. The method is applied to 58 714 galaxies in CFHTLenS that have spectroscopic redshifts from DEEP2, VVDS and VIPERS. Using this data, we show that the stacked PDFs give an excellent representation of the true N(z) using information from 5, 4 or 3 photometric bands. We show that the fractional error due to using N(zphot) instead of N(ztruth) is ≤1 per cent on the lensing power spectrum (Pκ) in several tomographic bins. Further, we investigate how well this method performs when few training samples are available and show that in this regime the NN slightly overestimates the N(z) at high z. Finally, the case where the training sample is not representative of the full data set is investigated. [ABSTRACT FROM AUTHOR]

The statistical translation invariance of cosmological random fields is broken by a finite survey boundary, correlating the observable Fourier modes. Standard methods for generating Gaussian fields either neglect these correlations, or are costly, or both. Here, we report on a fast and exact simulation method applicable to a wide class of two-point statistics that requires the simulation of a periodic grid of only twice the survey side with fast Fourier transforms. Supersurvey modes, dominating the covariance of power spectra beyond linear scales in galaxy surveys and causing the correlation of large and small scales, ‘beat coupling’, or ‘super-sample’ covariance, are precisely accounted for in non-linear transformations of the Gaussian field. As an application, we simulate the CFHTLS (Canada–France–Hawaii Telescope Large Survey) ∼7° × 7° W1 galaxy density field, modelled as a Poisson sampling of a lognormal density field. We show that our simulations produce power spectra, A★-power spectra, counts-in-cells probability distributions as well as covariances perfectly consistent with the data. In addition, our technique reproduces the information plateau beyond linear scales as observed previously in Sloan Digital Sky Survey galaxy catalogues and in N-body simulations. Our method is thus an efficient yet powerful simulation and prediction tool for galaxy survey data and covariances. [ABSTRACT FROM PUBLISHER]

The correlation function theory on the basis of prescribed boundary conditions provides a deeper understanding in studying the dynamical parameters of galaxy clusters. The approach approximates that the moderate dense systems discussed by a two point correlation function is helpful for describing the dynamical nature of galaxy clusters. The projected theory of two point correlation function for point mass and extended mass structures can be used an alternative tool in measuring the average peculiar motion and temperature profile of galaxy clusters. [ABSTRACT FROM AUTHOR]

We present a very detailed analysis of Chandra and XMM- Newton observations of XLSSJ022403.9-041328 galaxy cluster of z=1, which was detected during the XMM-Newton Large Scale Structure survey. To define the 'luminosity-temperature-mass', L- T- M, scaling relations we built temperature, surface brightness, density, and mass profiles. The total gravitational mass of this cluster was taken within the scaled radius, R, was determined under the assumption of hydrostatic equilibrium for intercluster gas and spherical symmetry of a cluster. The temperature of XLSSJ022403.9-041328 was found to be 4.5±0.7 keV from the Chandra data, and 3.8±0.3 from the XMM- Newton data. The total gravitational mass is equal to 1.44±0.23×10 M at the corresponding radius, while the fraction of gas is equal to 15 % of a total mass. These values were used to define the XLSSJ022403.9-041328 galaxy cluster at the L- T- M scaling relations, and for all of these cases we got agreement which fitting well with self-similar model. This research permits us to use L- T- M relations for galaxy clusters at a highest redshift in the cosmological probes. [ABSTRACT FROM AUTHOR]

Recently, Melia and his coworkers have proposed the so-called Rh = ct cosmology where the scale factor of the universe is a(t) ∝ t and the spatial part is flat. Here, we look at this proposal from a fundamental angle. First, we note that Melia cosmology looks strikingly similar to the old Milne cosmology where a(t) ∝ t and the spatial part is negatively curved. It is known that though Milne cosmology is a valid Friedmann solution, it actually corresponds to ρ = 0 and can be described by a globally static Minkowski metric. Secondly, we note that for the Melia model, Ricci & Kretschmann scalars assume their perfect static form hinting that it too may tacitly correspond to vacuum. To compare Melia universe with the Milne universe, we express Melia metric too in curvature/Schwarzschild coordinates. Finally, by using the fact for such coordinate transformations dx′4 = Jdx4, where J is the appropriate Jacobian, we explicitly show that Melia metric is static, which for k = 0 case implies vacuum. This shows that even apparently meaningful general relativistic solutions could be illusory as far as physical reality is concerned. And since Melia model is the unique solution for the big bang model, eventually, all big bang models could be mathematical illusions. [ABSTRACT FROM AUTHOR]

The general problem of the statistics of the primordial curvature perturbation field in cosmology is reviewed. The search for non-Gaussian signatures in cosmological perturbations, originated from inflation in the early Universe is discussed both from the theoretical point of view and in connection with constraints coming from recent observations and future prospects for observing/constraining them. [ABSTRACT FROM PUBLISHER]

We study the phase transition in a gravitating system by analyzing grand canonical partition function as a function of complex fugacity. We extend the Yang-Lee theory to study phase transitions in the gravitational galaxy clustering of galaxies having a variety of masses. This generalizes our previous work based on the same theory for the single-component system to a multicomponent system. We find that galaxy clustering is sensitive to masses and number densities of individual galaxies at early stages while at later stages collective behavior of the particles is more pronounced. This validates our earlier work obtained from different considerations. [ABSTRACT FROM AUTHOR]

We present the spatial clustering properties of 1466 X-ray-selected active galactic nuclei (AGN) compiled from the Chandra Deep Field (CDF) North and South, extended CDF-S, COSMOS and All-wavelength Extended Groth strip International Survey (AEGIS) fields in the 0.5–8 keV band. The X-ray sources span the redshift interval 0 < z < 3 and have a median value of $\bar{z}=0.976$. We employ the projected two-point correlation function to infer the spatial clustering and find a clustering length of r0 = 7.2 ± 0.6 h−1 Mpc and a slope of γ = 1.48 ± 0.12, which corresponds to a bias of $b(\bar{z})=2.26 \pm 0.16$. Using two different halo bias models, we consistently estimate an average dark-matter host halo mass of Mh ≃ 1.3(± 0.3) × 1013 h−1 M⊙. The X-ray AGN bias and the corresponding dark-matter host halo mass are significantly higher than the corresponding values of optically selected AGN (at the same redshifts). The redshift evolution of the X-ray-selected AGN bias indicates, in agreement with other recent studies, that a unique dark-matter halo mass does not fit well the bias at all the different redshifts probed. Furthermore, we investigate if there is a dependence of the clustering strength on X-ray luminosity. To this end we consider only 650 sources around z ∼ 1 and we apply a procedure to disentangle the dependence of clustering on redshift. We find indications for a positive dependence of the clustering length on X-ray luminosity, in the sense that the more luminous sources have a larger clustering length and hence a higher dark-matter halo mass. In detail we find for an average luminosity difference of δ log10Lx ≃ 1 a halo mass difference of a factor of ∼3.These findings appear to be consistent with a galaxy formation model where the gas accreted on to the supermassive black hole in intermediate-luminosity AGN comes mostly from the hot-halo atmosphere around the host galaxy. [ABSTRACT FROM PUBLISHER]

ABSTRACT The distributions of galaxies in the environments of 16 large radio sources have been examined using the Sloan Digital Sky Survey (SDSS). In the giant radio galaxy J1552+2005 (3C 326) which has the highest arm-length ratio, the shorter arm is found to interact with a group of galaxies which forms part of a filamentary structure. Although most large sources occur in regions of low galaxy density, the shorter arm is brighter in most cases suggesting asymmetries in the intergalactic medium which may not be apparent in the distribution of galaxies. In two cases with strong and variable cores, J0313+4120 and J1147+3501, the large flux density asymmetries are possibly also caused by the effects of relativistic motion. [ABSTRACT FROM AUTHOR]

Context. Star-forming galaxies are highly biased tracers of the underlying dark matter density field. Their clustering can be studied through the cosmic infrared background (CIB) anisotropies. These anisotropies have been measured from 100 μm to 2 mm in the past few years. Aims. In this paper, we present a fully parametric model allowing joint analysis of these recent observations. Methods. To develop a coherent model at various wavelengths, we rely on two building blocks. The first one is a parametric model that describes the redshift evolution of the luminosity function of star-forming galaxies. It compares favorably to measured differential number counts and luminosity functions. The second is a halo model-based description of the clustering of galaxies. Starting from a fiducial model, we investigate parameter degeneracies using a Fisher analysis. We then discuss how halos of different masses and redshifts and how LIRGs and ULIRGs contribute to the CIB angular power spectra. Results. From the Fisher analysis, we conclude that we cannot constrain the parameters of the model of evolution of galaxies using clustering data only. The use of combined data of Cl, counts, and luminosity functions improves the constraints slightly but does not remove any degeneracies. In contrast, the measurement of the anisotropies allows us to set interesting constraints on the halo model parameters, even if some strong degeneracies remain. Using our fiducial model, we establish that the 1-halo and 2-halo terms are not sensitive to the same mass regime. We also illustrate how the 1-halo term can be misinterpreted with the Poisson noise term. Conclusions. We present a new model of the clustering of infrared galaxies. Our framework allows a coherent and joint analysis of various probes of infrared galaxies: number counts, luminosity functions, and clustering measurements; however, such a model has a few limitations, such as the parameters of the halo occupation that suffer from strong degeneracies. [ABSTRACT FROM AUTHOR]

We examine cosmic energy equation for extended galaxy structures on the basis of different models of universe. We also extend the power spectrum and density fluctuations for extended structure by introducing softening parameter both for linear and non-linear regimes. The results are compared with earlier results of point mass structures. It is found that softening parameters introduced in the theory influence the thermodynamic fluctuation theory. Results obtained with spectrum analysis are also compared with Riemannian geometric approach (Ruppeiner in Rev. Mod. Phys. 67:605, ) to the galaxy clustering. The singular solutions of thermodynamic fluctuation results can be interpreted on the basis of power spectrum analysis in terms of power index law of two point correlation function. [ABSTRACT FROM AUTHOR]

Neutral hydrogen is ubiquitous, absorbing and emitting 21-cm radiation throughout much of the Universe's history. Active sources of perturbations, such as cosmic strings, would generate simultaneous perturbations in the distribution of neutral hydrogen and in the cosmic microwave background (CMB) radiation from recombination. Moving strings would create wakes leading to 21-cm brightness fluctuations, while also perturbing CMB light via the Gott–Kaiser–Stebbins effect. This would lead to spatial correlations between the 21-cm and CMB anisotropies. Passive sources, like inflationary perturbations, predict no cross-correlations prior to the onset of reionization. Thus, observation of any cross-correlation between CMB and 21-cm radiation from dark ages would constitute evidence for new physics. We calculate the cosmic string-induced correlations between CMB and 21-cm radiation and evaluate their observability. [ABSTRACT FROM AUTHOR]