Voids are promising cosmological probes. Nevertheless, every cosmological test based on voids must necessarily employ methods to identify them in redshift space. Therefore, redshift-space distortions (RSD) and the Alcock-Paczynski effect (AP) have an impact on the void identification process itself generating distortion patterns in observations. Using a spherical void finder, we developed a statistical and theoretical framework to describe physically the connection between the identification in real and redshift space. We found that redshift-space voids above the shot noise level have a unique real-space counterpart spanning the same region of space, they are systematically bigger and their centres are preferentially shifted along the line of sight. The expansion effect is a by-product of RSD induced by tracer dynamics at scales around the void radius, whereas the off-centring effect constitutes a different class of RSD induced at larger scales by the global dynamics of the whole region containing the void. The volume of voids is also altered by the fiducial cosmology assumed to measure distances, this is the AP change of volume. These three systematics have an impact on cosmological statistics. In this work, we focus on the void size function. We developed a theoretical framework to model these effects and tested it with a numerical simulation, recovering the statistical properties of the abundance of voids in real space. This description depends strongly on cosmology. Hence, we lay the foundations for improvements in current models of the abundance of voids in order to obtain unbiased cosmological constraints from redshift surveys.
We investigate the dynamics of a single spherical void embedded in a Friedmann-Lemaître universe, and analyze the void shape in the redshift space. We find that the void in the redshift space appears as an ellipse shape elongated in the direction of the line of sight (i.e., an opposite deformation to the Kaiser effect). Applying this result to observed void candidates at the redshift z~1-2, it may provide us with a new method to evaluate the cosmological parameters, in particular the value of a cosmological constant.
Cosmic voids found in galaxy surveys are defined based on the galaxy distribution in redshift space. We show that the large scale distribution of voids in redshift space traces the fluctuations in the dark matter density field δ(k) (in Fourier space with μbeing the line of sight projected k-vector): δ_v^s(k) = (1 + β_v μ^2) b^s_v δ(k), with a beta factor that will be in general different than the one describing the distribution of galaxies. Only in case voids could be assumed to be quasi-local transformations of the linear (Gaussian) galaxy redshift space field, one gets equal beta factors β_v…
We present new numerical tools to analyse cosmic void catalogues, implemented inside the CosmoBolognaLib, a large set of Open Source C++/Python numerical libraries. The CosmoBolognaLib provides a common numerical environment for cosmological calculations. This work extends these libraries by adding new algorithms for cosmological analyses of cosmic voids, covering the existing gap between theory and observations. We implemented new methods to model the size function of cosmic voids, in both observed and simulated samples of dark matter and biased tracers. Moreover, we provide new numerical too…
We construct an analytic model for the void-galaxy cross-correlation function that enables theoretical predictions of the dipole signal produced dominantly by the gravitational redshift within voids for the first time. By extending a theoretical formulation for the redshift-space distortion of galaxies to include the second order terms of the galaxy peculiar velocity $\bm v$ and the gravitational potential, we formulate the void-galaxy cross-correlation function multipoles in the redshift space, the monopole $ξ_0^{(s)}$, dipole $ξ_1^{(s)}$ and quadrupole $ξ_2^{(s)}$. We find that the dipole $ξ…
We study the ellipticity probability distribution function (PDF) of voids in redshift space with galaxies as tracers of the shapes of voids. We find that the redshift space distortion on the shape of voids statistically increases the ellipticities of voids, and leaves a prominent feature on the ellipticity PDF as a substantial reduction in the probability of having voids with small ellipticity. The location of this characteristic cutoff of the ellipticity PDF is an explicit function of the logarithmic growth rate, and it can be used as a probe of cosmology once the radial density profile of vo…
We have derived estimators for the linear growth rate of density fluctuations using the cross-correlation function of voids and haloes in redshift space, both directly and in Fourier form. In linear theory, this cross-correlation contains only monopole and quadrupole terms. At scales greater than the void radius, linear theory is a good match to voids traced out by haloes in N-body simulations; small-scale random velocities are unimportant at these radii, only tending to cause small and often negligible elongation of the redshift-space cross-correlation function near its origin. By extracting …
We produce the most comprehensive public void catalog to date using the Sloan Digital Sky Survey Data Release 7 main sample out to redshift z=0.2 and the luminous red galaxy sample out to z=0.44. Using a modified version of the parameter-free void finder ZOBOV, we fully take into account the presence of the survey boundary and masks. Our strategy for finding voids is thus appropriate for any survey configuration. We produce two distinct catalogs: a complete catalog including voids near any masks, which would be appropriate for void galaxy surveys, and a bias-free catalog of voids away from any…
Using the redshift-space distortions of void-galaxy cross-correlation function we analyse the dynamics of voids embedded in different environments. We compute the void-galaxy cross-correlation function in the Sloan Digital Sky Survey (SDSS) in terms of distances taken along the line of sight and projected into the sky. We analyse the distortions on the cross-correlation isodensity levels and we find anisotropic isocontours consistent with expansion for large voids with smoothly rising density profiles and collapse for small voids with overdense shells surrounding them. Based on the linear appr…
We present a detailed description of our void finding algorithm which is an extension of the prescription by Hoyle and Vogeley (2002). We include a discussion of the reproducibility and robustness of the algorithm as well as the statistical significance of the detected voids. We apply our void finder to the Data Release 5 (DR5) of the Sloan Digital Sky Survey (SDSS) and identify 232 cosmological voids. A void catalog which contains the most salient properties of the detected voids is created. We present a statistical analysis of the distribution of the size, shape and orientation of our identi…
Spherically symmetric, static model of the cosmological voids is constructed in the framework of the Tolman-Oppenheimer-Volkov equation with the cosmological constant. Extension of the Tooper result (dimensionless form of the TOV equation) is provided for non-zero $Λ$. Then, the equation is simplified in $α\to 0$, $λ\to 0$, $λ/α= const$ regime, suitable for largest structures in $Λ$-dominated universe. Voids are treated as an underdensity regions in the static Einstein universe. Both overdensity and underdensity (relative to static universe) solutions exist. They are identified with standard a…
A simple inhomogeneous cosmological model with a local void is constrained with the latest Union supernova compilation. To fit the supernova data, a large local void on the scales of 1 Gpc is found, contrary to the small scales of 200 Mpc in the previous finding. A more realistic inhomogeneous cosmological model may be required to fit the supernova data. Alternatively, a clumpy universe with clumpiness parameter < 1 can fit the supernova data with reduced local void scales.
We present a new method of finding cosmic voids using tomographic maps of Lyα forest flux. We identify cosmological voids with radii of 2 - 12 $h^{-1}$Mpc in a large N-body simulation at $z = 2.5$, and characterize the signal of the high-redshift voids in density and Lyα forest flux. The void properties are similar to what has been found at lower redshifts, but they are smaller and have steeper radial density profiles. Similarly to what has been found for low-redshift voids, the radial velocity profiles have little scatter and agree very well with the linear theory prediction. We run the same …
The characterisation of cosmic voids gives unique information about the large-scale distribution of galaxies, their evolution and the cosmological model. We identify and characterise cosmic voids in the VIMOS Public Extragalactic Redshift Survey (VIPERS) at redshift 0.55 < z < 0.9. A new void search method is developed based upon the identification of empty spheres that fit between galaxies. The method can be used to characterise the cosmic voids despite the presence of complex survey boundaries and internal gaps. We investigate the impact of systematic observational effects and validate the m…
In this work, we study the cosmological constant problem and Hubble tension in the void-dominated cosmology scenario \cite{Yusofi:2022hgg}. For this goal, we will first consider the cosmic voids in the cosmic web as interconnected ideal spherical bubbles at the early Planck scale and late large scale. By heuristic calculations for each cosmic void, we obtain particular mass density and cosmological constant that are the same order of magnitude as the entire universe on any scale. The values obtained for the cosmological constant vary from scale to scale. As a result, it will be shown that ther…
Redshift space distortions (RSD) in the void-galaxy correlation $ξ^s$ provide information on the linear growth rate of structure in low density environments. Accurate modelling of these RSD effects can also allow the use of voids in competitive Alcock-Paczynski measurements. Linear theory models of $ξ^s$ are able to provide extremely good descriptions of simulation data on all scales provided the real space void positions are known. However, by reference to simulation data we demonstrate the failure of the assumptions implicit in current models of $ξ^s$ for voids identified directly in redshif…
This is the second part of a thorough investigation of the redshift-space effects that affect void properties and the impact they have on cosmological tests. Here, we focus on the void-galaxy cross-correlation function, specifically, on the projected versions that we developed in a previous work. The pillar of the analysis is the one-to-one relationship between real and redshift-space voids above the shot-noise level identified with a spherical void finder. Under this mapping, void properties are affected by three effects: (i) a systematic expansion as a consequence of the distortions induced …
We study the redshift drift, i.e., the time derivative of the cosmological redshift in the Lemaître-Tolman-Bondi (LTB) solution in which the observer is assumed to be located at the symmetry center. This solution has often been studied as an anti-Copernican universe model to explain the acceleration of cosmic volume expansion without introducing the concept of dark energy. One of decisive differences between LTB universe models and Copernican universe models with dark energy is believed to be the redshift drift. The redshift drift is negative in all known LTB universe models, whereas it is pos…
We study evolution of voids in cosmological simulations using a new method for tracing voids over cosmic time. The method is based on tracking watershed basins (contiguous regions around density minima) of well developed voids at low redshift, on a regular grid of density field. It enables us to construct a robust and continuous mapping between voids at different redshifts, from initial conditions to the present time. We discuss how the new approach eliminates strong spurious effects of numerical origin when voids evolution is traced by matching voids between successive snapshots (by analogy t…
We compare the evolution of voids formed under the standard cosmological model and two alternative cosmological models. The two models are a quintessence model ($ϕ$CDM) and a Coupled Dark Matter-Dark Energy (CDE) model, both of which have evolving and interacting dark sectors. From $N$-body adiabatic hydrodynamical simulations of these models, we measure the statistics and quantify the properties of voids over the redshift range $z=1.5-12$: these include their population size, volumes, shapes and average densities. We find that the latter property has potential as a probe of cosmology, particu…
We report on the first application of the Alcock-Paczynski test to stacked voids in spectroscopic galaxy redshift surveys.We use voids from the Sutter et al. (2012) void catalog, which was derived from the Sloan Digital Sky Survey Data Release 7 main sample and luminous red galaxy catalogs. The construction of that void catalog removes potential shape measurement bias by using a modified version of the ZOBOV algorithm and by removing voids near survey boundaries and masks. We apply the shape-fitting procedure presented in Lavaux & Wandelt (2012) to ten void stacks out to redshift z=0.36. Combi…
Modifications to General Relativity (GR) often incorporate screening mechanisms in order to remain compatible with existing tests of gravity. The screening is less efficient in underdense regions, which suggests that cosmic voids can be a useful cosmological probe for constraining modified gravity models. In particular, weak lensing by voids has been proposed as a promising test of such theories. Usually, voids are identified from galaxy distributions, making them biased tracers of the underlying matter field. An alternative approach is to study voids identified in weak lensing maps -- weak le…
We present a comparison of void properties between the standard model of cosmology, $Λ$ Cold Dark Matter ($Λ$CDM), and two alternative cosmological models with evolving and interacting dark sectors: a quintessence model ($ϕ$CDM) and a Coupled Dark Matter-Dark Energy (CDE) model. Using $N$-body simulations of these models, we derive several measures of void statistics and properties, including distributions of void volume, ellipticity, prolateness, and average density. We find that the volume distribution derived from the CDE simulation deviates from the volume distribution derived from the $Λ$…
Cosmic voids constitute promising cosmological laboratories. However, a full description of all the redshift-space effects that affect observational measurements is mandatory in order to obtain unbiased cosmological constraints. We make a description in a nutshell of these effects and lay the theoretical foundations for designing reliable cosmological tests based on the void size function and the void-galaxy cross-correlation function. We show that modern spectroscopic surveys offer a high signal-to-noise ratio to detect and study them.
Redshift space distortions within voids provide a unique method to test for environmental dependence of the growth rate of structures in low density regions, where effects of modified gravity theories might be important. We derive a linear theory model for the redshift space void-galaxy correlation that is valid at all pair separations, including deep within the void, and use this to obtain expressions for the monopole $ξ^s_0$ and quadrupole $ξ^s_2$ contributions. Our derivation highlights terms that have previously been neglected but are important within the void interior. As a result our mod…
Exploring Cosmological Constraints of the Void-Lensing Cross-Correlation in the CSST Photometric Survey
National Astronomical Observatories, Chinese Academy of Sciences（中国科学院国家天文台）；School of Astronomy and Space Sciences, University of Chinese Academy of Sciences(UCAS)（中国科学院大学天文与空间科学学院）；Science Center for China Space Station Telescope, National Astronomical Observatories, Chinese Academy of Science（中国科学院国家天文台中国空间站望远镜科学中心）
We investigate the potential of using cosmic voids as a probe to constrain cosmological parameters through the gravitational lensing effect of the cosmic microwave background (CMB) and make predictions for the next generation surveys. By assuming the detection of a series of $\approx 5 - 10$ voids along a line of sight within a square-degree patch of the sky, we found that they can be used to break the degeneracy direction of some of the cosmological parameter constraints (for example $ω_b$ and $Ω_Λ$) in comparison with the constraints from random CMB skies with the same size area for a survey…
We present catalogues of voids for the SDSS DR7 redshift survey and for Millennium I simulation mock data. We aim to compare the observations with simulations based on a $Λ$CDM model and a semi-analytic galaxy formation model. We use the void statistics as a test for these models. We assembled a mock catalogue that closely resembles the SDSS DR7 catalogue and carried out a parallel statistical analysis of the observed and simulated catalogue. We find that in the observation and the simulation, voids tend to be equally spherical. The total volume occupied by the voids and their total number are…
Cosmic voids are promising cosmological laboratories for studying the dark energy phenomenon and alternative gravity theories. They are receiving special attention nowadays in view of the new generation of galaxy spectroscopic surveys, which are covering an unprecedented volume and redshift range. There are two primary statistics in void studies: (i) the void size function, which characterises the abundance of voids, and (ii) the void-galaxy cross-correlation function, which contains information about the density and velocity fields in these regions. However, it is necessary a complete descrip…
DESIVAST: A Catalog of Low-Redshift Voids using Data from the DESI DR1 Bright Galaxy Survey
University of Rochester（罗切斯特大学）；Lawrence Berkeley National Laboratory（劳伦斯伯克利国家实验室）；Boston University（波士顿大学）；Università degli Studi di Milano（米兰大学）；University College London（伦敦大学学院）；Durham University（杜伦大学）
We use properties of void populations identified in $N$-body simulations to forecast the ability of upcoming galaxy surveys to differentiate models of f(R) gravity from \lcdm~cosmology. We analyze multiple simulation realizations, which were designed to mimic the expected number densities, volumes, and redshifts of the upcoming Euclid satellite and a lower-redshift ground-based counterpart survey, using the public {\tt VIDE} toolkit. We examine void abundances, ellipicities, radial density profiles, and radial velocity profiles at redshifts 1.0 and 0.43. We find that stronger f(R) coupling str…
Using survey data and numerical LCDM modeling we establish an optimized fit to the generalized Reduced Void Probability Function, RVPF, of Mikjian used to establish a statistical foundation to any physical process associated with hierarchical clustering. We use a numerical N-body cosmological simulation code, GADGET-2, to investigate the sensitivity of the distribution of voids characterized by the RVPF to a general hierarchical reduced void parameter, a. The void parameter is related to the Levy stability index of the distribution and Fischer critical exponent used in clustering models. We nu…
The stability of voids in the Local Universe: The role of the cosmological constant
Center for Cosmology and Astrophysics, Alikhanian National Laboratory（宇宙学与天体物理学中心，阿利哈尼扬国家实验室）；Yerevan State University（埃里温国立大学）；SIA, Sapienza University of Rome（罗马智慧大学）；Keldysh Institute of Applied Mathematics of RAS（俄罗斯科学院凯尔迪什应用数学研究所）
Cosmic voids are large underdense regions that, together with galaxy clusters, filaments and walls, build up the large-scale structure of the Universe. The void size function provides a powerful probe to test the cosmological framework. However, to fully exploit this statistics, the void sample has to be properly cleaned from spurious objects. Furthermore, the bias of the mass tracers used to detect these regions has to be taken into account in the size function model. In our work we test a cleaning algorithm and a new void size function model on a set of simulated dark matter halo catalogues,…
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 $\rmΛ$ cold dark matter Universe with state-of-the-art subgrid models for baryonic processes in a $(…
The paper studies the correction to the distance modulus induced by inhomogeneities and averaged over all directions from a given observer. The inhomogeneities are modeled as mass-compensated voids in random or regular lattices within Swiss-cheese universes. Void radii below 300 Mpc are considered, which are supported by current redshift surveys and limited by the recently observed imprint such voids leave on CMB. The averaging over all directions, performed by numerical ray tracing, is non-perturbative and includes the supernovas inside the voids. Voids aligning along a certain direction prod…
The Lyman-alpha forest is a unique probe of large-scale matter density fluctuations at high redshift (z > 2). It is possible to obtain 3D maps of the matter distribution from Lyman-alpha data, using tomographic reconstruction methods. Here, we present the largest tomographic map of matter fluctuations at z > 2, over the Gpc^3 volume covered by Lyman-alpha forest from SDSS-IV quasar spectra in the Stripe 82 field. We present a catalog of high-redshift voids constructed from this map. The measurement of the cross-correlation between these voids and the Lyman-alpha forest provides the first obser…
We present a framework for the hierarchical identification and characterization of voids based on the Watershed Void Finder. The Hierarchical Void Finder is based on a generalization of the scale space of a density field invoked in order to trace the hierarchical nature and structure of cosmological voids. At each level of the hierarchy, the watershed transform is used to identify the voids at that particular scale. By identifying the overlapping regions between watershed basins in adjacent levels, the hierarchical void tree is constructed. Applications on a hierarchical Voronoi model and on a…
Two recently proposed techniques, involving the measurement of the cosmic parallax and redshift drift, provide novel ways of directing probing (over a time-span of several years) the background metric of the universe and therefore shed light on the dark energy conundrum. The former makes use of upcoming high-precision astrometry measurements to either observe or put tight constraints on cosmological anisotropy for off-center observers, while the latter employs high-precision spectroscopy to give an independent test of the present acceleration of the universe. In this paper, we show that both m…
Cosmic voids are becoming key players in testing the physics of our Universe. Here we concentrate on the abundances and the dynamics of voids as these are among the best candidates to provide information on cosmological parameters. Cai, Padilla \& Li (2014) use the abundance of voids to tell apart Hu \& Sawicki $f(R)$ models from General Relativity. An interesting result is that even though, as expected, voids in the dark matter field are emptier in $f(R)$ gravity due to the fifth force expelling away from the void centres, this result is reversed when haloes are used to find voids. The abunda…
We present measurements of the anisotropic cross-correlation of galaxies and cosmic voids in data from the Sloan Digital Sky Survey Main Galaxy Sample (MGS), Baryon Oscillation Spectroscopic Survey (BOSS) and extended BOSS (eBOSS) luminous red galaxy catalogues from SDSS Data Releases 7, 12 and 16, covering the redshift range $0.07<z<1.0$. As in our previous work analysing voids in subsets of these data, we use a reconstruction method applied to the galaxy data before void-finding in order to remove selection biases when constructing the void samples. We report results of a joint fit to the mu…
Extracting the Alcock-Paczynski signal from voids: A novel approach via reconstruction
Aix-Marseille Université（艾克斯-马赛大学）；CNRS/IN2P3, CPPM（法国国家科学研究中心/法国国家粒子物理研究所，CPPM）；Dipartimento di Fisica, Università di Roma Tre（罗马第三大学物理系）；SISSA, International School for Advanced Studies（国际高等研究院）；ICSC - Centro Nazionale di Ricerca in High Performance Computing, Big Data e Quantum Computing（高性能计算、大数据和量子计算国家研究中心）；INFN, Sezione di Trieste（意大利国家核物理研究所的里雅斯特分部）；Université Clermont Auvergne（克莱蒙奥弗涅大学）；CNRS/IN2P3, LPCA（法国国家科学研究中心/法国国家粒子物理研究所，LPCA）；Department of Physics, Università di Genova（热那亚大学物理系）；Istituto Nazionale di Fisica Nucleare, Sezione di Genova（意大利国家核物理研究所热那亚分部）；INAF-Osservatorio Astronomico di Brera（意大利国家天体物理研究所布雷拉天文台）；Department of Astrophysical Sciences, Peyton Hall, Princeton University（普林斯顿大学天体物理科学系）；Université Claude Bernard Lyon 1（里昂第一大学）；IUF, IP2I Lyon（法国高等教育与研究学院，里昂粒子物理与宇宙学研究所）
We study the orientation and density profiles of the cosmological voids with SDSS10 data. Using voids to test Alcock-Paczynski effect has been proposed and tested in both simulations and actual SDSS data. Previous observations imply that there exist an empirical stretching factor which plays an important role in the voids' orientation. Simulations indicate that this empirical stretching factor is caused by the void galaxies' peculiar velocities. Recently Hamaus et al. found that voids' density profiles are universal and their average velocities satisfy linear theory very well. In this article …
Cosmic voids are an important probe of large-scale structure that can constrain cosmological parameters and test cosmological models. We present a new paradigm for void studies: void detection in weak lensing convergence maps. This approach identifies objects that relate directly to our theoretical understanding of voids as underdensities in the total matter field and presents several advantages compared to the customary method of finding voids in the galaxy distribution. We exemplify this approach by identifying voids using the weak lensing peaks as tracers of the large-scale structure. We fi…
The bias of dark matter halos and galaxies is a crucial quantity in many cosmological analyses. In this work, using large cosmological simulations, we explore the halo mass function and halo bias within cosmic voids. For the first time to date, we show that they are scale-dependent along the void profile, and provide a predictive theoretical model of both the halo mass function and halo bias inside voids, recovering for the latter and 1% accuracy against simulated data. These findings may help shed light on the dynamics of halo formation within voids and improve the analysis of several void st…
We identified voids in the completed VIMOS Public Extragalactic Redshift Survey (VIPERS), using an algorithm based on searching for empty spheres. We measured the cross-correlation between the centres of voids and the complete galaxy catalogue. The cross-correlation function exhibits a clear anisotropy in both VIPERS fields (W1 and W4), which is characteristic of linear redshift space distortions. By measuring the projected cross-correlation and then deprojecting it we are able to estimate the undistorted cross-correlation function. We propose that given a sufficiently well measured cross-corr…
Using cosmic voids to probe the growth rate of cosmic structure, and hence the nature of dark energy, is particularly interesting in the context of modified gravity theories that rely on the screening mechanism. In this work we improve the modelling of redshift-space distortions around voids in the dark matter density field, and thus reduce systematic errors in the derivation of cosmological parameters. We also show how specific types of voids can be used to better probe the growth rate, using a flexible void finder. We apply our results to test for a quintessence type of dark energy vs. a LCD…
Max Planck Institute for Extraterrestrial Physics（马克斯·普朗克地外物理研究所）；Center for Computational Astrophysics, Flatiron Institute（平顿研究所计算天体物理学中心）；ICTP, International Centre for Theoretical Physics（国际理论物理中心）
We have carried out a redshift survey using the VIMOS spectrograph on the VLT towards the Cosmic Microwave Background cold spot. A possible cause of the cold spot is the Integrated Sachs-Wolfe effect imprinted by an extremely large void (hundreds of Mpc in linear dimension) at intermediate or low redshifts. The redshift distribution of over seven hundred z<1 emission-line galaxies drawn from an I-band flux limited sample of galaxies in the direction of the cold spot shows no evidence of a gap on scales of Delta-z> 0.05 as would be expected if such a void existed at 0.35<z<1. There are troughs …
J-PAS & FLAMINGO: Cosmic voids and void galaxies in the gravitational landscape of photometric surveys
University of Tartu（塔尔图大学）；University of Groningen（格罗宁根大学）；University of Turku（图尔库大学）；Leiden University（莱顿大学）；Universidade de São Paulo（圣保罗大学）；Instituto de Astronomia, Geofísica e Ciências Atmosféricas da USP（圣保罗大学天文、地球物理与大气科学研究所）；Centro de Estudios de Física del Cosmos de Aragón (CEFCA)（阿拉贡宇宙物理研究中心）
