Cosmic Voids Research Articles

Cosmic voids and induced hyperbolicity. II. Sensitivity to void/wall scales

Cosmic voids as typical under-density regions in the large-scale Universe are known for their hyperbolic properties as an ability to deviate the photon beams. The under-density then is acting as the negative curvature in the hyperbolic spaces. The hyperbolicity of voids has to lead to distortion in the statistical analysis at galactic surveys. We reveal the sensitivity of the hyperbolicity and hence of the distortion with respect to the ratio of void/wall scales which are observable parameters. This provides a principal possibility to use the distortion in the galactic surveys in revealing the line-of-sight number of cosmic voids and their characteristic scales.

The persistence of large scale structures. Part I. Primordial non-Gaussianity

We develop an analysis pipeline for characterizing the topology of large scale structure and extracting cosmological constraints based on persistent homology. Persistent homology is a technique from topological data analysis that quantifies the multiscale topology of a data set, in our context unifying the contributions of clusters, filament loops, and cosmic voids to cosmological constraints. We describe how this method captures the imprint of primordial local non-Gaussianity on the late-time distribution of dark matter halos, using a set of N-body simulations as a proxy for real data analysis. For our best single statistic, running the pipeline on several cubic volumes of size 40 (Gpc/h)3, we detect fNL loc=10 at 97.5% confidence on ∼ 85% of the volumes. Additionally wetest our ability to resolve degeneracies betweenthe topological signature of fNL loc and variation of σ8 and argue that correctly identifying nonzero fNL loc in this case is possible via an optimal template method. Our method relies on information living at \U0001d4aa(10) Mpc/h, a complementary scale with respect to commonly used methods such as the scale-dependent bias in the halo/galaxy power spectrum. Therefore, while still requiring a large volume, our method does not require sampling long-wavelength modes to constrain primordial non-Gaussianity. Moreover, our statistics are interpretable: we are able to reproduce previous results in certain limits and we make new predictions for unexplored observables, such as filament loops formed by dark matter halos in a simulation box.

Identification of Cosmic Voids as Massive Cluster Counterparts

Abstract We develop a method to identify cosmic voids from the matter density field by adopting a physically motivated concept that voids are the counterpart of massive clusters. To prove the concept we use a pair of ΛCDM simulations, a reference and its initial density-inverted mirror simulation, and study the relation between the effective size of voids and the mass of corresponding clusters. Galaxy cluster-scale dark matter halos are identified in the Mirror simulation at z = 0 by linking dark matter particles. The void corresponding to each cluster is defined in the Reference simulation as the region occupied by the member particles of the cluster. We study the voids corresponding to the halos more massive than 1013 h −1 M ⊙. We find a power-law scaling relation between the void size and the corresponding cluster mass. Voids with a corresponding cluster mass above 1015 h −1 M ⊙ occupy ∼1% of the total simulated volume, whereas this fraction increases to ∼54% for voids with a corresponding cluster mass above 1013 h −1 M ⊙. It is also found that the density profile of the identified voids follows a universal functional form. Based on these findings, we propose a method to identify cluster-counterpart voids directly from the matter density field without their mirror information by utilizing three parameters such as the smoothing scale, density threshold, and minimum core fraction. We recover voids corresponding to clusters more massive than 3 × 1014 h −1 M ⊙ at a 70%–74% level of completeness and reliability. Our results suggest that we are able to identify voids in a way to associate them with clusters of a particular mass scale.

The Nonvelocity Cosmological Spectral Shift

Beginning from the premise that the universe is static, and that the cosmological redshift is due to a nonconservative tired light effect, the following examines evidence supporting the prediction that photons will progressively blueshift when transiting through the gravity wells of galaxies, galaxy clusters, and superclusters. The presence of such a nonvelocity blueshift effect is seen to make a substantial contribution to Virgo cluster galaxy spectra, sufficient to dramatically decrease the cluster’s velocity dispersion and assessed virial mass and eliminate the need to assume the presence of large quantities of dark matter. The effect is also shown to account for the Fingers-of-God effect and Kaiser pancaking effect seen when the spectra of cluster galaxies are plotted in redshift space. The opposite effect, excessive redshifting of photons passing through cosmic voids is able to explain void elongation in redshift space, and also the subnormal luminosity of void galaxies. The proposed cosmological blueshifting phenomenon also explains the downturn of the slope of the Hubble Flow in the vicinity of the Local Group which projects a negative apparent velocity for photons propagating near the Milky Way. It also offers an explanation for the blueshift of the Andromeda galaxy spectra and for Arp’s findings that the spectra of primary galaxies in a cluster tend to be blueshifted relative to their companion galaxies. These photon energy phenomena are anticipated by the physics of subquantum kinetics which predicts that photons traversing long distances through intergalactic space should undergo nonconservative tired-light redshifting, and that photons passing through gravity potential wells should undergo progressive blueshifting. The latter effect may be visualized as a negative nonvelocity Hubble constant.

A Conceptual Model to Explain Dark Matter and Dark Energy

This paper considers a conceptual model that attempts to explain ‘Dark Matter’ and ‘Dark Energy’. The model is based on considering a gravitational field to be the result of a mass (a Higgs field) scattering pre-existing cosmic background space-time waves or ‘Uber-waves’. The term ‘Uber’ is used to denote an outstanding or supreme example of a particular kind of gravitational wave with cosmic-scale wavelengths that are far in excess of those associated with the gravitational waves generated by accelerating masses. Such waves are taken to be the very lowest frequency components associated with the spectrum of space-time waves generated by the ‘Big Bang’ and are supported by the expanding fabric of space-time produced at the point of the big bang, i.e. the lowest frequency components of a cosmological spectrum whose bandwidth is the a Planck frequency (～10∧43 Hz). Like electromagnetic waves, Uber waves are taken to propagate with an upper velocity consistent with the speed of light and interact with, and are scattered by, a Higgs field. This interaction produces the effect of a mass locally curving space-time, an idea that is contrary to the conventional model associated with General Relativity where mass is taken to curve space-time directly which otherwise remains ‘flat’. By assuming the pre-existence of background Uber waves, we consider the concave curvature of such waves to generate an apparent attractive gravitational force. This interaction produces the effect of a mass locally curving space-time, an idea that is contrary to the conventional model associated with General Relativity where mass is taken to curve space-time directly which otherwise remains ‘flat’. By assuming the pre-existence of background Uber waves, we consider the concave curvature of such waves to generate an apparent attractive gravitational force. This attractive force is taken to govern the formation of large scale structures of matter (galaxies and super-clusters of galaxies, for example) in the conventional sense but surrounded by a residual background gravitational field. It is this residual field that gives rise to the effect known as dark matter where more gravity (as an attractive only force) appears to be available than that which can be accounted for by the observed (luminous) mass, a luminosity that is generated primarily by nuclear fusion in stars. The convex curvature of Uber waves is considered to account for cosmic voids within which gravity is a repulsive force and where large scale structures of matter can therefore not be formed. This is considered to explain the super-large cosmic voids or super voids that are observed. These are regions of the universe where there is an absence of rich super clusters of matter. In these anti-gravity zones, only relatively small structures of matter can be formed by electrostatic forces alone which are then repelled from each other when their mass becomes significant enough for the force of anti-gravity to become significant. In such regions of an Uber wave, the matter generated from electrostatic forces builds up to produce a weak gravitational repulsive field due to the low mass density within a void. However, due to the immense size of these cosmic voids, they are taken to generate a net repulsive force which is considered to be the reason for the acceleration associated with the expansion of the universe; the effect of dark energy. This effect also accounts for the cosmic web structure in which luminescent matter appears to exist in relatively thin connective filaments. The purpose of this paper is to provide a conceptual model and not to investigate the ideas proposed in any significant mathematical detail. This is accomplished by building up the ideas on a case-by-case basis, coupled with a series of thought experiments but without resorting to specific physical scales or the physical parameters associated with these scales other than, by default, the speed of light and Newton’s gravitational constant.

Constraining reionization in progress at z = 5.7 with Lyman-α emitters: voids, peaks, and cosmic variance

ABSTRACT A number of independent observations suggest that the intergalactic medium was significantly neutral at z = 7 and that reionization was, perhaps, still in progress at z = 5.7. The narrowband survey, SILVERRUSH, has mapped over 2000 Lyman-α emitters (LAEs) at these redshifts ( G58). Previous analyses have assumed that reionization was over by z = 5.7, but this data may actually sample the final stages of reionization when the last neutral islands were relegated to the cosmic voids. Motivated by these developments, we re-examine LAE void and peak statistics and their ability to constrain reionization. We construct models of the LAE distribution in (1 Gpc h−1)3 volumes, spanning a range of neutral fractions at z = 5.7 and 6.6. Models with a higher neutral fraction show an enhanced probability of finding holes in the LAE distribution. When comparing models at fixed mean surface density, however, LAEs obscured by neutral gas in the voids must be compensated by visible LAEs elsewhere. Hence, in these models, the likelihood of finding an overdense peak is also enhanced in the latter half of reionization. Compared to the widely used angular two-point correlation function (2PCF), we find that the void probability function (VPF) provides a more sensitive test of models during the latter half of reionization. By comparison, at neutral fractions $\sim 50{{\ \rm per\ cent}}$, the VPF and a simple peak thresholding statistic are both similar to the 2PCF in constraining power. Lastly, we find that the cosmic variance and large-scale asymmetries observed in the SILVERRUSH fields are consistent with large-scale structure in a ΛCDM universe.

Cosmic voids and induced hyperbolicity

Cosmic voids - the low density regions in the Universe - as characteristic features of the large scale matter distribution, are known for their hyperbolic properties. The latter implies the deviation of photon beams due to their underdensity, thus mimicing the negative curvature. We now show that the hyperbolicity can be induced not only by negative curvature or underdensity but also depends on the anisotropy of the photon beams.

Precision cosmology with voids in the final BOSS data

We report novel cosmological constraints obtained from cosmic voids in the final BOSS DR12 dataset. They arise from the joint analysis of geometric and dynamic distortions of average void shapes (i.e., the stacked void-galaxy cross-correlation function) in redshift space. Our model uses tomographic deprojection to infer real-space void profiles and self-consistently accounts for the Alcock-Paczynski (AP) effect and redshift-space distortions (RSD) without any prior assumptions on cosmology or structure formation. It is derived from first physical principles and provides an extremely good description of the data at linear perturbation order. We validate this model with the help of mock catalogs and apply it to the final BOSS data to constrain the RSD and AP parameters f/b and DA H/c, where f is the linear growth rate, b the linear galaxy bias, DA the comoving angular diameter distance, H the Hubble rate, and c the speed of light. In addition, we include two nuisance parameters in our analysis to marginalize over potential systematics. We obtain f/b=0.540±0.091 and DA H/c=0.588±0.004 from the full void sample at a mean redshift of z=0.51. In a flat ΛCDM cosmology, this implies Ωm=0.312±0.020 for the present-day matter density parameter. When we use additional information from the survey mocks to calibrate our model, these constraints improve to f/b=0.347±0.023, DA H/c=0.588±0.003, and Ωm = 0.310 ± 0.017. However, we emphasize that the calibration depends on the specific model of cosmology and structure formation assumed in the mocks, so the calibrated results should be considered less robust. Nevertheless, our calibration-independent constraints are among the tightest of their kind to date, demonstrating the immense potential of using cosmic voids for cosmology in current and future data.

How to build a catalogue of linearly evolving cosmic voids

ABSTRACT Cosmic voids provide a powerful probe of the origin and evolution of structures in the Universe because their dynamics can remain near-linear to the present day. As a result, they have the potential to connect large-scale structure at late times to early Universe physics. Existing ‘watershed’-based algorithms, however, define voids in terms of their morphological properties at low redshift. The degree to which the resulting regions exhibit linear dynamics is consequently uncertain, and there is no direct connection to their evolution from the initial density field. A recent void definition addresses these issues by considering ‘anti-haloes’. This approach consists of inverting the initial conditions of an N-body simulation to swap overdensities and underdensities. After evolving the pair of initial conditions, anti-haloes are defined by the particles within the inverted simulation that are inside haloes in the original (uninverted) simulation. In this work, we quantify the degree of non-linearity of both anti-haloes and watershed voids using the Zel’dovich approximation. We find that non-linearities are introduced by voids with radii less than $5\, \mathrm{Mpc}\, h^{-1}$, and that both anti-haloes and watershed voids can be made into highly linear sets by removing these voids.

Void halo mass function: A promising probe of neutrino mass

Cosmic voids, the underdense regions in the universe, are particularly sensitive to diffuse density components such as cosmic neutrinos. This sensitivity is enhanced by the match between void sizes and the free-streaming scale of massive neutrinos. Using the massive neutrino simulations massivenus, we investigate the effect of neutrino mass on dark matter halos as a function of environment. We find that the halo mass function depends strongly on neutrino mass and that this dependence is more pronounced in voids than in high-density environments. An observational program that measured the characteristic mass of the most massive halos in voids should be able to place novel constraints on the sum of the masses of neutrinos $\ensuremath{\sum}{m}_{\ensuremath{\nu}}$. The neutrino mass effect in the simulations is quite strong: In a ${512}^{3}\text{ }\text{ }{h}^{\ensuremath{-}3}\text{ }{\mathrm{Mpc}}^{3}$ survey, the mean mass of the 1000 most massive halos in the void interiors is $(4.82\ifmmode\pm\else\textpm\fi{}0.11)\ifmmode\times\else\texttimes\fi{}{10}^{12}\text{ }\text{ }{h}^{\ensuremath{-}1}\text{ }{M}_{\ensuremath{\bigodot}}$ for $\ensuremath{\sum}{m}_{\ensuremath{\nu}}=0.6\text{ }\text{ }\mathrm{eV}$ and $(8.21\ifmmode\pm\else\textpm\fi{}0.13)\ifmmode\times\else\texttimes\fi{}{10}^{12}\text{ }\text{ }{h}^{\ensuremath{-}1}\text{ }{M}_{\ensuremath{\bigodot}}$ for $\ensuremath{\sum}{m}_{\ensuremath{\nu}}=0.1\text{ }\text{ }\mathrm{eV}$. Subaru (SuMIRe), Euclid and WFIRST will have both spectroscopic and weak lensing surveys. Covering volumes at least 50 times larger than our simulations, they should be sensitive probes of neutrino mass through void substructure.

Dark Energy Survey Year 1 results: the lensing imprint of cosmic voids on the cosmic microwave background

ABSTRACT Cosmic voids gravitationally lens the cosmic microwave background (CMB) radiation, resulting in a distinct imprint on degree scales. We use the simulated CMB lensing convergence map from the Marenostrum Institut de Ciencias de l’Espai (MICE) N-body simulation to calibrate our detection strategy for a given void definition and galaxy tracer density. We then identify cosmic voids in Dark Energy Survey (DES) Year 1 data and stack the Planck 2015 lensing convergence map on their locations, probing the consistency of simulated and observed void lensing signals. When fixing the shape of the stacked convergence profile to that calibrated from simulations, we find imprints at the 3σ significance level for various analysis choices. The best measurement strategies based on the MICE calibration process yield S/N ≈ 4 for DES Y1, and the best-fitting amplitude recovered from the data is consistent with expectations from MICE (A ≈ 1). Given these results as well as the agreement between them and N-body simulations, we conclude that the previously reported excess integrated Sachs–Wolfe (ISW) signal associated with cosmic voids in DES Y1 has no counterpart in the Planck CMB lensing map.

Belousov-Zhabotinsky Reaction, Space Voids and Galaxy Clusters

It is shown that the cause of cosmic voids and galaxy clusters is the chaotic motion of galaxies. According to I. Prigogine, in an open system, near a stationary state, far from equilibrium, fluctuations of parameters are possible. Therefore, in chemical cyclic systems such as the Belousov-Zhabotinsky reaction, the concentration of substances can take on any values, and these values ​​can fluctuate over time. If we assume that the Universe is an open system, which is located near a stationary state (far from equilibrium), then in some regions of the Universe the concentration of galaxies can be any, which inevitably leads to the appearance of clusters of galaxies and space voids.

The Halo Void (Dust) Model of large scale structure

Within the Halo Model of large scale structure, all matter is contained in dark matter halos. This simple yet powerful framework has been broadly applied to multiple data sets and enriched our comprehension of how matter is distributed in the Universe. In this work we extend this assumption by allowing for matter to rest not only inside halos but also within cosmic voids and in between halos and voids (which we call `dust'). This assumption leads to additional contributions (1Void, 2Void, Halo-Void, etc.) to the predictions of correlation functions, spectra and profiles for both halos and voids. Whereas the Halo Model can only make predictions for halo quantities, the Halo Void Model extends those for void statistics and halo-void cross-correlations. We provide recipes for all new ingredients of the Halo Void (Dust) Model, such as the void abundance, linear bias and density profile and test their validity in a N-body simulation. Including voids and dust into the calculations improves the transition between the 1Halo and the 2Halo terms by up to ∼ 6%. It also eliminates the need to include low-mass structures on the normalization of large-scale terms, suggesting that halos and voids are complementary cosmic structures to effectively describe matter distribution on large scales of the Universe.

Dark Matter–Dark Energy Interaction and the Shape of Cosmic Voids

Abstract Interaction between dark matter (DM) and dark energy (DE) is one of the not completely solved problems in cosmology that has been studied extensively. This interaction affects cosmic structures. In this regard, the shape of cosmic voids can be influenced by the DM and DE interaction. Here, employing the dynamical DE model constrained by observational data, we study the effects of this interaction on the ellipticity of cosmic voids. With this aim, we apply the linear growth of density perturbation in the presence of interaction. The probability-density distribution for the ellipticity of cosmic voids is investigated. The results confirm that the ellipticity of cosmic voids increases when the DM and DE interaction is considered.

Posidonius' Cosmology

Posidonius incorporated important concepts of Peripatetic physics into his system. Posidonius adopted a finitist cosmological model where the extra- cosmic void was not infinite but just as large as the cosmos’ size at the time of the conflagration (F 84/97a E ̶ K). He accepted the idea that there are ab- solute directions towards which the elements naturally tend to move and in which they will naturally remain (F 93 E ̶ K). Similarly, Posidonius concei- ved the four elements as interactive given the new relationship of mutual contrariety, and adopted a physicalist approach where the hot elements are active (F 93, F 101 E ̶ K). The analysis of the long fragments preserved in Strabo (F 229 E ̶ K) and Priscianus Lydus (F 219 E ̶ K) has further shown the significance of heat as an active power in Posidonius’ physics.

The Quijote Simulations

The Quijote simulations are a set of 44,100 full N-body simulations spanning more than 7,000 cosmological models in the $\{\Omega_{\rm m}, \Omega_{\rm b}, h, n_s, \sigma_8, M_\nu, w \}$ hyperplane. At a single redshift the simulations contain more than 8.5 trillions of particles over a combined volume of 44,100 $(h^{-1}{\rm Gpc})^3$; each simulation follow the evolution of $256^3$, $512^3$ or $1024^3$ particles in a box of $1~h^{-1}{\rm Gpc}$ length. Billions of dark matter halos and cosmic voids have been identified in the simulations, whose runs required more than 35 million core hours. The Quijote simulations have been designed for two main purposes: 1) to quantify the information content on cosmological observables, and 2) to provide enough data to train machine learning algorithms. In this paper we describe the simulations and show a few of their applications. We also release the Petabyte of data generated, comprising hundreds of thousands of simulation snapshots at multiple redshifts, halo and void catalogs, together with millions of summary statistics such as power spectra, bispectra, correlation functions, marked power spectra, and estimated probability density functions.

How galaxies populate haloes in very low-density environments

Context. Evidence shows that properties of dark matter haloes may vary with large-scale environment. Studying the halo occupation distribution in cosmic voids makes it possible to obtain useful information that can shed light on the subject. The history of the formation of the haloes and galaxies residing in these regions is likely to differ from the global behaviour given their extreme environment. Aims. Our goal is to characterise the halo occupation distribution in the interior of cosmic voids and compare with the general results to unveil the way galaxies populate haloes in simulated galaxy catalogues. Methods. We used two publicly accessible simulated galaxy catalogues constructed with different methods: a semi-analytical model and a hydrodynamic simulation. In both cases, we identified cosmic voids, and we measured the halo occupation distribution inside these regions for different absolute magnitude thresholds. We compared these determinations with the overall results, and we studied the dependence of different characteristics of the voids. We also analysed the stellar content and the formation time of the haloes inside voids and confronted the general halo population results. Results. Inside the voids, we find a significantly different halo occupation distribution with respect to the general results. This is present in all absolute magnitude ranges explored. We obtain no signs of variation related to void characteristics, indicating that the effects depend only on the density of the large-scale environment. Additionally, we find that the stellar-mass content also differs within voids that host haloes with less massive central galaxies (∼10%), as well as satellites with significantly lower stellar-mass content (∼30%). Finally, we find a slight difference between the formation times of the younger haloes in voids than the average population. These characteristics indicate that haloes populating voids have had a different formation history, inducing significant changes on the halo occupation distribution.

Constraints on the growth of structure around cosmic voids in eBOSS DR14

We present catalogues of cosmic voids identified in the distribution of Luminous Red Galaxies (LRGs) and Quasi Stellar Objects (QSOs) in the fourteenth data release (DR14) of the extended Baryon Oscillation Spectroscopic Survey (eBOSS). We perform a multivariate analysis to assess the level of contamination in these catalogues by spurious Poisson underdensities. We find that the LRG void catalogue is largely free from contamination but that the QSO catalogue may be heavily contaminated. We analyse the multipoles of the void-galaxy cross-correlation function in these catalogues to obtain constraints on the growth rate of structure around voids. We find a value of β(z=0.703)=0.58+0.33−0.28 for the LRG voids and β(z=1.53)=0.15+0.13−0.12 for the QSO voids.

Spatial correlations of extended cosmological structures

ABSTRACT Studies of large-scale structures in the Universe, such as superstructures or cosmic voids, have been widely used to characterize the properties of the cosmic web through statistical analyses. On the other hand, the two-point correlation function of large-scale tracers such as galaxies or haloes provides a reliable statistical measure. However, this function applies to the spatial distribution of point-like objects, and therefore it is not appropriate for extended large structures that strongly depart from spherical symmetry. Here we present an analysis based on the standard correlation function formalism that can be applied to extended objects exhibiting arbitrary shapes. Following this approach, we compute the probability excess Ξ of having spheres sharing parts of cosmic structures with respect to a realization corresponding to a distribution of the same structures in random positions. For this aim, we identify superstructures defined as future virialized structures (FVSs) in semi-analytic galaxies in the MPDL2 MultiDark simulation. We have also identified cosmic voids to provide a joint study of their relative distribution with respect to the superstructures. Our analysis suggests that Ξ provides useful characterizations of the large-scale distribution, as suggested from an analysis of subsets of the simulation. Even when superstructure properties may exhibit negligible variations across the subsets, Ξ has the sensitivity to statistically distinguish sub-boxes that depart from the mean at larger scales. Thus, our methods can be applied in analysis of future surveys to provide characterizations of large-scale structure suitable to distinguish different theoretical scenarios.

The Gravitational Lensing Signatures of BOSS Voids in the Cosmic Microwave Background

Abstract We report a detection of the gravitational lensing effect of cosmic voids from the Baryon Oscillation Spectroscopic Data Release 12 seen in the Planck 2018 cosmic microwave background (CMB) lensing convergence map. To make this detection, we introduce new optimal techniques for void stacking and filtering of the CMB maps, such as binning voids by a combination of their observed galaxy density and size to separate those with distinctive lensing signatures. We calibrate theoretical expectations for the void lensing signal using mock catalogs generated in a suite of 108 full-sky lensing simulations from Takahashi et al. Relative to these templates, we measure the lensing amplitude parameter in the data to be A L = 1.10 ± 0.21 using a matched-filter stacking technique and confirm it using an alternative Wiener-filtering method. We demonstrate that the result is robust against thermal Sunyaev–Zel’dovich contamination and other sources of systematics. We use the lensing measurements to test the relationship between the matter and galaxy distributions within voids and show that the assumption of linear bias with a value consistent with galaxy clustering results is discrepant with observation at ∼3σ; we explain why such a result is consistent with simulations and previous results, and is expected as a consequence of void selection effects. We forecast the potential for void CMB lensing measurements in future data from the Advanced ACT, Simons Observatory, and CMB-S4 experiments, showing that, for the same number of voids, the achievable precision improves by a factor of more than 2 compared to Planck.