More than half of the volume of our Universe is occupied by cosmic voids. The lensing magnification effect from those under-dense regions is generally thought to give a small dimming contribution: objects on the far side of a void are supposed to be observed as slightly smaller than if the void were not there, which together with conservation of surface brightness implies net reduction in photons received. This is predicted by the usual weak lensing integral of the density contrast along the line of sight. We show that this standard effect is swamped at low redshifts by a relativistic Doppler term that is typically neglected. Contrary to the usual expectation, objects on the far side of a void are brighter than they would be otherwise. Thus the local dynamics of matter in and near the void is crucial and is only captured by the full relativistic lensing convergence. There are also significant nonlinear corrections to the relativistic linear theory, which we show actually under-predicts the effect. We use exact solutions to estimate that these can be more than 20% for deep voids. This remains an important source of systematic errors for weak lensing density reconstruction in galaxy surveys and for supernovae observations, and may be the cause of the reported extra scatter of field supernovae located on the edge of voids compared to those in clusters.
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…
We investigate the potential of weak lensing by voids to test for deviations from General Relativity. We calculate the expected lensing signal of a scalar field with derivative couplings, finding that it has the potential to boost the tangential shear both within and outside the void radius. We use voids traced by Luminous Red Galaxies in SDSS to demonstrate the methodology of testing these predictions. We find that the void central density parameter, as inferred from the lensing signal, can shift from its GR value by up to 20% in some galileon gravity models. Since this parameter can be estim…
We study the prospects for measuring the dark matter distribution of voids with stacked weak lensing. We select voids from a large set of $N$-body simulations, and explore their lensing signals with the full ray-tracing simulations including the effect of the large-scale structure along the line-of-sight. The lensing signals are compared with simple void model predictions to infer the three-dimensional mass distribution of voids. We show that the stacked weak lensing signals are detected at significant level (S/N$\geq5$) for a 5000 degree$^2$ survey area, for a wide range of void radii up to $…
We study lensing by voids in Cubic Galileon and Nonlocal gravity cosmologies, which are examples of theories of gravity that modify the lensing potential. We find voids in the dark matter and halo density fields of N-body simulations and compute their lensing signal analytically from the void density profiles, which we show are well fit by a simple analytical formula. In the Cubic Galileon model, the modifications to gravity inside voids are not screened and they approximately double the size of the lensing effects compared to GR. The difference is largely determined by the direct effects of t…
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 report the first measurement of the diminutive lensing signal arising from matter underdensities associated with cosmic voids. While undetectable individually, by stacking the weak gravitational shear estimates around 901 voids detected in SDSS DR7 by Sutter et al. (2012a), we find substantial evidence for a depression of the lensing signal compared to the cosmic mean. This depression is most pronounced at the void radius, in agreement with analytical models of void matter profiles. Even with the largest void sample and imaging survey available today, we cannot put useful constraints on the…
Cosmic voids are a key component of the large-scale structure that contain a plethora of cosmological information. Typically, voids are identified from the underlying galaxy distribution, which is a biased tracer of the total matter field. Previous works have shown that 2D voids identified in weak lensing maps -- weak lensing voids -- correspond better to true underdense regions along the line of sight. In this work, we study how the properties of weak lensing voids depend on the choice of void finder, by adapting several popular void finders. We present and discuss the differences between ide…
The upcoming new generation of spectroscopic galaxy redshift surveys will provide large samples of cosmic voids, the distinct, large underdense structures in the universe. Combining these with future galaxy imaging surveys, we study the prospects of probing the underlying matter distribution in and around cosmic voids via the weak gravitational lensing effects of stacked voids, utilizing both shear and magnification information. The statistical precision is greatly improved by stacking together a large number of voids along different lines of sight, even when taking into account the impact of …
We have searched for the signature of cosmic voids in the CMB, in both the Planck temperature and lensing-convergence maps; voids should give decrements in both. We use zobov voids from the DR12 SDSS CMASS galaxy sample. We base our analysis on N-body simulations, to avoid a posteriori bias. For the first time, we detect the signature of voids in CMB lensing: the significance is $3.2σ$, close to $Λ$CDM in both amplitude and projected density-profile shape. A temperature dip is also seen, at modest significance ($2.3σ$), with amplitude about 6 times the prediction. This temperature signal is in…
We report a $5.3σ$ detection of the gravitational lensing effect of cosmic voids from the Baryon Oscillation Spectroscopic (BOSS) 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 l…
An essential aspect of cosmic voids is that these underdense regions provide complementary information about the properties of our Universe. Unlike dense regions, voids are avoided by matter and are less contaminated by baryonic processes. The first step to understanding the properties of cosmic voids is to correctly infer their mass profiles. In the literature, various techniques have been implemented. In this paper, we review them and implement a new technique that is based on Doppler lensing. We use a relativistic $N$-body code, \textsc{Gevolution}, to generate cosmological mass perturbatio…
We measure weak lensing mass profiles of voids from a volume-limited sample of SDSS Luminous Red Galaxies (LRGs). We find voids using an algorithm designed to maximize the lensing signal by dividing the survey volume into 2D slices, and then finding holes in this 2D distribution of LRGs. We perform a stacked shear measurement on about 20,000 voids with radii between 15-55 Mpc/h and redshifts between 0.16-0.37. We measure the characteristic radial shear signal of voids with a signal-to-noise of 7. The mass profile corresponds to a fractional underdensity of about -0.4 inside the void radius and…
We use the lensing potential map from Planck CMB lensing reconstruction analysis and the "Public Cosmic Void Catalog" to measure the stacked void lensing potential. In this profile, four parameters are needed to describe the shape of voids with different characteristic radii $R_V$. However, we have found that after reducing the background noise by subtracting the average background, there is a residue lensing power left in the data. The inclusion of the environment shifting parameter, $γ_V$, is necessary to get a better fit to the data with the residue lensing power. We divide the voids into t…
Lensing the darkness: The matter density profile in cosmic voids from UNIONS
University of Waterloo（滑铁卢大学）；Waterloo Centre for Astrophysics, University of Waterloo（滑铁卢大学水天体物理中心）；Perimeter Institute for Theoretical Physics（理论物理前沿研究所）；Università di Trieste（的里雅斯特大学）；INAF-Osservatorio Astronomico di Trieste（意大利国家天体物理研究所的里雅斯特天文台）；Institute for Astronomy, University of Hawaii（夏威夷大学天文学研究所）
Constraining Neutrino Mass with the Void Weak Lensing Effect
Tsinghua University（清华大学）；Shanghai Astronomical Observatory (SHAO)（上海天文台）；University of Chinese Academy of Sciences（中国科学院大学）；École Polytechnique Fédérale de Lausanne (EPFL)（洛桑联邦理工学院）
We study cosmic voids in the normal-branch Dvali-Gabadadze-Porrati (nDGP) braneworld models, which are representative of a class of modified gravity theories where deviations from General Relativity are usually hidden by the Vainshtein screening in high-density environments. This screening is less efficient away from these environments, which makes voids ideally suited for testing this class of models. We use N-body simulations of $Λ$-cold dark matter ($Λ$CDM) and nGDP universes, where dark matter haloes are populated with mock galaxies that mimic the clustering and number densities of the BOS…
We have used an exact general relativistic model structure within a FRW cosmological background based on a LTB metric to study the gravitational lensing of a cosmological structure. The integration of the geodesic equations turned out to be a delicate task. We realized that the use of the rank 8(7) and 10(11) Runge-Kutta numerical method leads to a numerical effect and is therefore unreliable. The so-called semi-implicit Rosenbrock method, however, turned out to be a viable integration method for our problem. The deviation angle calculated by the integration of the geodesic equations for diffe…
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）
Upcoming surveys such as \LSST{} and \Euclid{} will significantly improve the power of weak lensing as a cosmological probe. To maximise the information that can be extracted from these surveys, it is important to explore novel statistics that complement standard weak lensing statistics such as the shear-shear correlation function and peak counts. In this work, we use a recently proposed weak lensing observable -- weak lensing voids -- to make parameter constraint forecasts for an LSST-like survey. We use the \cosmoslics{} $w$CDM simulation suite to measure void statistics as a function of cos…
Towards precision cosmology with Void x CMB correlations (II): Impact of mock catalogs on the Void x CMB lensing signal
Instituto de Astrofísica de Canarias（加那利群岛天体物理研究所）；Universidad de La Laguna（拉戈纳大学）；MTA–CSFK Lendület “Momentum” Large-Scale Structure (LSS) Research Group（匈牙利科学院-塞格德大学“动量”大尺度结构研究组）；Konkoly Observatory, HUN-REN Research Centre for Astronomy and Earth Sciences（孔科利天文台，匈牙利研究与创新网络地球与天文学研究中心）；CPPM, Aix-Marseille Université, CNRS/IN2P3（地中海粒子与核物理中心，艾克斯-马赛大学，法国国家科学研究中心/法国国家核与粒子物理研究所）；Princeton University（普林斯顿大学）；California Institute of Technology（加州理工学院）
研究通过分析模拟目录对Void x CMB引力透镜信号的影响，探讨了未来宇宙学约束的潜力，发现该信号对模拟目录的依赖性较低，预计罗马任务结合现有和未来CMB观测将显著提高信号噪声比。
We present a simple gravitational lens model to illustrate the ease of using the embedded lensing theory when studying cosmic voids. It confirms the previously used repulsive lensing models for deep voids. We start by estimating magnitude fluctuations and weak lensing shears of background sources lensed by large voids. We find that sources behind large ($\sim$$90\,\rm Mpc$) and deep voids (density contrast about $-0.9$) can be magnified or demagnified with magnitude fluctuations of up to $\sim$$0.05\,\rm mag$ and that the weak-lensing shear can be up to the $\sim$$10^{-2}$ level in the outer r…
Dark matter halos represent the highest density peaks in the matter distribution. Conversely, cosmic voids are under-dense patches of the universe. Probing the mass distribution of the universe requires various approaches, including weak gravitational lensing that subtly modifies the shape of distant sources, and Doppler lensing that changes the apparent size and magnitude of objects due to peculiar velocities. In this work, we adopt both gravitational and Doppler lensing effects to study the underlying matter distribution in and around cosmic voids/halos. We use the relativistic $N$-body code…
We investigate void properties in $f(R)$ models using N-body simulations, focusing on their differences from General Relativity (GR) and their detectability. In the Hu-Sawicki $f(R)$ modified gravity (MG) models, the halo number density profiles of voids are not distinguishable from GR. In contrast, the same $f(R)$ voids are more empty of dark matter, and their profiles are steeper. This can in principle be observed by weak gravitational lensing of voids, for which the combination of a spectroscopic redshift and a lensing photometric redshift survey over the same sky is required. Neglecting th…
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 study the fluctuations in luminosity distances due to gravitational lensing by large scale (> 35 Mpc) structures, specifically voids and sheets. We use a simplified "Swiss cheese" model consisting of a Λ-CDM Friedman-Robertson-Walker background in which a number of randomly distributed non-overlapping spherical regions are replaced by mass compensating comoving voids, each with a uniform density interior and a thin shell of matter on the surface. We compute the distribution of magnitude shifts using a variant of the method of Holz & Wald (1998), which includes the effect of lensing shear. T…
The "Cold Spot" in the CMB sky could be due to the presence of an anomalous huge spherical underdense region - a "Void" - of a few hundreds Mpc/h radius. Such a structure would have an impact on the CMB two-point (power spectrum) and three-point (bispectrum) correlation functions not only at low-l, but also at high-l through Lensing, which is a unique signature of a Void. Modeling such an underdensity with an LTB metric, we show that for the power spectrum the effect should be visible already in the WMAP data only if the Void radius is at least L \gtrsim 1 Gpc/h, while it will be visible by th…
Galaxies and their dark matter halos populate a complicated filamentary network around large, nearly empty regions known as cosmic voids. Cosmic voids are usually identified in spectroscopic galaxy surveys, where 3D information about the large-scale structure of the Universe is available. Although an increasing amount of photometric data is being produced, its potential for void studies is limited since photometric redshifts induce line-of-sight position errors of $\sim50$ Mpc/$h$ or more that can render many voids undetectable. In this paper we present a new void finder designed for photometr…
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 MICE N-body simulation to calibrate our detection strategy for a given void definition and galaxy tracer density. We then identify cosmic voids in 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 im…
The Euclid space telescope will survey a large dataset of cosmic voids traced by dense samples of galaxies. In this work we estimate its expected performance when exploiting angular photometric void clustering, galaxy weak lensing and their cross-correlation. To this aim, we implement a Fisher matrix approach tailored for voids from the Euclid photometric dataset and present the first forecasts on cosmological parameters that include the void-lensing correlation. We examine two different probe settings, pessimistic and optimistic, both for void clustering and galaxy lensing. We carry out forec…
The anomaly in the Cosmic Microwave Background known as the "Cold Spot" could be due to the existence of an anomalously large spherical (few hundreds Mpc/h radius) underdense region, called a "Void" for short. Such a structure would have an impact on the CMB also at high multipoles l through Lensing. This would then represent a unique signature of a Void. Modeling such an underdensity with an LTB metric, we show that the Lensing effect leads to a large signal in the non-diagonal two-point function, centered in the direction of the Cold Spot, such that the Planck satellite will be able to confi…
The CMB lensing signal from cosmic voids and superclusters probes the growth of structure in the low-redshift cosmic web. In this analysis, we cross-correlated the Planck CMB lensing map with voids detected in the Dark Energy Survey Year 3 (Y3) data set ($\sim$5,000 deg$^{2}$), expanding on previous measurements that used Y1 catalogues ($\sim$1,300 deg$^{2}$). Given the increased statistical power compared to Y1 data, we report a $6.6σ$ detection of negative CMB convergence ($κ$) imprints using approximately 3,600 voids detected from a redMaGiC luminous red galaxy sample. However, the measured…
We explore voids in dark matter and halo fields from simulations of $Λ$CDM and Hu-Sawicki $f(R)$ models. In $f(R)$ gravity, dark matter void abundances are greater than that of general relativity (GR). However, when using haloes to identify voids, the differences of void abundances become much smaller, but can still be told apart, in principle, at the 2, 6 and 14 $σ$ level for the $f(R)$ model parameter amplitudes of $|f_{R0}|=10^{-6}$, $10^{-5}$ and $10^{-4}$. In contrast, the abundance of large voids found using haloes in $f(R)$ gravity is lower than in GR. The more efficient halo formation …
We present a new summary statistic for weak lensing observables, higher than second order, suitable for extracting non-Gaussian cosmological information and inferring cosmological parameters. We name this statistic the 'starlet $\ell_1$-norm' as it is computed via the sum of the absolute values of the starlet (wavelet) decomposition coefficients of a weak lensing map. In comparison to the state-of-the-art higher-order statistics -- weak lensing peak counts and minimum counts, or the combination of the two -- the $\ell_1$-norm provides a fast multi-scale calculation of the full void and peak di…
A local void modifies the sky distribution pattern of the cosmic microwave background (CMB) polarisation by gravitational lensing and produces B-modes from E-modes for an off-center observer. In order to see whether this effect can be used to observationally test the validity of the local void model, we calculate this lensing effect by solving the propagation of CMB polarisation along null geodesics close to the central light cone in the general Lemaître-Tolman-Bondi (LTB) model perturbatively. In particular, we give general formulas for the correlations of E and B observed by an off-center ob…
An extremely large void and a cosmic texture are two possible explanations for the cold spot seen in the cosmic microwave background. We investigate how well these two hypotheses can be tested with weak lensing of 21-cm fluctuations from the epoch of reionization (EoR) measured with the Square Kilometer Array (SKA). While the void explanation for the cold spot can be tested with SKA, given enough observation time, the texture scenario requires significantly prolonged observations, at the highest frequencies that correspond to the EoR, over the field of view containing the cold spot.
We derive the Fermat potential for a spherically symmetric lens embedded in an FLRW cosmology and use it to investigate the late-time integrated Sachs-Wolfe (ISW) effect, i.e., secondary temperature fluctuations in the cosmic microwave background (CMB) caused by individual large scale clusters and voids. We present a simple analytical expression for the temperature fluctuation in the CMB across such a lens as a derivative of the lens' Fermat potential. This formalism is applicable to both linear and nonlinear density evolution scenarios, to arbitrarily large density contrasts, and to all open …
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 an exact general relativistic model structure within an FRW cosmological background based on a LTB metric to study the gravitational lensing by a cosmological and dynamical structure. Using different density profiles for the model structure, the deviation angle and the time delay through the gravitational lensing has been studied by solving the geodesic equations. The results of these exact calculations have been compared to the thin lens approximation. We have shown that the result for the thin lens approximation based on a modified NFW density profile with a void before going over to …
How do peculiar velocities affect observed voids? To answer this question we use the VIDE toolkit to identify voids in mock galaxy populations embedded within an N-body simulation both with and without peculiar velocities included. We compare the resulting void populations to assess the impact on void properties. We find that void abundances and spherically-averaged radial density profiles are mildly affected by peculiar velocities. However, peculiar velocities can distort by up to 10% the shapes for a particular subset of voids depending on the void size and density contrast, which can lead t…
The properties of the cosmic microwave background (CMB) temperature and polarisation anisotropies measured by a static, off-centered observer located in a local spherically symmetric void, are described. In particular in this paper we compute, together with the standard 2- point angular correlation functions, the off-diagonal correlators, which are no more vanishing by symmetry. While the energy shift induced by the off-centered position of the observer can be suppressed by a proper choice of the observer velocity, a lensing-like effect on the CMB emission point remains. This latter effect is …
Impact of galaxy intrinsic alignments on non-Gaussian weak lensing statistics for modified gravity
LMU Faculty of Physics（慕尼黑大学物理学院）；Birla Institute of Technology and Science Pilani, Hyderabad Campus（比拉尔理工学院皮拉尼校区海得拉巴分校）；Newcastle University（纽卡斯尔大学）；Durham University（杜伦大学）；Max-Planck-Institut für Astronomie（马克斯·普朗克天文学研究所）；Indian Institute of Science Education and Research - Kolkata（印度科学教育与研究学院-加尔各答）
Cosmic voids offer an extraordinary opportunity to study the effects of massive neutrinos on cosmological scales. Because they are freely streaming, neutrinos can penetrate the interior of voids more easily than cold dark matter or baryons, which makes their relative contribution to the mass budget in voids much higher than elsewhere in the Universe. In simulations it has recently been shown how various characteristics of voids in the matter distribution are affected by neutrinos, such as their abundance, density profiles, dynamics, and clustering properties. However, the tracers used to ident…
Low density regions are less affected by the nonlinear structure formation and baryonic physics. They are ideal places for probing the nature of dark energy, a possible explanation for the cosmic acceleration. Unlike void lensing, which requires identifications of individual voids, we study the stacked lensing signals around the low-density-positions (LDP), defined as places that are devoid of foreground bright galaxies in projection. The method allows a direct comparison with numerical results by drawing correspondence between the bright galaxies with halos. It leads to lensing signals that a…
Doppler lensing is the apparent change in object size and magnitude due to peculiar velocities. Objects falling into an overdensity appear larger on its near side, and smaller on its far side, than typical objects at the same redshifts. This effect dominates over the usual gravitational lensing magnification at low redshift. Doppler lensing is a promising new probe of cosmology, and we explore in detail how to utilize the effect with forthcoming surveys. We present cosmological simulations of the Doppler and gravitational lensing effects based on the Millennium simulation. We show that Doppler…
