We investigate the possible presence of neutral hydrogen (HI) in intergalactic filaments at very low redshift ($z\sim 0.08$), by stacking a set of 274,712 2dFGRS galaxy pairs over 21-cm maps obtained with dedicated observations conducted with the Parkes radio telescope, over a total sky area of approximately 1,300 square degrees covering two patches in the northern and in the southern Galactic hemispheres. The stacking is performed by combining local maps in which each pair is brought to a common reference frame; the resulting signal from the edge galaxies is then removed to extract the filament residual emission. We repeat the analysis on maps cleaned removing either 10 or 20 foreground modes in a principal component analysis. Our study does not reveal any clear HI excess in the considered filaments in either case; we determine upper limits on the total filament HI brightness temperature at $T_{\rm b} \lesssim 10.3 \,μ\text{K}$ for the 10-mode and at $T_{\rm b} \lesssim 4.8 \,μ\text{K}$ for the 20-mode removed maps at the 95% confidence level. These estimates translate into upper limits for the local filament HI density parameter, $Ω_{\rm HI}^{\rm (f)} \lesssim 7.0\times10^{-5}$ and $Ω_{\rm HI}^{\rm (f)} \lesssim 3.2\times10^{-5}$ respectively, and for the HI column density, $N_{\rm HI} \lesssim 4.6\times10^{15}\,\text{cm}^{-2}$ and $N_{\rm HI} \lesssim 2.1\times10^{15}\,\text{cm}^{-2}$ respectively. These column density constraints are consistent with previous detections of HI in the warm-hot intergalactic medium obtained observing broad Ly $α$ absorption systems. The present work shows for the first time how such constraints can be achieved using the stacking of galaxy pairs on 21-cm maps.
Galaxy redshift surveys, such as 2dF, SDSS, 6df, GAMA and VIPERS, have shown that the spatial distribution of matter forms a rich web, known as the cosmic web. The majority of galaxy survey analyses measure the amplitude of galaxy clustering as a function of scale, ignoring information beyond a small number of summary statistics. Since the matter density field becomes highly non-Gaussian as structure evolves under gravity, we expect other statistical descriptions of the field to provide us with additional information. One way to study the non-Gaussianity is to study filaments, which evolve non…
Multiple modifications of general relativity (GR) have been proposed in the literature in order to understand the nature of the accelerated expansion of the Universe. However, thus far all the predictions of GR have been confirmed with constantly increasing accuracy. In this work, we study the imprints of a particular class of models -- "screened" modified gravity theories -- on cosmic filaments. We have utilized the $N$-body code ISIS/RAMSES to simulate the symmetron model and the Hu-Sawicky $f(R)$ model, and we post-process the output with DisPerSE to identify the filaments of the cosmic web…
The accretion of satellites onto central galaxies along vast cosmic filaments is an apparent outcome of the anisotropic collapse of structure in our Universe. Numerical work (based on gravitational dynamics of N-body simulations) indicates that satellites are beamed towards hosts along preferred directions imprinted by the velocity shear field. Here we use the Sloan Digital Sky Survey to observationally test this claim. We construct 3D filaments and sheets and examine the relative position of satellite galaxies. A statistically significant alignment between satellite galaxy position and filame…
Clusters of galaxies are at the intersection of cosmic filaments and are still accreting galaxies and groups along these preferential directions, but, because of their relatively low contrast on the sky, they are difficult to detect (unless a large amount of spectroscopic data are available), and unambiguous detections have been limited until now to relatively low redshifts (z<0.3). We searched for extensions and filaments around the thirty clusters of the DAFT/FADA survey (redshift range 0.4<z<0.9) with deep wide field photometric data. For each cluster, based on a colour-magnitude diagram, w…
We discover that the mass of dark matter particles mDM is imprinted in phase-correlations of the cosmic density field more significantly than in the 2-point correlation. In particular, phase-correlations trace mDM out to scales about five times larger than the 2-point correlation. This result relies on a new estimator l(r) of pure phase-information in Fourier space, which can be interpreted as a parameter-free and scale-invariant tracer of filament-like structure. Based on simulated density fields we show how mDM can, in principle, be measured using l(r), given a suitably reconstructed density…
Inspired by the study of mild transient reductions in the speed of sound of the adiabatic mode during inflation, we search for a primordial localized feature imprinted in cosmic microwave background and large-scale structure formation observables. We find some common oscillatory patterns both in the Planck CMB temperature-temperature power spectrum and the WiggleZ galaxy spectrum. By performing independent searches with these two data sets, we find a coincidence in the most significant mode previously found by Achúcarro et al. 2013 by using only Planck data. Furthermore, the joint data analysi…
We consider a universe with a non-classical stringy topology that has fixed points. We concentrate on the simplest example, an orbifold point, and study its observable imprints on the cosmic microwave background (CMB). We show that an orbifold preserves the Gaussian nature of the temperature fluctuations, yet modifies the angular correlation function. A direct signature of an orbifold is a single circle in the CMB that is invariant under rotation by 180 degrees. Searching the 7-year ILC map of WMAP, we find one candidate circle with high statistical significance. However, a closer look reveals…
Searching for signatures of self-interacting dark matter in halos from full-physics simulations: From 3D structure to projected observables
Università di Milano Bicocca（米兰比可卡大学）；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）；Donostia International Physics Center (DIPC)（圣塞巴斯蒂安国际物理中心）
We use a 64$h^{-1}$Mpc dark matter (DM) only cosmological simulation to examine the large scale orientation of haloes and substructures with respect the cosmic web. A web classification scheme based on the velocity shear tensor is used to assign to each halo in the simulation a web type: knot, filament, sheet or void. Using $\sim10^6$ haloes that span ~3 orders of magnitude in mass the orientation of the halo's spin and the orbital angular momentum of subhaloes with respect to the eigenvectors of the shear tensor is examined. We find that the orbital angular momentum of subhaloes tends to alig…
In hierarchical models of structure formation, the first galaxies form in low-mass dark matter potential wells, probing the behavior of dark matter on kiloparsec (kpc) scales. Even though these objects are below the detection threshold of current telescopes, future missions will open an observational window into this emergent world. In this Letter we investigate how the first galaxies are assembled in a `fuzzy' dark matter (FDM) cosmology where dark matter is an ultralight $\sim 10^{-22}$~eV boson and the primordial stars are expected to form along dense dark matter filaments. Using a first-of…
Matter distribution in the environment of galaxy clusters, from their cores to their connected cosmic filaments, must be in principle related to the underlying cluster physics and it evolutionary state. We aim to investigate how radial and azimuthal distribution of gas is affected by cluster environments, and how it can be related to cluster mass assembly history. Radial physical properties of gas (velocity, temperature, and density) is first analysed around 415 galaxy cluster environments from IllustrisTNG simulation at z = 0 (TNG300-1). Whereas hot plasma is virialised inside clusters (< R20…
We follow up on the surprising recent announcement by Vernstrom et al. (2021) of the detection of the synchrotron cosmic web. We attempt to reproduce their detection with new observations with the Phase II, extended configuration of the Murchison Widefield Array at \SI{118.5}{\mega \hertz}. We reproduce their detection methodology by stacking pairs of nearby luminous red galaxies (LRGs) -- used as tracers for clusters and galaxy groups -- contained in our low frequency radio observations. We show that our observations are significantly more sensitive than those used in Vernstrom et al., and th…
The impact of cosmic filaments on starburst galaxies across cosmic times
Observatoire Astronomique de Strasbourg, UMR 7550, CNRS, Université de Strasbourg（斯特拉斯堡天文台，法国国家科学研究中心，斯特拉斯堡大学）；Institut d’Astrophysique de Paris, UMR 7095, CNRS, Sorbonne Université（巴黎天体物理研究所，法国国家科学研究中心，索邦大学）；SRON Netherlands Institute for Space Research（荷兰空间研究所）；Kapteyn Astronomical Institute, University of Groningen（格罗宁根大学卡普坦天文研究所）；European Space Agency/ESTEC（欧洲空间局/欧洲空间研究与技术中心）；Leiden Observatory, Leiden University（莱顿大学莱顿天文台）；Aix Marseille Univ, CNRS, CNES, LAM（艾克斯-马赛大学，法国国家科学研究中心，法国国家太空研究中心）；The University of Texas at Austin（德克萨斯大学奥斯汀分校）；Department of Physics, University of California, Santa Barbara（加州大学圣塔芭芭拉分校物理系）；Cosmic Dawn Center (DAWN)（宇宙黎明中心）；Institute for Computational Cosmology, Department of Physics, Durham University（杜伦大学物理系计算宇宙学研究所）
The strikingly anisotropic large-scale distribution of matter made of an extended network of voids delimited by sheets, themselves segmented by filaments, within which matter flows towards compact nodes where they intersect, imprints its geometry on the dynamics of cosmic flows, ultimately shaping the distribution of galaxies and the redshift evolution of their properties. The (filament-type) saddle points of this cosmic web provide a local frame in which to quantify the induced physical and morphological evolution of galaxies on large scales. The properties of virtual galaxies within the Hori…
The imprints of massive neutrinos on the three-point correlation function of large-scale structures
Università di Bologna（博洛尼亚大学）；INAF–Osservatorio di Astrofisica e Scienza dello Spazio di Bologna（博洛尼亚天文物理与空间科学国家研究所）；INAF-Osservatorio Astronomico di Brera（布拉耶天文台国家研究所）；INFN-Sezione di Genova（热那亚意大利国家核物理研究所）；Dipartimento di Fisica, Università di Genova（热那亚大学物理系）
On the shape of pancakes: catastrophe theory and Gaussian statistics in 2D
Sorbonne Université（索邦大学）；CNRS（法国国家科学研究中心）；Institut d’Astrophysique de Paris（巴黎天体物理研究所）；Institute for Advanced Research, Nagoya University（名古屋大学高等研究院）；Kobayashi-Maskawa Institute for the Origin of Particles and the Universe, Nagoya University（名古屋大学小林-益川粒子起源与宇宙研究所）；Center for Gravitational Physics and Quantum Information, Yukawa Institute for Theoretical Physics, Kyoto University（京都大学汤川理论物理研究所引力物理与量子信息中心）；Kavli Institute for the Physics and Mathematics of the Universe (WPI), Todai institute for Advanced Study, University of Tokyo（东京大学东大高等研究院卡弗里宇宙物理数学研究所）
The quest for a B-mode imprint from primordial gravity waves on the polarization of the cosmic microwave background (CMB) requires the characterization of foreground polarization from Galactic dust. We present a statistical study of the filamentary structure of the 353 GHz Planck Stokes maps at high Galactic latitude, relevant to the study of dust emission as a polarized foreground to the CMB. We filter the intensity and polarization maps to isolate filaments in the range of angular scales where the power asymmetry between E-modes and B-modes is observed. Using the Smoothed Hessian Major Axis …
We introduce a multiscale topological description of the Megaparsec weblike cosmic matter distribution. Betti numbers and topological persistence offer a powerful means of describing the rich connectivity structure of the cosmic web and of its multiscale arrangement of matter and galaxies. Emanating from algebraic topology and Morse theory, Betti numbers and persistence diagrams represent an extension and deepening of the cosmologically familiar topological genus measure, and the related geometric Minkowski functionals. In addition to a description of the mathematical background, this study pr…
We calculate the expected imprint of the ionized gas in the Milky-Way halo on the Cosmic Microwave Background (CMB) through the kinetic Sunyaev-Zel'dovich (kSZ) effect. Unlike other Galactic foregrounds, the halo kSZ signature covers the full sky, generates anisotropies on large angular scales, is not accompanied by spectral distortions, and could therefore be confused with primordial CMB anisotropies. We construct theoretical models for various halo components, including smooth diffuse gas, filaments of cold inflowing gas and high velocity clouds. We find that the kSZ effect for all component…
About half of the baryons of the Universe are expected to be in the form of filaments of hot and low density intergalactic medium. Most of these baryons remain undetected even by the most advanced X-ray observatories which are limited in sensitivity to the diffuse low density medium. The Planck satellite has provided hundreds of detections of the hot gas in clusters of galaxies via the thermal Sunyaev-Zel'dovich (tSZ) effect and is an ideal instrument for studying extended low density media through the tSZ effect. In this paper we use the Planck data to search for signatures of a fraction of t…
Galaxies exhibit different clustering and quenching properties in clusters, filaments, and the field, but it is still uncertain whether such differences are imprints of the tidal environment on galaxy formation, or if they reflect the variation of the underlying halo mass function across the cosmic web. We measure the dependence of galaxy clustering and quenching on the cosmic web in the Sloan Digital Sky Survey, characterized by the combination of spherical overdensity $δ_8$ and tidal anisotropy $α_5$ centred on each galaxy. We find that galaxy clustering is a strong function of either $δ_8$ …
