When clusters of galaxies are viewed in projection, one cannot avoid picking up foreground/background interlopers (FBIs), that lie within the virial cone (VC), but outside the virial sphere. Structural & kinematic deprojection equations are not known for an expanding Universe, where the Hubble flow (HF) stretches the line-of-sight (LOS) distribution of velocities. We analyze 93 mock relaxed clusters, built from a cosmological simulation. The stacked mock cluster is well fit by an m=5 Einasto DM density profile (but only out to 1.5 virial radii [r_v]), with velocity anisotropy (VA) close to the Mamon-Lokas model with VA radius equal to that of density slope -2. The surface density of FBIs is nearly flat out to r_v, while their LOS velocity distribution shows a dominant gaussian cluster-outskirts component and a flat field component. This distribution of FBIs in projected phase space is nearly universal in mass. A local k=2.7 sigma velocity cut returns the LOS velocity dispersion profile (LOSVDP) expected from the NFW density and VA profiles measured in 3D. The HF causes a shallower outer LOSVDP that cannot be well matched by the Einasto model for any k. After this velocity cut, FBIs still account for 23% of DM particles within the VC (close to the observed fraction of cluster galaxies lying off the Red Sequence). The best-fit projected NFW/Einasto models underestimate the 3D concentration by 6+/-6% (16+/-7%) after (before) the velocity cut, unless a constant background is included in the fit. Assuming the correct mass profile, the VA profile is well recovered from the measured LOSVDP, with a slight bias towards more radial orbits in the outer regions. These small biases are overshadowed by large cluster-cluster variations caused by cosmic variance. An appendix provides an analytical approximation to the surface density, projected mass and tangential shear profiles of the Einasto model.
We study dynamical mass measurements of galaxy clusters contaminated by interlopers and show that a modern machine learning (ML) algorithm can predict masses by better than a factor of two compared to a standard scaling relation approach. We create two mock catalogs from Multidark's publicly available $N$-body MDPL1 simulation, one with perfect galaxy cluster membership information and the other where a simple cylindrical cut around the cluster center allows interlopers to contaminate the clusters. In the standard approach, we use a power-law scaling relation to infer cluster mass from galaxy …
Combining our knowledge of halo structure and internal kinematics from cosmological dark matter simulations and the distribution of halo interlopers in projected phase space measured in cosmological galaxy simulations, we develop MAGGIE, a prior- and halo-based, probabilistic, abundance matching (AM) grouping algorithm for doubly complete subsamples (in distance and luminosity) of flux-limited samples. We test MAGGIE-L and MAGGIE-M (in which group masses are derived from AM applied to the group luminosities and stellar masses, respectively) on groups of at least three galaxies extracted from a…
The 3D radial escape-velocity profile of galaxy clusters has been suggested to be a promising and competitive tool for constraining mass profiles and cosmological parameters in an accelerating universe. However, the observed line-of-sight escape profile is known to be suppressed compared to the underlying 3D radial (or tangential) escape profile. Past work has suggested that velocity anisotropy in the phase-space data is the root cause. Instead, we find that the observed suppression is from the statistical undersampling of the phase spaces and that the 3D radial escape edge can be accurately i…
We present a simulation-based inference framework using a convolutional neural network to infer dynamical masses of galaxy clusters from their observed 3D projected phase-space distribution, which consists of the projected galaxy positions in the sky and their line-of-sight velocities. By formulating the mass estimation problem within this simulation-based inference framework, we are able to quantify the uncertainties on the inferred masses in a straightforward and robust way. We generate a realistic mock catalogue emulating the Sloan Digital Sky Survey (SDSS) Legacy spectroscopic observations…
Galaxy-galaxy strong gravitational lenses have become a popular probe of dark matter (DM) by providing a window into structure formation on the smallest scales. In particular, the convergence power spectrum of subhalos within lensing galaxies has been suggested as a promising observable to study DM. However, the distances involved in strong-lensing systems are vast, and we expect the relevant volume to contain line-of-sight (LOS) halos that are not associated with the main lens. We develop a formalism to calculate the effect of LOS halos as an effective convergence power spectrum. The multi-le…
Studies of cluster mass and velocity anisotropy profiles are useful tests of dark matter models, and of the assembly history of clusters of galaxies. These studies might be affected by unknown systematics caused by projection effects. We aim at testing observational methods for the determination of mass and velocity anisotropy profiles of clusters of galaxies. Particularly, we focus on the MAMPOSSt technique (Mamon et al. 2013). We use results from two semi-analytic models of galaxy formation coupled with high-resolution N-body cosmological simulations, the catalog of De Lucia & Blaizot (2007)…
We present an algorithm for inferring the dynamical mass of galaxy clusters directly from their respective phase-space distributions, i.e. the observed line-of-sight velocities and projected distances of galaxies from the cluster centre. Our method employs normalizing flows, a deep neural network capable of learning arbitrary high-dimensional probability distributions, and inherently accounts, to an adequate extent, for the presence of interloper galaxies which are not bounded to a given cluster, the primary contaminant of dynamical mass measurements. We validate and showcase the performance o…
We present a Bayesian hierarchical inference formalism (Basilisk) to constrain the galaxy-halo connection using satellite kinematics. Unlike traditional methods, Basilisk does not resort to stacking the kinematics of satellite galaxies in bins of central luminosity, and does not make use of summary statistics, such as satellite velocity dispersion. Rather, Basilisk leaves the data in its raw form and computes the corresponding likelihood. In addition, Basilisk can be applied to flux-limited, rather than volume-limited samples, greatly enhancing the quantity and dynamic range of the data. And f…
Observational Evidence of Velocity Anisotropy Assembly Bias in Galaxy Clusters
CONICET. Instituto de Astronomía Teórica y Experimental (IATE)（阿根廷国家科学研究委员会理论与实验天体物理研究所）；Universidad Nacional de Córdoba (UNC). Observatorio Astronómico de Córdoba (OAC)（科尔多瓦国立大学科尔多瓦天文台）；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）；IFPU Institute for Fundamental Physics of the Universe（宇宙基础物理研究所）；Centre for Particle Cosmology, University of Pennsylvania（宾夕法尼亚大学粒子宇宙学中心）；Departamento de Física, Universidad Técnica Federico Santa María（智利费德里科·Santa María理工大学物理系）
We present a formalism that incorporates hydrogen Lyman-alpha (Ly$α$) polarization arising from the scattering of radiation in galaxy halos into the intensity mapping approach. Using the halo model, and emission profiles based on simulations and observations, we calculate auto and cross power spectra at redshifts $3\leq z \leq13$ for the Ly$α$ total intensity, $I$, polarized intensity, $P$, degree of polarization, $Π=P/I$, and two new quantities, the astrophysical $E$ and $B$ modes of Ly$α$ polarization. The one-halo terms of the $Π$ power spectra show a turnover that signals the average exten…
The kinematic Sunyaev-Zel'dovich (kSZ) effect --- the Doppler boosting of cosmic microwave background (CMB) photons due to Compton-scattering off free electrons with non-zero bulk velocity --- probes the abundance and distribution of baryons in the Universe. All kSZ measurements to date have explicitly required spectroscopic redshifts. Here, we implement a novel estimator for the kSZ -- large-scale structure cross-correlation based on projected fields: it does not require redshift estimates for individual objects, allowing kSZ measurements from large-scale imaging surveys. We apply this estima…
We investigate the three-point correlation function (3PCF) in the squeezed limit by considering galaxy pairs as discrete objects and cross-correlating them with the galaxy field. We develop an efficient algorithm using Fast Fourier Transforms to compute such cross-correlations and their associated pair-galaxy bias bpg and the squeezed 3PCF coefficient Qeff. We implement our method using N-body cosmological simulations and a fiducial Halo Occupation Distribution (HOD) and present the results in both the real space and redshift space. In real space, we observe a peak in bpg and Qeff at pair sepa…
Forthcoming large-scale spectroscopic surveys will soon provide data on thousands of galaxy clusters. It is important that the systematics of the various mass estimation techniques are well understood and calibrated. We compare three different dynamical mass estimators using the C-EAGLE galaxy clusters, a set of high resolution simulations with resolved galaxies a median total mass, $M_{200c} = 10^{14.7} \, \mathrm{M_\odot}$. We quantify the bias and scatter of the Jeans, virial, and caustic mass estimators using all galaxies with a stellar mass $M_*> 10^9 \, \mathrm{M_\odot}$, both in the ide…
CLASH-VLT: The variance in the velocity anisotropy profiles of galaxy clusters
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）；IFPU-Institute for Fundamental Physics of the Universe（宇宙基础物理研究所）；Dipartimento di Fisica, Università degli Studi di Milano（米兰大学物理系）；Dipartimento di Fisica G. Occhialini, Università degli Studi di Milano-Bicocca（米兰比可卡大学G.奥恰利尼物理系）；Department of Physics and Earth Sciences, University of Ferrara（费拉拉大学物理与地球科学系）；Dipartimento di Fisica E. R. Caianiello, Università Degli Studi di Salerno（萨莱诺大学E.R.凯亚涅洛物理系）；INAF – Osservatorio Astronomico di Capodimonte（意大利国家天体物理研究所卡波迪蒙特天文台）
