Velocity correlation tensor and substructure's statistics around density peaks (original) (raw)

Dynamical Evolution of Clusters of Galaxies: The Effect of High-Velocity Substructure Clumps

International Journal of Modern Physics A, 2002

In the Cold Dark Matter (hereafter CDM) scenario even isolated density peaks contain a high fraction of small scale clumps having velocities larger than the average escape velocity from the structure. These clumps populate protoclusters, especially in the peripheral regions, r≥R f (where R f is the filtering scale). During the cluster collapse and the subsequent secondary infall, collapsing or infalling clumps (having vv esc . We study the interaction between these two kinds of clumps by means of the impulse approximation1 and we find that the collapse of bound clumps is accelerated with respect to the homogeneous case (Gunn and Gott's model, Ref. 2). The acceleration of the collapse increases with decreasing height of the peak, ν. We finally compare the acceleration produced by this effect to the slowing down effect produced by the gravitational interaction of the quadrupole moment of the system with the tidal field of the matter of the neighboring proto-clusters studied by Del...

Velocity dispersion of brightest cluster galaxies in cosmological simulations

Monthly Notices of the Royal Astronomical Society, 2021

Using the DIANOGA hydrodynamical zoom-in simulation set of galaxy clusters, we analyse the dynamics traced by stars belonging to the brightest cluster galaxies (BCGs) and their surrounding diffuse component, forming the intracluster light (ICL), and compare it to the dynamics traced by dark matter and galaxies identified in the simulations. We compute scaling relations between the BCG and cluster velocity dispersions and their corresponding masses (i.e. MmathrmBCGstarM_\mathrm{BCG}^{\star }MmathrmBCGstar–$\sigma _\mathrm{BCG}^{\star }$, M200–σ200, MmathrmBCGstarM_\mathrm{BCG}^{\star }MmathrmBCGstar–M200, and sigmamathrmBCGstar\sigma _\mathrm{BCG}^{\star }sigmamathrmBCGstar–σ200), we find in general a good agreement with observational results. Our simulations also predict sigmamathrmBCGstar\sigma _\mathrm{BCG}^{\star }sigmamathrmBCGstar–σ200 relation to not change significantly up to redshift z = 1, in line with a relatively slow accretion of the BCG stellar mass at late times. We analyse the main features of the velocity dispersion profiles, as traced by stars, dark matter, and galaxies. As a result,...

Velocity distributions in clusters of galaxies

Monthly Notices of The Royal Astronomical Society, 2006

We employ a high-resolution dissipationless N-body simulation of a galaxy cluster to investigate the impact of subhalo selection on the resulting velocity distributions. Applying a lower limit on the present bound mass of subhalos leads to high subhalo velocity dispersions compared to the diffuse dark matter (positive velocity bias) and to a considerable deviation from a Gaussian velocity distribution (kurtosis -0.6). However, if subhalos are required to exceed a minimal mass before accretion onto the host, the velocity bias becomes negligible and the velocity distribution is close to Gaussian (kurtosis -0.15). Recently it has been shown that the latter criterion results in subhalo samples that agree well with the observed number-density profiles of galaxies in clusters. Therefore we argue that the velocity distributions of galaxies in clusters are essentially un-biased. The comparison of the galaxy velocity distribution and the sound speed, derived from scaling relations of X-ray observations, results in an average Mach number of 1.24. Altogether 65% of the galaxies move supersonically and 8% have Mach numbers larger than 2 with respect to the intra cluster gas.

The mass function of galaxies based on correlated velocity structure

Monthly Notices of the Royal Astronomical Society, 1990

Summary This paper introduces a new approach to the calculation of the galactic mass multiplicity function based on the probability of correlated velocity structures existing on a given spatial scale. The correlations are supposed to have developed during a protogalactic era of virialized structures, before which time the density evolution had already become non-linear. We determine the density index empirically in this paper, although it may eventually be related to a spectrum of initial fluctuations. The subsequent non-linear dynamics are dealt with explicitly using a continuum model with tidal interactions simulated by an effective shear viscosity. Our predictions for the (unnormalized) mass function and for the large-scale velocity correlations between galaxies are deduced relatively directly from the ‘cosmic von Karman-Howarth’ equation implicit in our basic model. Our predictions are in good agreement with existing data. The first part of our paper offers a summary and a criti...