Kinematics of the local universe

Abstract

Abstract. The matter distribution around the Perseus-Pisces (PP) supercluster is studied by comparing peculiar velocities given by the Kinematics of the local universe (KLUN) galaxy sample to those predicted by Tolman-Bondi (TB) models. To restrict the TB solutions we first solve the mass of the densest part of PP. This part is identified as a sphere at (l, b) = (140.2• , −22.0Mpc having a radius of 15 h −1 Mpc. This sphere surrounds the main part of the PP ridge and four most prominent clusters of the region. Using virial-like mass estimators we calculate the cluster masses and obtain the upper and lower limits for the mass inside the 15 h −1 Mpc sphere: MPP = 4-7 h −1 10 15 M . This corresponds to a mass overdensity δPP ≈ 4, or ρPP = 1 -2 ρcr. Mass to light ratios of the clusters are M/L = 200 -600 h M /L , giving mass density ratio Ω0 = 0.1 -0.3, if the value of M/L is assumed to be representative elsewhere in the universe. We estimate a radial density distribution around the PP core using two toy models and a smoothed density distribution observed for IRAS galaxies. The cosmological density parameters (Ω0, ΩΛ) and the PP mass are free parameters in the TB calculations. The KLUN velocities, obtained by Tully-Fisher relation and the normalized distance method, are adjusted by the Local Group (LG) infall velocity towards PP. Comparison of the TB velocities to KLUN data points indicates that the infall velocity v inf < 100 km s −1 . Allowing MPP to vary within the limits given above we get constraints for the value of Ω0; Ω0 = 0.2-0.4 are prefered to the more extreme values, Ω0 = 0.1 or 1. A choice of either ΩΛ = 1 − Ω0 or 0 do not cause any significant changes in the results. The validity of the TB model in complex environments is studied with an N-body simulation. There we see that the radially averaged velocity fields around simulated clusters are compatible with the corresponding TB velocities. This confirms the applicability of the TB model around large galaxy concentrations, providing that smoothed density and radially averaged velocity fields are used.

On the quiescence of the Hubble flow in the vicinity of the Local Group

“…He also asked what happens when the distances become more accurate, in particular, will the velocity dispersion still decrease below σ v = 60 km s −1 which he derived from those data. We also note that Karachentsev & Makarov (1996) found that by using both massive and small galaxies the velocity dispersion in the local volume is σ v = 72 km s −1 .…”

Characteristic density contrasts in the evolution of superclusters. The case of A2142 supercluster

“…Einasto et al 2011a, for an analysis of supercluster morphology). The collapsing high-density cores have been studied in the very rich Shapley and Corona Borealis superclusters (Reisenegger et al 2000;Pearson et al 2014), in the Perseus-Pisces supercluster (Hanski et al 2001;Teerikorpi et al 2015), in the A2199 supercluster, the member of the Hercules supercluster (Rines et al 2002;Einasto et al 2001), and also in the richest supercluster of the Sloan Great Wall (Einasto et al 2007(Einasto et al , 2011bHeinämäki et al, in prep.). Chon et al (2015) analysed the Shapley supercluster with the future collapse model and concluded that only the central part of the Shapley supercluster will form a supercluster in the distant future.…”

The radius, at which a galaxy group stops the Hubble stream, and the group mass: an exact analytical solution

“…Some authors (e.g., (Karachentsev et al 2009)) use approximate formulas for M (R0). Now N-body simulations are frequently performed to obtain M (R0) (for example, (Hanski et al 2001;Peñarrubia et al 2014)). Of course, N-body simulations is a power method allowing to consider, e.g.…”