Galaxy groups and clouds in the Local (z~0.01) universe

TL;DR

This paper presents an all-sky catalogue of 395 nearby galaxy groups within the Local universe, analyzing their properties, mass estimates, and the local matter density, revealing a lower Omega_m than the cosmic average.

Contribution

The study introduces a new all-sky galaxy group catalogue based on a specific group-finding algorithm and provides detailed properties and mass estimates of these groups.

Findings

Identified 395 galaxy groups with median radius 268 kpc.

Estimated local matter density Omega_m=0.08+-0.02.

Found that 54% of galaxies are in groups, accounting for 82% of K-band light.

Abstract

We present an all-sky catalogue of 395 nearby galaxy groups revealed in the Local Supercluster and its surroundings. The groups and their associations are identified among 10914 galaxies at |b|>15deg with radial velocities VLG<3500 km/s. Our group finding algorithm requires the group members to be located inside their zero-velocity surface. Hereby, we assume that individual galaxy masses are proportional to their total K-band luminosities, M/L_K=6 Msun/Lsun. The sample of our groups, where each group has n>=4 members, is characterized by the following medians: mean projected radius <R>=268 kpc, radial velocity dispersion sigma_V=74 km/s, K-band luminosity L_K=1.2x10^11 Lsun, virial and projected masses Mvir=2.4x10^12 and Mp=3.3x10^12 Msun, respectively. Accounting for measurement error reduces the median masses by 30 per cent. For 97 per cent of identified groups the crossing time does not exceed the cosmic time, 13.7 Gyr, having the median at 3.8 Gyr. We examine different properties of the groups, in particular, of the known nearby groups and clusters in Virgo and Fornax. About a quarter of our groups can be classified as fossil groups where the dominant galaxy is at least ten times brighter than the other group members. In total, our algorithm identifies 54 per cent of galaxies to be members of groups. Together with triple systems and pairs they gather 82 per cent of the K-band light in Local universe. We have obtained the local value of matter density to be Omega_m=0.08+-0.02 within a distance of ~40 Mpc assuming H0=73 km/s/Mpc. It is significantly smaller than the cosmic value, 0.28, in the standard lambdaCDM model. The discrepancy between the global and local quantities of Omega_m may be caused by the existence of Dark Matter component unrelated to the virial masses of galaxy systems.