Galaxy groups and clouds in the local (z̃ 0.01) Universe
Abstract
We present an allsky catalogue of 395 nearby galaxy groups revealed in the Local Supercluster and its surroundings. The groups and their associations are identified among 10 914 galaxies at b > 15° with radial velocities V_{LG} < 3500 km s^{1}. Our groupfinding algorithm requires the group members to be located inside their zerovelocity surface. Hereby, we assume that individual galaxy masses are proportional to their total Kband luminosities, M/L_{K}= 6 M_{☉}/L_{☉}.
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 σ_{V}= 74 km s^{1}, Kband luminosity L_{K}= 1.2 × 10^{11} L_{☉}, virial and projected masses M_{vir}= 2.4 × 10^{12} and M_{p}= 3.3 × 10^{12} M_{☉}, 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, with 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 10 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 Kband light in the local Universe. We have obtained the local value of matter density to be Ω_{m}= 0.08 ± 0.02 within a distance of ̃40 Mpc assuming H_{0}= 73 km s^{1} Mpc^{1}. It is significantly smaller than the cosmic value, 0.28, in the standard ΛCDM model. The discrepancy between the global and local quantities of Ω_{m} may be caused by the existence of a dark matter component unrelated to the virial masses of the galaxy systems.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 April 2011
 DOI:
 10.1111/j.13652966.2010.18071.x
 arXiv:
 arXiv:1011.6277
 Bibcode:
 2011MNRAS.412.2498M
 Keywords:

 catalogues;
 galaxies: groups: general;
 cosmological parameters;
 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 28 pages, 17 figures, accepted to MNRAS