Mass determination of groups of galaxies: Effects of the cosmological constant
Abstract
The spherical infall model first developed by Lemaıˆtre and Tolman was modified in order to include the effects of a dark energy term. The resulting velocitydistance relation was evaluated numerically. This equation, when fitted to actual data, permits the simultaneous evaluation of the central mass and of the Hubble parameter. Application of this relation to the Local Group, when the dark energy is modeled by a cosmological constant, yields a total mass for the M31Milky Way pair of (2.5 ± 0.7) × 10^{12}M_{☉}, a Hubble parameter H_{0} = 74 ± 4 km s^{1} Mpc^{1} and a 1D velocity dispersion for the flow of about 39 km s^{1}. The zerovelocity and the marginally bound surfaces of the Local Group are at about 1.0 and 2.3 Mpc, respectively, from the center of mass. A similar analysis for the Virgo cluster yields a mass of (1.10 ± 0.12) × 10^{15}M_{☉} and H_{0} = 65 ± 9 km s^{1} Mpc^{1}. The zerovelocity is located at a distance of 8.6 ± 0.8 Mpc from the center of the cluster. The predicted peculiar velocity of the Local Group towards Virgo is about 190 km s^{1}, in agreement with other estimates. Slightly lower masses are derived if the dark energy is represented by a fluid with an equation of state P = w∊ with w = 2/3.
 Publication:

New Astronomy
 Pub Date:
 January 2006
 DOI:
 10.1016/j.newast.2005.08.008
 arXiv:
 arXiv:astroph/0508614
 Bibcode:
 2006NewA...11..325P
 Keywords:

 Local group;
 Virgo cluster;
 Hubble constant;
 98.62.Ck;
 98.65.Bv;
 98.65.Cw;
 Masses and mass distribution;
 Small and compact galaxy groups;
 Galaxy clusters;
 Astrophysics
 EPrint:
 13 pages, 3 figures. Version to appear in New Astronomy. Typing errors corrected in relation (1) and in percentage value in page 5