The Mass Profile of the Coma Galaxy Cluster

Abstract

We use a new redshift survey complete to within 4Њ .25 from the center of the Coma cluster to m Ӎ 15.4 R measure the mass profile of the cluster to h Ϫ1 Mpc. We extend the profile to h Ϫ1 Mpc with a r ∼ 5.5 r ∼ 10 further sample complete to in 42% of the area within a 10Њ radius and to in the remaining m ϭ 15.4 m ϭ 15.5 R Zw area. Galaxies within this region are falling onto the cluster on moderately radial orbits and thus do not satisfy virial equilibrium. Nonetheless, identification of the caustics in redshift space provides an estimate of the gravitational potential at radius r and hence of the system mass, Ϫ1M(≤ 10 h Mpc) ϭ (1.65 ‫ע‬ 0.41) # (1 j error). Previous mass estimates derived from optical and X-ray observations are limited to 15 Ϫ1 10 h M , h Ϫ1 Mpc. Our mass profile is consistent with these estimates but extends to distances 4 times as large. r ≤ 2.5 Over the entire range, the mass increases with r at the rate expected for a Navarro, Frenk, & White density profile.

The velocity field of collapsing spherical structures

“…The outer bar at 10 shows the estimation given by Geller et al (1999). Hughes (1989) determined the minimum and maximum mass profiles consistent with all the data for Coma -if the mass-to-light ratio of the data was not constrained to be a constant -obtaining allowed mass ranges of M 0.5 = 1.9-3.6 × 10 14 h −1 M and M 2.5 = 0.5-1.5 × 10 15 h −1 M where M 0.5 and M 2.5 are the masses inside 0.5 h −1 Mpc and 2.5 h −1 Mpc respectively.…”

“…The methods based on the form of the caustics in redshift space belong among others in this class. In a series of papers (Diaferio et al 1997;Diaferio 1999;Geller et al 1999), it has been proposed to estimate the mass profile of a galaxy cluster using the equation…”

“…These model functions for A are smooth and decreasing, as it required by Eqs. (8) and (9), and their approximation is based on the respective curves estimated by Geller et al (1999). …”

“…For this purpose, we employ data provided by Geller et al (1999). The largest sample presented by these authors contains 691 galaxies.…”

“…These curves, called caustics, form an envelope containing the galaxies of the cluster. The caustics are used to estimate the density parameter Ω 0 of the universe (Regös & Geller 1989) and the mass profile for the galaxy clusters (Geller et al 1999;Reisenegger et al 2000). In Sect.…”