Kinematics and Mass Profile of AWM 7

Abstract

We have measured 492 redshifts (311 new) in the direction of the poor cluster AWM~7 and have identified 179 cluster members (73 new). We use two independent methods to derive a self-consistent mass profile, under the assumptions that the absorption-line galaxies are virialized and that they trace an underlying Navarro, Frenk & White (1997) dark matter profile: (1) we fit such an NFW profile to the radial distribution of galaxy positions and to the velocity dispersion profile; (2) we apply the virial mass estimator to the cluster. With these assumptions, the two independent mass estimates agree to \sim 15% within 1.7 h^{-1} Mpc, the radial extent of our data; we find an enclosed mass \sim (3+-0.5)\times 10^{14} h^{-1} M_\odot. The largest potential source of systematic error is the inclusion of young emission-line galaxies in the mass estimate. We investigate the behavior of the surface term correction to the virial mass estimator under several assumptions about the velocity anisotropy profile, still within the context of the NFW model, and remark on the sensitivity of derived mass profiles to outliers. We find that one must have data out to a large radius in order to determine the mass robustly, and that the surface term correction is unreliable at small radii.Comment: LaTeX, 5 tables, 7 figures, appeared as 2000 AJ 119 44; typos and Eq. 9 corrected; results are unaffecte

Studying the dynamical properties of 20 nearby galaxy clusters

“…Accordingly, it has to add an additional term to called the surface pressure term, C ( r ). Thus the virial mass profile can be determined using the following expression: where σ(< r ) is the integrated three‐dimensional velocity dispersion within the radius r , σ v ( r ) is a projected velocity dispersion within that radius, and ρ( r ) is the density distribution (Koranyi & Geller 2000; Tustin, Geller & Kenyon 2001). For NFW density profile and for isotropic orbits of galaxies inside the cluster, Projected mass estimation: an alternative method, projected mass method, is discussed by many authors, e.g.…”

“…Depending on the virial mass profile, just within 1.5 Mpc h −1 to avoid the systematic error caused by the determination of the mass in the outer regions using virial theorem, we fit it with the NFW profile (see Table 5). Columns 1–4 are the scale radius, r s ; the mass within r s , M s ; the concentration parameter, c = r v / r s ; and the adjusted R ‐square, respectively (see NFW, Koranyi & Geller 2000). The scale radius, r s , of the studied sample has a mean value of 0.16 Mpc h −1 and ranges from 0.03 to 0.63 Mpc h −1 , while the mass within r s has a mean value of 6.7 × 10 13 M ⊙ and ranges from 1.25 × 10 13 to 16.5 × 10 13 M ⊙ .…”

“…where r s is the scale radius, M s = 4π δ s ρ s r 3 s [ln(2) − (1/2)] is the mass within r s , and δ s is the characteristic density (see Koranyi & Geller 2000;Rines et al 2003).…”

The Birmingham-CfA cluster scaling project - II. Mass composition and distribution

“…For this reason such studies are restricted to a small number of clusters (e.g. Fabricant, Kent & Kurtz 1989; Girardi et al 1995; Mohr et al 1996; Koranyi & Geller 2000, 2002). Given these limitations, we have taken a different approach to the issue of measuring the spatial distribution of galaxies and then estimating the total luminosity of the whole system.…”

The Pisces-Cetus supercluster: a remarkable filament of galaxies in the 2dF Galaxy Redshift and Sloan Digital Sky surveys

“…The mass within a radius r from the centre of the cluster can be derived from the modelled velocity dispersion and spatial density profiles λ( r ) (Koranyi & Geller 2000). On assumption of a constant mass‐to‐light ratio ϒ≡ M / L , the mass density ρ( r ) ≡ϒλ( r ), following , results in the enclosed mass profile, The core radius r c has already been found in the fitting of the surface brightness profile above.…”