Dark matter distribution in the Coma cluster from galaxy kinematics: breaking the mass-anisotropy degeneracy

By E. Lokas, G. Mamon. 2003

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We study velocity moments of elliptical galaxies in the Coma cluster using Jeans equations. The dark matter distribution in the cluster is modelled by a generalized formula based upon the results of cosmological N-body simulations. Its inner slope (cuspy or flat), concentration and mass within the virial radius are kept as free parameters, as well as the velocity anisotropy, assumed independent of position. We show that the study of line-of-sight velocity dispersion alone does not allow us to constrain the parameters. By a joint analysis of the observed profiles of velocity dispersion and kurtosis, we are able to break the degeneracy between the mass distribution and velocity anisotropy. We determine the dark matter distribution at radial distances larger than 3 per cent of the virial radius and we find that the galaxy orbits are close to isotropic. Due to limited resolution, different inner slopes are found to be consistent with the data and we observe a strong degeneracy between the inner slope a and concentration c; the best-fitting profiles have the two parameters related with c = 19-9.6α. Our best-fitting Navarro-Frenk-White profile has concentration c = 9, which is 50 per cent higher than standard values found in cosmological simulations for objects of similar mass. The total mass within the virial radius of 2.9h - 1 70 Mpc is 1.4 x 10 1 5 h - 1 70 M O . (with 30 per cent accuracy), 85 per cent of which is dark. At this distance from the cluster centre, the mass-to-light ratio in the blue band is 351h 7 0 solar units. The total mass within the virial radius leads to estimates of the density parameter of the Universe. assuming that clusters trace the mass-to-light ratio and baryonic fraction of the Universe, with Ω 0 = 0.29 ′ 0.1.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/c3ce2e9db6924e37204ebb52bd0d0b95acdc272c

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Citations in the corpus

CLASH-VLT: The mass, velocity-anisotropy, and pseudo-phase-space density profiles of the z = 0.44 galaxy cluster MACS J1206.2-0847 (2013, methodology): “The analyses of the kinematics of individual clusters have found concentrations both in line (Łokas et al. 2006b; Rines & Diaferio 2006) and above the theoretical expectations (Łokas & Mamon 2003; Łokas et al. 2006a; Wojtak & Łokas 2007; Lemze et al. 2009; Wojtak & Łokas 2010; Abdullah et al. 2011).”
Dark matter in elliptical galaxies — II. Estimating the mass within the virial radius (2004, methodology): “One solution is to analyse the velocity profiles or at least the 4th order velocity moments (Merritt 1987; Rix & White 1992; Gerhard 1993; Łokas & Mamon 2003; Katgert, Biviano, & Mazure 2004).”
Constraints on dark matter annihilation in clusters of galaxies with the Fermi large area telescope (2010, methodology): “Based on the best-fit NFW profiles given in these works, the weak lensing measurements in [39] based on SDSS imaging and galaxy dynamics from [40] give J values a factor of 2 higher while the weak lensing measurements from [38] based on CFHT imaging give J a factor of two lower than the value quoted”
On the efficiency and reliability of cluster mass estimates based on member galaxies (2006, methodology): “This term may be used to define the total mass of a cluster within a radius of given overdensity, i.e. the ’virial radius’, typically the radius where the mean cluster mass density equals 100 or 200 times the Universe critical density (see, e.g., Łokas & Mamon 2003).”
Galaxy Masses: A Review (2013, background): “One promising alternative approach is to consider the variation with projected radius of the LOS velocity dispersion and kurtosis ( Lokas 2002; Lokas & Mamon 2003).”
MAMPOSSt: Modelling Anisotropy and Mass Profiles of Observed Spherical Systems – I. Gaussian 3D velocities (2012, background): “This was found to (partially) lift the mass-anisotropy degeneracy when applied to dwarf spheroidal galaxies (Łokas 2002) and the Coma cluster, (Łokas & Mamon 2003): the joint constraint of LOS velocity dispersion and kurtosis profiles allows the estimation of both the mass profile (i.e.,…”
The observed concentration–mass relation for galaxy clusters (2007, unknown): “…+8.1 −6.9 0.45 +2.76 −0.31 Voigt & Fabian (2006) Abell 1367 0.022 CM 16.9 5.46 21.9 6.11 Rines et al. (2003) Abell 1656 0.023 CM 10.0 11.2 13.1 12.9 Rines et al. (2003) LOSVD 7.0 11.8 ± 0.3 9.3 13.9 ± 4 Łokas & Mamon (2003) Abell 539 0.029 CM 14.7 3.63 19.0 4.09 Rines et al. (2003) Abell 2199…”
CATALOG OF ULTRA-DIFFUSE GALAXIES IN THE COMA CLUSTERS FROM SUBARU IMAGING DATA (2016, background): “…the orbit e = 0.5 (Penny et al. 2009), the pericenter distance R = 100 kpc (Koda et al. 2015), the cluster mass within the radius Mcl(R) ∼ 3 × 1013Me (Łokas & Mamon 2003), and a Petrosian radius of the dwarf rd ∼ 2.9 kpc (converted from re = 1.5 kpc, assuming an exponential profile) for a model…”