Dark matter halos around isolated ellipticals

¹ INFN-Istituto Nazionale di Fisica Nucleare, Sezione di Milano Bicocca, Piazza della Scienza 3, 20126 Milano, Italy
² INAF-Istituto Nazionale di Astrofisica, Osservatorio Astronomico di Brera, via Brera 28, 20121 Milano, Italy
e-mail: elisabetta.memola@mib.infn.it
³ SISSA/ISAS, via Bonomea 265, 34136 Trieste, Italy

Received: 31 August 2010
Accepted: 20 June 2011

Abstract

Aims. We investigate the distribution of the luminous and the dark matter components in the isolated ellipticals NGC 7052 and NGC 7785, which are embedded in an emitting hot gas halo, by means of relevant X-ray and photometric data.

Methods. To calculate the dark matter distribution in these rare objects, we performed an improved X-ray analysis of the XMM-Newton data of NGC 7785, and we used former results based on Chandra data of NGC 7052. For each object we also derived the stellar spheroid length scale from the surface photometry and the spheroid stellar mass from an analysis of the galaxy spectral energy distribution.

Results. We find that a dark matter component is present in these objects. It is subdominant and mixed with the luminous matter inside the optical region half-light radius wide, while it dominates the gravitational potential at outer radii. On the whole, the dark halo structure is very similar to that found around spirals of comparable luminosity and it is well reproduced by a Burkert halo, while a Sérsic spheroid accounts well for the baryonic component.