Dark matter halos around isolated ellipticals

TL;DR

This study analyzes the distribution of dark and luminous matter in isolated elliptical galaxies NGC 7052 and NGC 7785 using X-ray and photometric data, revealing dark matter presence and halo structure similar to spiral galaxies.

Contribution

It provides detailed dark matter distribution analysis in isolated ellipticals, employing improved X-ray data and photometric analysis, and compares the halo structure to spiral galaxies.

Findings

Dark matter is present and subdominant inside the optical region.

Dark matter dominates at outer radii.

Dark halo structure resembles that of spiral galaxies.

Abstract

We investigate the distribution of the luminous and the dark matter components in the isolated ellipticals NGC 7052 and NGC 7785, embedded in an emitting hot gas halo, by means of relevant X-ray and photometric data. In order 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. 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 Sersic spheroid accounts well for the baryonic component.