Modelling mass distribution in elliptical galaxies: mass profiles and their correlation with velocity dispersion profiles

TL;DR

This study develops detailed mass models for nearly spherical elliptical galaxies, revealing a strong correlation between mass density and velocity dispersion profiles, and emphasizing the importance of dark matter in shaping these profiles.

Contribution

It introduces a comprehensive set of two-component mass models that accurately reproduce observed velocity dispersion profiles and uncover a tight correlation between mass density and velocity dispersion slopes.

Findings

Two-component models match observed VP slopes within R_eff.

A tight correlation exists between mass density slope and velocity dispersion slope.

Total mass profiles likely have a curvature pattern influenced by dark matter.

Abstract

We assemble a statistical set of global mass models for ~2,000 nearly spherical SDSS galaxies at a mean redshift of 0.12 based on their aperture velocity dispersions and newly derived luminosity profiles in conjunction with published velocity dispersion profiles and empirical properties and relations of galaxy and halo parameters. When two-component (i.e. stellar plus dark) mass models are fitted to the SDSS aperture velocity dispersions, the predicted velocity dispersion profile (VP) slopes within the effective radius R_eff match well the distribution in observed elliptical galaxies. In contrast, the single-component models cannot reproduce the VP slope distribution. From a number of input variations the models exhibit for the radial range 0.1 R_eff < r < R_eff a tight correlation <gamma_e>=(1.865+/-0.008)+(-4.93+/-0.15)<eta> where <gamma_e> is the mean slope absolute value of the total mass density and <eta> is the mean slope of the velocity dispersion profile, which leads to a super-isothermal <gamma_e> = 2.15+/-0.04 for <eta>=-0.058+/-0.008 in observed elliptical galaxies. Furthermore, the successful two-component models appear to imply a typical slope curvature pattern in the total mass profile because for the observed steep luminosity (stellar mass) profile and the weak lensing inferred halo profile at large radii a total mass profile with monotonically varying slope would require too high DM density in the optical region giving rise to too large aperture velocity dispersion and too shallow VP.