Model comparison of the dark matter profiles of Fornax, Sculptor, Carina and Sextans

TL;DR

This study uses orbit-based dynamical models and Bayesian evidence to compare dark matter profiles in four dwarf spheroidal galaxies, finding no single profile fits all, but consistent mass distributions suggest strong constraints for cosmological models.

Contribution

It provides a comparative analysis of dark matter profiles in multiple dwarf galaxies using Bayesian methods, highlighting the diversity and constraints on dark matter models.

Findings

No preference for specific parametric profiles per galaxy.

Combined evidence disfavors identical cored profiles for all galaxies.

Consistent mass distribution across galaxies from r_{-3} to outer data points.

Abstract

We use orbit based dynamical models to fit the 2nd and 4th moments of the line of sight velocity distributions of the Fornax, Sculptor, Carina and Sextans dwarf spheroidal galaxies. Our goal is to compare dark matter profile models of these four systems using Bayesian evidence. We consider NFW, Einasto and several cored profiles for their dark halos and present the probability distribution functions of the model parameters. When considering each system separately, we find there is no preference for one of these specific parametric density profiles. However, the combined evidence shows that it is unlikely that all galaxies are embedded in the same type of cored profiles of the form \rho_{DM} \propto 1/(1 + r^2)^{\beta/2}, where \beta = 3, 4. For each galaxy, we also obtain an almost model independent, and therefore accurate, measurement of the logarithmic slope of the dark matter density distribution at a radius ~ r_{-3}, i.e. where the logarithmic slope of the stellar density profile is -3. This slope ranges from ~ -1.4 for Fornax to ~ -1.1 for Sextans, both at ~ 1 kpc. All our best fit models essentially have the same mass distribution over a large range in radius (from just below r_{-3} to the last measured data point). This remarkable finding likely implies much stronger constraints on the characteristics that subhalos extracted from cosmological simulations should have in order to host the dSph galaxies around the Milky Way.