Density profile slope in Dwarfs and environment

TL;DR

This paper investigates how environmental factors and baryon fractions influence the dark matter density profiles of dwarf galaxies, revealing correlations between tidal torquing, baryon content, and profile steepness, with applications to observed galaxy rotation curves.

Contribution

It introduces a model linking tidal torquing and baryon fraction to the shape of dwarf galaxy density profiles, validated through analysis of specific galaxy rotation curves.

Findings

Dwarfs with less tidal torquing have steeper profiles.

Lower baryon fractions correlate with steeper density profiles.

Profiles can be approximated by Burkert or Einasto models depending on conditions.

Abstract

In the present paper, we study how the dark matter density profiles of dwarfs galaxies in the mass range $10^8-10^{10} M_{\odot}$ are modified by the interaction of the dwarf in study with the neighboring structures, and by changing baryon fraction in dwarfs. As already shown in Del Popolo (2009), the slope of density profile of inner halos flattens with decreasing halo mass and the profile is well approximated by a Burkert's profile. The analysis shows that dwarfs who suffered a smaller tidal torquing (consequently having smaller angular momentum) are characterized by steeper profiles with respect to dwarfs subject to higher torque, and similarly dwarfs having a smaller baryons fraction have also steeper profiles than those having a larger baryon fraction. In the case tidal torquing is shut down and baryons are not present, the density profile is very well approximated by an Einasto profile, similarly to dwarfs obtained in dissipationless N-body simulations. We then apply the result of the previous analysis to the dark matter halo rotation curves of three different dwarfs, namely NGC 2976, known to have a flat inner core, NGC 5949 having a profile intermediate between a cored and a cuspy one, and NGC 5963 having a cuspy profile. After calculating baryon fraction, which is $\simeq 0.1$ for the three galaxies, we fitted the rotation curves changing the value of angular momentum. NGC 2976, has an higher value of ordered angular momentum ($\lambda \simeq 0.04$) with respect to NGC 5949 ($\lambda \simeq 0.025$) and in the case of NGC 5963 the very steep profile can be obtained with a low value of $\lambda$ ($\lambda \simeq 0.02$) and also decreasing the value of the random angular momentum. In the case of NGC 2976 tidal interaction with M81 could have also influenced the inner part of the density profile.