On the dark matter haloes inner structure and galaxy morphology

TL;DR

This paper investigates how galaxy morphology influences the inner density profile of dark matter haloes, revealing a monotonic flattening with increasing rotation velocity and a steepening at low velocities, aligning qualitatively with simulations.

Contribution

It extends previous models to include galaxy morphology effects on halo inner slopes, providing new insights into the relation between halo structure and galaxy type across different mass ranges.

Findings

Inner slope $\alpha$ flattens from -1 to 0 with increasing rotation velocity.

Steepening of $\alpha$ occurs in low-mass, non-rotationally supported galaxies.

Results are qualitatively consistent with SPH simulations but suggest flatter slopes at very low masses.

Abstract

In the present paper, we extend the study of Del Popolo (2010) to determine the slope of the inner density profile of galaxy haloes with different morphologies. We study how galaxy morphology changes the relation between the inner slope of the galaxy halo density profile, $\alpha$, and the stellar mass, $M_{*}$, or rotation velocity $V_{\rm rot}$. For this, we use the model of Del Popolo (2009) in combination with observed data from the Romanowsky \& Fall (2012) sample of elliptical and spiral galaxies, the Local Group sample compiled by McConnachie (2012), and the simulation results by Cloet-Osselaer et al. (2014). We find that the slope $\alpha$ flattens monotonically, from $\alpha \simeq -1 $ at $V_{\rm rot} \simeq 250$ km/s, to $\alpha \simeq 0 $. After $V_{\rm rot}\simeq 25$ km/s the slope starts to steepen. The steepening happens in the mass range dominated by non-rotationally supported galaxies (e.g., dSphs) and depends on the level of offset in the angular momentum of rotationally and non-rotationally dominated galaxies. The steepening is a consequence of the decrease in baryons content, and angular momentum in spheroidal dwarf galaxies. We finally compare our result to the SPH simulations of Di Cintio. Our result is in qualitatively agreement with their simulations, with the main difference that the inner slope $\alpha$ at small stellar masses ($M_* \lesssim10^{8} M_{\odot}$) is flatter than that in their simulations. As a result, the claim that finding a core in dwarf galaxies with masses slightly smaller than $\simeq 10^6 M_{\odot}$, (as in the Di Cintio, or Governato, supernovae feedback mechanism) would be a problem for the $\Lambda$CDM model must be probably revised.