Improved Modeling of the Mass Distribution of Disk Galaxies by the Einasto Halo Model

TL;DR

This study demonstrates that the Einasto halo model provides a significantly better fit to galaxy rotation curves than traditional models, revealing new insights into dark matter halo structures and challenging some LCDM simulation predictions.

Contribution

The paper introduces the Einasto halo model as a superior fit for galaxy rotation curves and explores its implications for dark matter halo profiles and cosmological theories.

Findings

Einasto model fits rotation curves better than NFW or Iso models.

The Einasto index correlates with halo mass, differing from LCDM predictions.

Outer halo density declines more steeply than NFW or Iso models.

Abstract

(Abridged) The analysis of the rotation curves (RCs) of spiral galaxies provides an efficient diagnostic for studying the properties of dark matter halos and their relations with the baryonic material. We have modeled the RCs of galaxies from The HI Nearby Galaxy Survey (THINGS) with the Einasto halo model, which has emerged as the best-fitting model of the halos arising in dissipationless cosmological N-body simulations. We find that the RCs are significantly better fit with the Einasto halo than with either a pseudo-isothermal sphere (Iso) or Navarro-Frenk-White (NFW) halo models. In our best-fit models, the radius of density slope -2 and the density at this radius are highly correlated. The Einasto index, which controls the overall shape of the density profile, is near unity on average for intermediate and low mass halos. This is not in agreement with the predictions from LCDM simulations. The indices of the most massive halos are in rough agreement with those of cosmological simulations and appear correlated with the halo virial mass. We find that a typical Einasto density profile declines more strongly in its outermost parts than any of the Iso or NFW models whereas it is relatively shallow in its innermost regions. The core nature of those regions of halos thus extends the cusp-core controversy found for the NFW model with low surface density galaxies to the Einasto halo with more massive galaxies like those of THINGS. We thus find that the Einasto halo model provides, so far, the best match to the observed RCs, and can therefore be considered as a new standard model for dark matter halos.