Navarro-Frenk-White dark matter profile and the dark halos around disk systems

TL;DR

This study analyzes over 3200 galaxy rotation curves to test the Navarro-Frenk-White dark matter profile, finding it generally inadequate to explain observed galaxy kinematics and challenging the predictions of the $\\Lambda$CDM model.

Contribution

It provides a comprehensive empirical assessment of NFW profile fits across diverse disk galaxies, highlighting significant discrepancies with theoretical expectations.

Findings

NFW profile fits are generally poor for the galaxy sample.

Best-fit parameters contradict $\\Lambda$CDM expectations.

Model fails to reproduce observed scaling relations.

Abstract

The $\Lambda$ cold dark matter ($\Lambda$CDM) scenario well describes the Universe at large scales, but shows some serious difficulties at small scales: the inner dark matter (DM) density profiles of spiral galaxies generally appear to be cored, without the $r^{-1}$ predicted by N-body simulations in the above scenario. In a more physical context, the baryons in the galaxy might backreact and erase the original cusp through supernova explosions. Before that this effect be investigated, it is important to determine how wide and frequent the discrepancy between observed and N-body predicted profiles is and what its features are. We used more than 3200 quite extended rotation curves (RCs) of good quality and high resolution of disk systems. The curves cover all magnitude ranges. These RCs were condensed into 26 coadded RCs, each of them built with individual RCs of galaxies of similar luminosity and morphology. We performed mass models of these 26 RCs using the Navarro-Frenk-White (NFW) profile for the contribution of the DM halo to the circular velocity and the exponential Freeman disk for that of the stellar disk. The fits are generally poor in all the 26 cases: in several cases, we find $\chi^2_{red}>2$. Moreover, the best-fitting values of three parameters of the model ($c$, $M_D$, and $M_{vir}$) combined with those of their 1$\sigma$ uncertainty clearly contradict well-known expectations of the $\Lambda$CDM scenario. We also tested the scaling relations that exist in spirals with the fitting outcome: the modeling does not account for these scaling relations. Therefore, NFW halo density law cannot account for the kinematics of the whole family of disk galaxies. It is therefore mandatory for the $\Lambda CDM$ scenario in any disk galaxy of any luminosity to transform initial cusps into the observed cores.