High-resolution dark matter density profiles of THINGS dwarf galaxies: Correcting for non-circular motions

TL;DR

This paper introduces a new method to extract circular velocity components from HI data to better constrain dark matter profiles in dwarf galaxies, addressing the cusp/core problem by reducing non-circular motion effects.

Contribution

The authors develop a novel technique to remove non-circular motions from HI velocity fields, enabling more accurate dark matter profile measurements in dwarf galaxies.

Findings

Dark matter in IC 2574 and NGC 2366 favors core-like profiles over cuspy NFW profiles.

The new method significantly reduces non-circular motion effects in rotation curves.

Results are robust against variations in stellar mass-to-light ratio assumptions.

Abstract

We present a new method to remove the impact of random and small-scale non-circular motions from HI velocity fields in galaxies in order to better constrain the dark matter properties for these objects. This method extracts the circularly rotating velocity components from the HI data cube and condenses them into a so-called bulk velocity field. We derive high-resolution rotation curves of IC 2574 and NGC 2366 based on bulk velocity fields derived from The HI Nearby Galaxy Survey (THINGS) obtained at the VLA. The bulk velocity field rotation curves are significantly less affected by non-circular motions and constrain the dark matter distribution in our galaxies, allowing us to address the discrepancy between the inferred and predicted dark matter distribution in galaxies (the "cusp/core" problem). Spitzer Infrared Nearby Galaxies Survey (SINGS) 3.6 micron data as well as ancillary optical information, are used to separate the baryons from the total matter content. Using stellar population synthesis models, assuming various sets of metallicity and star formation histories, we compute stellar mass-to-light ratios for the 3.6 and 4.5 micron bands. Using our predicted value for the 3.6 micron stellar mass-to-light ratio, we find that the observed dark matter distributions of IC 2574 and NGC 2366 are inconsistent with the cuspy dark matter halo predicted by LCDM models, even after corrections for non-circular motions. This result also holds for other assumptions about the stellar mass-to-light ratio. The distribution of dark matter within our sample galaxies is best described by models with a kpc-sized constant-density core.