Simulating Observations of Dark Matter Dominated Galaxies: Towards the Optimal Halo Profile

Abstract

Low Surface Brightness (LSB) galaxies are dominated by dark matter, and their rotationcurves thus reflect their dark matter distribution. Recent high-resolution rotationcurves suggest that their dark matter mass-density distributions are dominated bya constant-density core. This seems inconsistent with the predictions of Cold DarkMatter (CDM) models which produce halos with compact density cusps and steepmass-density profiles. However, the observationally determined mass profiles may beaffected by non-circular motions, asymmetries and offsets between optical and dynamicalcentres, all of which tend to lower the observed slopes. Here we determine theimpact of each of these effects on a variety of halo models, and compare the resultswith observed mass-density profiles. Our simulations suggest that no single systematiceffect can reconcile the data with the cuspy CDM halos. The data are best describedby a model with a soft core with an inner power-law mass-density slope = −0.2±0.2.However, no single universal halo profile provides a completely adequate descriptionof the data.