Simulating observations of dark matter dominated galaxies: towards the optimal halo profile

Low surface brightness galaxies are dominated by dark matter, and their rotation curves thus reflect their dark matter distribution. Recent high-resolution rotation curves suggest that their dark matter mass-density distributions are dominated by a constant-density core. This seems inconsistent with the predictions of cold dark matter (CDM) models which produce haloes with compact density cusps and steep mass-density profiles. However, the observationally determined mass profiles may be affected by non-circular motions, asymmetries and offsets between optical and dynamical centres, all of which tend to lower the observed slopes. Here we determine the impact of each of these effects on a variety of halo models, and we compare the results with observed mass-density profiles. Our simulations suggest that no single systematic effect can reconcile the data with the cuspy CDM haloes. The data are best described by a model with a soft core with an inner power-law mass-density slope alpha = -0.2+/-0.2. However, no single universal halo profile provides a completely adequate description of the data.