We use the rotation curves (RC) of a sample of dark matter dominated dwarf and low-surface brightness (LSB) late-type galaxies to study their radial mass distributions. We find that the shape of the RCs is remarkably similar for all (both dwarf and LSB) galaxies in the sample, suggesting a self-similar density distribution of their dark matter (DM) halos. This shape can be reproduced well by a density profile with a shallow central cusp [\rho(r) propto 1/rgamma,gamma ~ 0.2-0.4], corresponding to a steeply rising velocity curve [v(r) propto r^g,g ~ 0.9-0.8]. We also find that the observed shape is well matched by the density profiles of dark matter halos formed in very high resolution simulations of the standard cold dark matter model (CDM), the low-density CDM model with cosmological constant (LambdaCDM), and the cold+hot dark matter model with two types of neutrino (CHDM). Finally, we find that the dark matter halos in our hierarchical simulations and the real galaxies in our sample exhibit a similar decrease in their characteristic densities with increasing characteristic radial scales, and increase in their maximum rotation velocities with increasing radii at which their maximum velocity occurs.
Large Scale Structure: Tracks and Traces
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