How Concentrated Are The Haloes Of Low Surface Brightness Galaxies In The Cold Dark Matter Model?

Abstract

We investigate whether a correlation exists between the concentration and spin parameters of dark matter haloes forming in LCDM N-body simulations. In particular, we focus on haloes with virial masses characteristic of the hosts of Low Surface Brightness (LSB) and High Surface Brightness (HSB) galaxies. Our analysis demonstrates that concentration and spin are anti-correlated. If we assume that a galaxy disk forms in one of these haloes from baryons that approximately conserved angular momentum during their dissipation into the rotationally supported disk, then it is possible to estimate the disk's central surface density. For an appropriate choice of mass-to-light ratio, we can place constraints on the central surface brightness of the disk and hence identify the analogues of the host haloes of LSB and HSB galaxies. We find that our LSB galaxy analogues occupy haloes that have lower concentrations than might be expected based on consideration of the mass-concentration relation for the LCDM cosmology. The distribution of concentrations peaks at c~6, in good agreement with observational data, although there are important differences between the shapes of the simulated and observationally inferred distributions. This suggests that LSB galaxies inhabit a biased subsample of the halo population, and that this bias may be an important ingredient for resolving the current debate regarding the structure of LSB galaxy dark matter haloes.