41 6 v 2 1 S ep 2 00 3 The origin of cores and density profiles of gaseous baryonic structures

We study the origin of cores and density profiles of gaseous baryonic structures in cosmology. By treating the baryons as a viscous gas, we find that both spheres and disks are possible solutions. We find analytically that the density profiles have inner and outer solutions, which in general are different. For disks we identify a central core, with density profile ρd = constant, and the outer profile ρd ∼ r . For spherical structures we find the profile ρs ∼ r . In the presence of a dominating central black hole we find the inner profile ρ ∼ r. When the mass is dominated by a dark matter component then the baryonic density profile will depend on the dark matter profile, and we point out how one can use this connection to infer the DM profile directly by observing the baryonic density profile. Subject headings: galaxies: clusters: general — galaxies: structure — methods: analytical