The baryonic mass-velocity relation: clues to feedback processes during structure formation and the cosmic baryon inventory

We show that a global relation between baryonic mass and virial velocity can be constructed from the scale of dwarf galaxies up to that of rich galaxy clusters. The slope of this relation is close to that expected if dark matter haloes form in the standard hierarchical cosmogony and capture a universal baryon fraction, once the details of halo structure and the adiabatic contraction of haloes due to cooling gas are taken into account. The scatter and deficiency of baryons within low- mass haloes (V-vir < 50 km s(-1)) are consistent with the expected suppression of gas accretion by photoevaporation due to the cosmic UV background at high redshift. The data are not consistent with significant gas removal from strong supernovae winds unless the velocities of galaxies measured from their gas kinematics are significantly lower than the true halo velocities for objects with V-vir < 100 km s(-1). Thus models such as cold dark matter (LambdaCDM) with a steep mass function of haloes may find it difficult to reproduce the baryonic mass-velocity relation presented here whilst at the same time reproducing the flat luminosity HI function of galaxies. Galaxies hold about 10 per cent of the baryons in the Universe, which is close to the collapsed mass fraction expected within hierarchical models on these scales, suggesting a high efficiency for galaxy formation. Most of the baryons are expected to be evenly distributed between diffuse intergalactic gas in low-density environments and the intragalactic medium within galaxy groups.