Globular Clusters and Dark Satellite Galaxies Through the Stream Velocity

Abstract

The formation of purely baryonic globular clusters with no gravitationally bound dark matter is still a theoretical challenge. We show that these objects might form naturally whenever there is a relative stream velocity between baryons and dark matter. The stream velocity causes a phase shift between linear modes of baryonic and dark matter perturbations, which translates to a spatial offset between the two components when they collapse. For a 2σ (3σ) density fluctuation, baryonic clumps with masses in the range 105−2.5×106 M⊙ (105−4×106 M⊙) collapse outside the virial radii of their counterpart dark matter halos. These objects could survive as long-lived dark matter-free objects and might conceivably become globular clusters. In addition, their dark matter counterparts, which were deprived of gas, might become dark satellite galaxies.