Globular Clusters and Dark Satellite Galaxies through the Stream Velocity

TL;DR

This paper proposes that stream velocities between baryons and dark matter can naturally lead to the formation of baryonic globular clusters without dark matter, and also produce dark satellite galaxies, explaining their origins.

Contribution

It introduces a mechanism where stream velocities cause spatial offsets in collapse, leading to dark matter-free globular clusters and dark satellite galaxies, a novel formation scenario.

Findings

Baryonic clumps form outside dark matter halos due to stream velocities.

These baryonic objects can survive as long-lived globular clusters.

Dark matter counterparts may become dark satellite galaxies.

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 2sigma (3sigma) density fluctuation, baryonic clumps with masses in the range 1e5 - 2.5e6 Msun (1e5 - 4e6 Msun) 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.