Low-mass Globular Clusters from Stripped Dark Matter Halos

Abstract

Abstract The origin and formation of globular clusters (GCs) has remained a mystery. We present a formation scenario for ancient GC-like objects that form in ultrahigh-resolution simulations (smallest cell size < 0.1 pc, mass resolution M cell = 4 M ⊙). The simulations are cosmological zoom-in simulations of dwarf galaxies within the stellar mass range 106−7 M ⊙ that match Local Group dwarf properties well. Our investigation reveals GCs hosting ancient stellar populations, characterized by a lack of dark matter (DM) in the present epoch. The clusters exhibit short, episodic star formation histories, occasionally marked by the presence of multiple stellar generations. The metallicity distributions show a widening, encompassing stars in the range of 10−4 < Z ⋆/Z ⊙ < 1. The presence of these objects is attributable to star formation occurring within low-mass DM halos (M halo ≈ 106 M ⊙) during the early stages of the Universe, preceding reionization (z ≳ 7). As these clusters are accreted into dwarf galaxies, DM is preferentially subjected to tidal stripping, with an average accretion redshift of z ¯ ≈ 5 .