Low-mass globular clusters from stripped dark matter halos

TL;DR

This paper proposes a formation scenario for ancient globular cluster-like objects originating in early low-mass dark matter halos, formed before Reionization, and now observed as dark matter-free clusters within dwarf galaxies, based on high-resolution cosmological simulations.

Contribution

It introduces a new formation pathway for globular clusters in ultra-high resolution simulations, showing their origin in early low-mass dark matter halos and subsequent tidal stripping.

Findings

Globular clusters host ancient stellar populations with no dark matter.

Clusters show episodic star formation and multiple stellar generations.

Metallicity spans a wide range from $10^{-4}$ to 1 Z$_\odot$.

Abstract

The origin and formation of globular clusters has remained a mystery. We present a formation scenario for ancient globular cluster-like objects that form in ultra-high resolution simulations (smallest cell size $<0.1\,\mathrm{pc}$, mass resolution $M_\mathrm{cell}=4\,\mathrm{M}_\odot$). The simulations are cosmological zoom-in simulations of dwarf galaxies within the stellar mass range $10^{6-7}\,\mathrm{M}_\odot$ that match Local Group dwarf properties well. Our investigation reveals globular clusters hosting ancient stellar populations, characterized by a lack of dark matter 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 $10^{-4} < Z_\star/\mathrm{Z}_\odot < 1$. The presence of these objects is attributable to star formation occurring within low-mass dark matter halos ($M_\mathrm{halo}\approx10^6\,\mathrm{M}_\odot$) during the early stages of the Universe, preceding Reionization ($z\gtrsim7$). As these clusters are accreted into dwarf galaxies, dark matter is preferentially subjected to tidal stripping, with an average accretion redshift of $\bar{z} \approx 5$.