Globular Clusters Formed within Dark Halos I: present-day abundance, distribution and kinematics

TL;DR

This paper investigates the formation of metal-poor globular clusters within dark matter halos in the early universe, predicting their present-day distribution, abundance, and kinematics using simulations and models, and compares these with observations.

Contribution

It introduces a model where GCs form in dark matter halos before reionization, predicting their properties and comparing with observational data.

Findings

GCs are predicted to be highly clustered around galaxies

The number of GCs scales with halo mass as observed

Most GCs are embedded in extended dark matter halos

Abstract

We explore a scenario where metal poor globular clusters (GCs) form at the centres of their own dark matter halos in the early universe before reionization. This hypothesis leads to predictions about the abundance, distribution and kinematics of GCs today that we explore using cosmological N-body simulations and analytical modelling. We find that selecting the massive tail of collapsed objects at $z\gtrsim 9$ as GC formation sites leads to four main predictions: i) a highly clustered population of GCs around galaxies today, ii) a natural scaling between number of GCs and halo virial mass that follows roughly the observed trend, iii) a very low number of free floating GCs outside massive halos and iv) GCs should be embedded within massive and extended dark matter (sub)halos. We find that the strongest constraint to the model is given by the combination of (i) and (ii): a mass cut to tagged GCs halos which accounts for the number density of metal poor GCs today predicts a radial distribution that is too extended compared to recent observations. On the other hand, a mass cut sufficient to match the observed half number radius could only explain 60% of the metal poor population. In all cases, observations favour early redshifts for GC formation ($z\geq 15$).