Clearing the hurdle: The mass of globular cluster systems as a function of host galaxy mass

Abstract

Current observational evidence suggests that all large galaxies contain globular clusters (GCs), while the smallest galaxies do not. Over what galaxy mass range does the transition from GCs to no GCs occur? We investigate this question using galaxies in the Local Group, nearby dwarf galaxies, and galaxies in the Virgo Cluster Survey. We consider four types of statistical models: (1) logistic regression to model the probability that a galaxy of stellar mass M * has any number of GCs; (2) Poisson regression to model the number of GCs versus M * , (3) linear regression to model the relation between GC system mass (log M gcs ) and host galaxy mass (log M ), and (4) a Bayesian lognormal hurdle model of the GC system mass as a function of galaxy stellar mass for the entire data sample. From the logistic regression, we find that the 50% probability point for a galaxy to contain GCs is M * = 10 6.8 M . From post-fit diagnostics, we find that Poisson regression is an inappropriate description of the data. Ultimately, we find that the Bayesian lognormal hurdle model, which is able to describe how the mass of the GC system varies with M * even in the presence of many galaxies with no GCs, is the most appropriate model over the range of our data. In an Appendix, we also present photometry for the little-known GC in the Local Group dwarf Ursa Major II.

Introducing EMP-Pathfinder: modelling the simultaneous formation and evolution of stellar clusters in their host galaxies

“…This corresponds to galaxies resolved by 100 stellar particles in our simulations, and it roughly corresponds to the lowest mass galaxies observed to host GCs (see e.g. Forbes et al 2018b;Eadie et al 2021). Additionally, the lowest gravitationally-resolved gas scale in the gas at 𝑧 ∼ 2 is ∼ 27 proper pc.…”

Formation of proto-globular cluster candidates in cosmological simulations of dwarf galaxies at $z>4$

“…The fraction of stars contained in GCs in low-mass (𝑀 ★ 10 7 M ) galaxies is 1 − 10% (Georgiev et al 2010;Hudson et al 2014;Larsen 2017), which is much higher than in more massive systems and indicates that cluster-related star formation plays an important role in the growth of these systems; this is especially true at early times, as the clusters can contain ∼25% of the metal-poor ([Fe/H] < −2) stars in dwarf galaxies (Larsen et al 2014). However, the fraction of galaxies hosting at least one GC drops off strongly towards low stellar masses (Georgiev et al 2010;Burkert & Forbes 2020;Eadie et al 2021), meaning that conditions for GC formation are met in only a subset of dwarf galaxies; an understanding of which dwarf galaxy progenitors achieve the necessary conditions for GC formation may prove essential for understanding GC formation more broadly.…”

Introducing EMP-Pathfinder: modelling the simultaneous formation and evolution of stellar clusters in their host galaxies

“…This corresponds to galaxies resolved by 100 stellar particles in our simulations, and it roughly corresponds to the lowest mass galaxies observed to host GCs (see e.g. Forbes et al 2018b;Eadie et al 2021). We thus have the baryonic mass resolution required to resolve the galactic environments where massive cluster formation is expected to occur at high-redshift.…”