Formation of globular cluster systems: from dwarf galaxies to giants

Abstract

Globular cluster (GC) systems around galaxies of a vast mass range show remarkably simple scaling relations. The combined mass of all GCs is a constant fraction of the total galaxy mass and the mean metallicity and metallicity dispersion of the GC system scale up weakly with galaxy mass. The metallicity of massive, metal-poor ("blue") clusters increases with cluster mass, while that of metal-rich ("red") clusters does not. A significant age-metallicity relation emerges from analysis of resolved stellar populations in Galactic GCs and unresolved populations in nearby galaxies. Remarkably, all these trends can be explained by a simple merger-based model developed in previous work and updated here using recent observations of galaxy scaling relations at high redshift.We show that the increasing dispersion of GC metallicity distributions with galaxy mass is a robust prediction of the model. It arises from more massive galaxies having more mergers that combine satellite GC systems. The average metallicity also increases by 0.6 dex over 3 dex in halo mass. The models show a non-linear trend between the GC system mass and host galaxy mass which is consistent with the data. The model does not consider GC self-enrichment, yet predicts a correlation between cluster mass and metallicity for massive blue clusters. The age-metallicity relation is another robust prediction of the model. Half of all clusters are predicted to form within the redshift range 5 < z < 2.3, corresponding to ages of 10.8 − 12.5 Gyr, in halos of masses 10 11 − 10 12.5 M .

Modeling Dense Star Clusters in the Milky Way and Beyond with the CMC Cluster Catalog

“…Clusters with smaller r v are denser (see Section 3), and therefore feature a higher rate of interactions that form BBHs. This is consistent with the results shown in a number of previous analyses (e.g., Rodriguez et al 2016;Zevin et al 2018;Choksi et al 2018). It is clear from Section 3 that an initial r v of 0.5 pc is appropriate for a fraction of observed clusters in the MW (specifically, those that are most centrally concentrated at present).…”

The Fornax 3D project: Non-linear colour–metallicity relation of globular clusters

“…Ashman & Zepf 1992;Forbes et al 1997;Côté et al 1998;Beasley et al 2002;Lee & Jang 2016;Beasley et al 2018) and is also expected in the hierarchical merger scheme of galaxy formation (e.g. Muratov & Gnedin 2010;Tonini 2013;Li & Gnedin 2014;Choksi et al 2018;Kruijssen et al 2019). It is assumed that the red, metal-rich GCs either form in-situ in massive halos around the peak of star formation or during major mergers of gas-rich galaxies together with the bulk of in-situ stars.…”

On the Use of Field RR Lyrae as Galactic Probes. I. The Oosterhoff Dichotomy Based on Fundamental Variables*

“…Moreover, the metal-poor tail does not approach the limit of field Halo stars, while the metal-rich tail does not approach the limit of old metalrich Bulge stars. The difference is well known and it is tightly connected with the formation mechanism of globular clusters (Choksi et al 2018).…”