Globular Cluster Populations: Results Including S$^4$G Late-Type Galaxies

TL;DR

This study analyzes globular cluster populations in 73 late-type galaxies from the S$^4$G survey, revealing a mass-dependent relationship and differences from early-type galaxies, with implications for galaxy evolution and cluster distribution.

Contribution

It provides the first detailed comparison of globular cluster richness in late-type galaxies with early types, establishing a mass-dependent relation for T$_{ m N}$ and its implications.

Findings

Globular cluster richness correlates with galaxy stellar mass.

Late-type galaxies do not split into two T$_{ m N}$ families at low mass.

Clusters are most common around galaxies with M$_* \, \sim 10^{10.8}$ M$_\odot$.

Abstract

Using 3.6 and 4.5$\mu$m images of 73 late-type, edge-on galaxies from the S$^4$G survey, we compare the richness of the globular cluster populations of these galaxies to those of early type galaxies that we measured previously. In general, the galaxies presented here fill in the distribution for galaxies with lower stellar mass, M$_*$, specifically $\log({\rm M}_*/{\rm M}_\odot) < 10$, overlap the results for early-type galaxies of similar masses, and, by doing so, strengthen the case for a dependence of the number of globular clusters per $10^9\ {\rm M}_\odot$ of galaxy stellar mass, T$_{\rm N}$, on M$_*$. For $8.5 < \log ({\rm M}_*/{\rm M}_\odot) < 10.5$ we find the relationship can be satisfactorily described as T$_{\rm N} = ({\rm M}_*/10^{6.7})^{-0.56}$ when M$_*$ is expressed in solar masses. The functional form of the relationship is only weakly constrained and extrapolation outside this range is not advised. Our late-type galaxies, in contrast to our early-types, do not show the tendency for low mass galaxies to split into two T$_{\rm N}$ families. Using these results and a galaxy stellar mass function from the literature, we calculate that in a volume limited, local Universe sample, clusters are most likely to be found around fairly massive galaxies (M$_* \sim 10^{10.8}$ M$_\odot$) and present a fitting function for the volume number density of clusters as a function of parent galaxy stellar mass. We find no correlation between T$_{\rm N}$ and large-scale environment, but do find a tendency for galaxies of fixed M$_*$ to have larger T$_{\rm N}$ if they have converted a larger proportion of their baryons into stars.