Revisiting the relation between the number of globular clusters and galaxy mass for low mass galaxies

TL;DR

This study revisits the relationship between the number of globular clusters and galaxy mass in low-mass galaxies, finding a nearly linear relation that challenges existing formation models and suggests a possible variation in mean GC mass.

Contribution

It introduces a new method for estimating galaxy mass and extends the N_GC-M_T relation to lower mass galaxies, providing insights into globular cluster formation and galaxy evolution.

Findings

The N_GC-M_T relation is nearly linear down to M_T ~ 10^{8.75} M_sun.

The relation extends to galaxies with less than one GC on average.

The results challenge models where GCs form in central high-density regions and are scattered outward.

Abstract

Using a new method to estimate total galaxy mass (M$_{\rm T}$) and two samples of low luminosity galaxies containing measurements of the number of globular clusters (GCs) per galaxy (N$_{\rm GC}$), we revisit the N$_{\rm GC}-$M$_{\rm T}$ relation using a total of 203 galaxies, 157 of which have M$_{\rm T}$ $\ \le 10^{10}$ M$_\odot$. We find that the relation is nearly linear, N$_{\rm GC} \propto$ M$_{\rm T}^{0.92\pm0.08}$ down to at least M$_{\rm T} \sim 10^{8.75}$ M$_\odot$. Because the relationship extends to galaxies that average less than one GC per galaxy and to a mass range in which mergers are relatively rare, the relationship cannot be solely an emergent property of hierarchical galaxy formation. The character of the radial GC distribution in low mass galaxies, and the lack of mergers at these galaxy masses, also appears to challenge models in which the GCs form in central, dissipatively concentrated high-density, high-pressure regions and are then scattered to large radius. The slight difference between the fitted power-law exponent and a value of one, leaves room for a shallow M$_{\rm T}$-dependent variation in the mean mass per GC that would allow the relation between total mass in GCs and M$_{\rm T}$ to be linear.