A Catalog of Globular Cluster Systems: What Determines the Size of a Galaxy's Globular Cluster Population?

TL;DR

This paper compiles a catalog of 422 galaxies to analyze factors influencing globular cluster populations, revealing correlations with galaxy mass, size, and halo properties, and proposing empirical predictors for GC numbers.

Contribution

It provides a comprehensive catalog and identifies new empirical relations and correlations, especially linking GC populations to galaxy halo mass and structural parameters.

Findings

N_GC correlates nonlinearly with galaxy bulge dynamical mass.

GC specific frequency exhibits a U-shape trend with galaxy luminosity.

Total GC population can be predicted by (R_e σ_e)^1.3, aligning with Fundamental Plane relations.

Abstract

We present a catalog of 422 galaxies with published measurements of their globular cluster (GC) populations. Of these, 248 are E galaxies, 93 are S0 galaxies, and 81 are spirals or irregulars. Among various correlations of the total number of GCs with other global galaxy properties, we find that N_GC correlates well though nonlinearly with the dynamical mass of the galaxy bulge M_dyn = 4 \sigma_e^2 R_e /G, where \sigma_e is the central velocity dispersion and R_e the effective radius of the galaxy light profile. We also present updated versions of the GC specific frequency S_N and specific mass S_M versus host galaxy luminosity and baryonic mass. These graphs exhibit the previously known U-shape: highest S_N or S_M values occur for either dwarfs or supergiants, but in the midrange of galaxy size (10^9 - 10^10 L_Sun) the GC numbers fall along a well defined baseline value of S_N ~ 1 or S_M ~ 0.1, similar among all galaxy types. Along with other recent discussions, we suggest that this trend may represent the effects of feedback, which systematically inhibited early star formation at either very low or very high galaxy mass, but which had its minimum effect for intermediate masses. Our results strongly reinforce recent proposals that GC formation efficiency appears to be most nearly proportional to the galaxy halo mass M_halo. The mean "absolute" efficiency ratio for GC formation that we derive from the catalog data is M_GCS/M_halo = 6 \times 10^-5. We suggest that the galaxy-to-galaxy scatter around this mean value may arise in part because of differences in the relative timing of GC formation versus field-star formation. Finally, we find that an excellent empirical predictor of total GC population for galaxies of all luminosities is N_GC \sim (R_e \sigma_e)^1.3$, a result consistent with Fundamental Plane scaling relations.