How large are the globular cluster systems of early-type galaxies and do they scale with galaxy halo properties?

TL;DR

This study quantifies the size of globular cluster systems in early-type galaxies, revealing they typically extend about four times the galaxy size and scale with halo properties, with implications for galaxy formation models.

Contribution

It provides the first comprehensive analysis of GC system sizes in relation to host galaxy halo properties across a range of galaxy types and masses.

Findings

GC systems extend about 4 times the host galaxy size

GC system size scales linearly with halo virial radius

Scaling relations hold for ultra diffuse galaxies and Milky Way

Abstract

The globular cluster systems of galaxies are well-known to extend to large galactocentric radii. Here we quantify the size of GC systems using the half number radius of 22 GC systems around early-type galaxies from the literature. We compare GC system sizes to the sizes and masses of their host galaxies. We find that GC systems typically extend to 4$\times$ that of the host galaxy size, however this factor varies with galaxy stellar mass from about 3$\times$ for M$^{\ast}$ galaxies to 5$\times$ for the most massive galaxies in the universe. The size of a GC system scales approximately linearly with the virial radius (R$_{200}$) and with the halo mass (M$_{200}$) to the 1/3 power. The GC system of the Milky Way follows the same relations as for early-type galaxies. For Ultra Diffuse Galaxies their GC system size scales with halo mass and virial radius as for more massive, larger galaxies. UDGs indicate that the linear scaling of GC system size with stellar mass for massive galaxies flattens out for low stellar mass galaxies. Our scalings are different to those reported recently by Hudson \& Robison (2017).