Formation Efficiencies of Old Globular Clusters - from Dwarf to Giant Galaxies

TL;DR

This study examines globular cluster formation efficiencies across a wide range of galaxy types and masses, revealing consistent scaling relations and a typical formation efficiency with notable variations in certain galaxies.

Contribution

It provides a theoretical framework linking globular cluster system properties to galaxy mass and type, with a specific formation efficiency value and explanations for deviations.

Findings

Globular cluster scaling parameters are consistent across galaxy types and environments.

Early-type galaxies have roughly twice the GC system scaling parameter as late-types.

The average GC formation efficiency is about 5.5e-5, with increased scatter in low-mass galaxies.

Abstract

For the full galaxy mass range, we find that previously observed trends of globular cluster (GC) system scaling parameters (number, luminosity or mass of all GCs in a galaxy normalized to the host galaxy luminosity or mass, e.g. S_L) as a function of galaxy mass, holds irrespective of galaxy type or environment. The S_L-value of early-type galaxies is, on average, twice that of late-types. We derive theoretical predictions which describe remarkably well the observed GC system scaling parameter distributions given an assumed GC formation efficiency ({\eta}), i.e. the ratio of total mass in GCs to galaxy halo mass. It has a mean value of {\eta}=5.5e-5 , and an increasing scatter toward low galaxy mass. The excess {\eta}-values of some massive galaxies compared to expectations from the mean model prediction, may be attributed to an efficient GC formation, inefficient production of field stars, accretion of low-mass high-{\eta} galaxies or likely a mixture of all these effects.