A Hurdle Model for Old Star Clusters and their Host Galaxies
Conference
64th ISI World Statistics Congress - Ottawa, Canada
Format: IPS Abstract
Keywords: bayesian hierarchical model, measurement error, physical
Session: IPS 266 - Statistics for Astronomy
Wednesday 19 July 10 a.m. - noon (Canada/Eastern)
Abstract
Almost every galaxy in the universe has a population of old star clusters, called Globular Clusters (GCs). Previous works show that the stellar mass of GCs in a galaxy is linearly correlated (in log space) with the host galaxy's mass. However, this empirical relation breaks down for small, dwarf galaxies --- in fact, some dwarf galaxies do not have GCs at all. Moreover, these "zeros" in the data (galaxies without GCs) have traditionally been ignored when fitting the linear relationship. This is unfortunate, as the transition region in mass over which galaxies go from having GCs to not having them could have important implications for GC and galaxy formation theories. Thus, our research addresses this problem through a Hierarchical, errors-in-variables hurdle ("HERBAL") model that accounts for galaxies with and without GC populations. In this talk, I will discuss the statistical details of our empirical model (which includes measurement uncertainties), the results when applied to data from the very nearby universe, and implications on physical theories of GCs and galaxies.