|
Description
Using 3.6{mu}m images of 97 early-type galaxies, we develop and verify methodology to measure globular cluster populations from the S^4^G survey images. We find that (1) the ratio, T_N_, of the number of clusters, N_CL_, to parent galaxy stellar mass, M_*_, rises weakly with M_*_ for early-type galaxies with M_*_>10^10^M_{sun}_ when we calculate galaxy masses using a universal stellar initial mass function (IMF) but that the dependence of T_N_ on M_*_ is removed entirely once we correct for the recently uncovered systematic variation of IMF with M_*_; and (2) for M_*_<10^10^M_{sun}_, there is no trend between N_CL_ and M_*_, the scatter in T_N_is significantly larger (approaching two orders of magnitude), and there is evidence to support a previous, independent suggestion of two families of galaxies. The behavior of N_CL_ in the lower-mass systems is more difficult to measure because these systems are inherently cluster-poor, but our results may add to previous evidence that large variations in cluster formation and destruction efficiencies are to be found among low-mass galaxies. The average fraction of stellar mass in clusters is ~0.0014 for M_*_>10^10^M_{sun}_ and can be as large as ~0.02 for less massive galaxies. These are the first results from the S^4^G sample of galaxies and will be enhanced by the sample of early-type galaxies now being added to S^4^G and complemented by the study of later-type galaxies within S^4^G.
|
