The Next Generation Virgo Cluster Survey (NGVS). XXIX. Demography of Nuclear Star Clusters

Abstract

Nuclear star clusters (NSCs) provide insights into processes shaping galaxy cores. We use deep $u^*giz$ CFHT imaging from the Next Generation Virgo Cluster Survey (NGVS) to study NSCs in Virgo cluster galaxies. Our parent sample consists of 3680 certain, likely or possible cluster members spanning more than six orders of magnitude in stellar mass. Using a self-consistent classification framework, we identify 1144 candidate nucleated galaxies: 804 high-confidence NSCs and 340 lower-confidence candidates. This is the largest and most uniform NSC catalog for any environment studied to date. We explore the nucleation fraction, $f_{\rm nuc}$, as a function of stellar mass, morphology and environment. Consistent with previous studies, we find stellar mass a key factor driving nucleation probability. However, host-galaxy morphology is also important, with the peak of the $f_{\rm nuc}$ distribution occurring at progressively lower masses as one moves from later to earlier morphological types. We interpret this shift as evidence that the more extended structures of late-type galaxies reduce the efficiency of GC inspiral at fixed stellar mass, while gas-rich secular processes and central star formation may contribute increasingly to NSC growth at higher masses. Environment plays a smaller role, with only a slight enhancement in high-density regions. We characterize the nonlinear relationship between NSC stellar mass and host-galaxy mass, and assess the role of selection effects. We conclude that NSC formation is best explained by a hybrid scenario, with inspiraling star clusters and in situ star formation contributing, and their relative importance dictated primarily by galaxy mass.