Nuclear Star Clusters in Edge-on Galaxies [chapter]

Anil C. Seth, Julianne J. Dalcanton, Paul W. Hodge, Victor P. Debattista
Globular Clusters - Guides to Galaxies  
From observations of edge-on, late-type galaxies, we present morphological evidence that some nuclear star clusters have experienced in situ star formation. We find three nuclear clusters that, viewed from the edge-on perspective, have both a compact disk-like component and a spheroidal component. In each cluster, the disk components are closely aligned with the major axis of the host galaxy and have bluer colors than the spheroidal components. We spectroscopically verify that one of the
more » ... t one of the observed multiple component clusters has multiple generations of stars. These observations lead us to suggest a formation mechanism for nuclear star clusters, in which stars episodically form in compact nuclear disks, and then lose angular momentum, eventually forming an older spheroid. The full results of this study can be found in a forthcoming paper. Background Nuclear star clusters are a common feature of dwarf elliptical and spiral galaxies. Surveys of both face-on bulgeless spirals (type Scd and later) and dwarf ellipticals find that roughly 75% have a single bright star cluster as their nuclei [2, 5] . The sizes of these nuclear clusters are similar to Galactic globular clusters (r ef f ∼ 3 pc), but they are significantly brighter, with absolute I-band magnitudes of -8 to -16 [2, 3] . This luminosity is due both to their high masses (typically a few ×10 6 M ⊙ ) and to the presence of younger stellar populations [14, 15] . Nuclear clusters are interesting objects in a galaxy evolution context. A number of groups have recently shown that the masses of nuclear clusters correlate with their host galaxy masses along the same relation found for supermassive black holes, and thus appear to be directly connected to the process of galaxy formation [6, 10, 16] . Furthermore, observations of nuclear clusters may provide clues to the formation of unseen supermassive black
doi:10.1007/978-3-540-76961-3_46 fatcat:w25j36venzczdmpba3fr2fschy