Publication Date:
2016-02-12
Description:
Galactic nuclei typically host either a nuclear star cluster (NSC, prevalent in galaxies with masses 10 10 M ) or a massive black hole (MBH, common in galaxies with masses 10 12 M ). In the intermediate-mass range, some nuclei host both an NSC and an MBH. In this paper, we explore scaling relations between NSC mass ( ${\cal M}_{\rm NSC}$ ) and host-galaxy total stellar mass ( ${\cal M}_{\star ,\rm gal}$ ) using a large sample of NSCs in late- and early-type galaxies, including a number of NSCs harbouring an MBH. Such scaling relations reflect the underlying physical mechanisms driving the formation and (co)evolution of these central massive objects. We find ~1.5 significant differences between NSCs in late- and early-type galaxies in the slopes and offsets of the relations r eff,NSC – ${\cal M}_{\rm NSC}$ , r eff,NSC – ${\cal M}_{\star ,\rm gal}$ and ${\cal M}_{\rm NSC}$ – ${\cal M}_{\star ,\rm gal}$ , in the sense that (i) NSCs in late types are more compact at fixed ${\cal M}_{\rm NSC}$ and ${\cal M}_{\star ,\rm gal}$ ; and (ii) the ${\cal M}_{\rm NSC}$ – ${\cal M}_{\star ,\rm gal}$ relation is shallower for NSCs in late types than in early types, similar to the ${\cal M}_{\rm BH}$ – ${\cal M}_{\star ,\rm bulge}$ relation. We discuss these results in the context of the (possibly ongoing) evolution of NSCs, depending on host-galaxy type. For NSCs with an MBH, we illustrate the possible influence of an MBH on its host NSC, by considering the ratio between the radius of the MBH sphere of influence and r eff,NSC . NSCs harbouring a sufficiently massive black hole are likely to exhibit surface brightness profile deviating from a typical King profile.
Print ISSN:
0035-8711
Electronic ISSN:
1365-2966
Topics:
Physics
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