Masses and scaling relations for nuclear star clusters, and their co-existence with central black holes
Abstract
Galactic nuclei typically host either a Nuclear Star Cluster (NSC, prevalent in galaxies with masses $\lesssim 10^{10}M_\odot$) or a Massive Black Hole (MBH, common in galaxies with masses $\gtrsim 10^{12}M_\odot$). In the intermediate mass range, some nuclei host both a NSC and a 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 harboring a MBH. Such scaling relations reflect the underlying physical mechanisms driving the formation and (co)evolution of these central massive objects. We find $\sim\!1.5\sigma$ significant differences between NSCs in late- and early-type galaxies in the slopes and offsets of the relations $r_{\rm eff,NSC}$--${\cal M}_{\rm NSC}$, $r_{\rm eff, NSC}$--${\cal M}_{\star,\rm gal}$ 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 a MBH, we illustrate the possible influence of a MBH on its host NSC, by considering the ratio between the radius of the MBH sphere of influence and $r_{\rm eff, NSC}$. NSCs harbouring a sufficiently massive black hole are likely to exhibit surface brightness profile deviating from a typical King profile.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- April 2016
- DOI:
- 10.1093/mnras/stw093
- arXiv:
- arXiv:1601.02613
- Bibcode:
- 2016MNRAS.457.2122G
- Keywords:
-
- Astrophysics - Astrophysics of Galaxies
- E-Print:
- Accepted in MNRAS, full version of Table A1 is available. 23 pages, 9 figures, Two tables