Masses and Scaling Relations for Nuclear Star Clusters, and their Coexistence with Central Black Holes

Iskren Y. Georgiev; Torsten Böker; Natan Leigh; Nora Lützgendorf; Nadine Neumayer

doi:10.1093/mnras/stw093

paper

Masses and Scaling Relations for Nuclear Star Clusters, and their Coexistence with Central Black Holes

arXiv:1601.02613 · doi:10.1093/mnras/stw093

Abstract

Galactic nuclei typically host either a Nuclear Star Cluster (NSC, prevalent in galaxies with masses $≲ 1 0^{10} M_{⊙}$ ) or a Massive Black Hole (MBH, common in galaxies with masses $≳ 1 0^{12} M_{⊙}$ ). In the intermediate mass range, some nuclei host both a NSC and a MBH. In this paper, we explore scaling relations between NSC mass ( $M_{NSC}$ ) and host galaxy total stellar mass ( $M_{⋆, gal}$ ) 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 $\sim 1.5 σ$ significant differences between NSCs in late- and early-type galaxies in the slopes and offsets of the relations $r_{eff, NSC}$ -- $M_{NSC}$ , $r_{eff, NSC}$ -- $M_{⋆, gal}$ and $M_{NSC}$ -- $M_{⋆, gal}$ , in the sense that $i)$ NSCs in late-types are more compact at fixed $M_{NSC}$ and $M_{⋆, gal}$ ; and $ii)$ the $M_{NSC}$ -- $M_{⋆, gal}$ relation is shallower for NSCs in late-types than in early-types, similar to the $M_{BH}$ -- $M_{⋆, bulge}$ 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 $r_{eff, NSC}$ . NSCs harbouring a sufficiently massive black hole are likely to exhibit surface brightness profile deviating from a typical King profile.

Accepted in MNRAS, full version of Table A1 is available. 23 pages, 9 figures, Two tables

Masses and Scaling Relations for Nuclear Star Clusters, and their Coexistence with Central Black Holes

Abstract

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