Spatially Resolving the Star Formation Histories of Three Nearby Nuclear Star Clusters

Abstract

The formation of nuclear star clusters (NSCs) remains an open question. In this work, we use spatially resolved HST /STIS spectroscopic observations of three nearby NSCs (hosted by NGC 5102, NGC 5206, and NGC 205) to constrain their formation histories by exploring radial variations of the stellar populations within each cluster. Utilizing full-spectrum fitting, we find substantial age and metallicity gradients within the central 0. 9 (16 pc) of the NSC in NGC 5102 where populations near the center are young/metal-rich (age ∼400 Myr and [M/H] ∼-0.4) and become older/metal-poor at larger radii (mean age ∼1 Gyr and mean [M/H] ∼-1.6 in the radial range [0. 3, 0. 9]). This behavior suggests that the young/metal-rich population at the center was formed from a period of in situ formation, while the older/metal-poor populations were likely formed by inspiraled globular clusters. The two broad populations observed in the NGC 5102 NSC (young/metal-rich and old/metal-poor) appear to be linked to the transition between the two morphological components of the NSC derived from the surface-brightness profile in Nguyen et al. (2018). The radial ranges explored in NGC 5206 and NGC 205 were much smaller due to poor data quality; in NGC 5206 we find a similar metallicity gradient to NGC 5102 (but with much lower significance), while the data for NGC 205 is too poor to reach any conclusions. Overall, this data highlights the links between the morphological and stellar population complexity of NSCs and their formation mechanisms.

Massive Black Hole Formation in Dense Stellar Environments: Enhanced X-Ray Detection Rates in High-velocity Dispersion Nuclear Star Clusters

“…There are two main proposed channels for the formation of NSCs: globular cluster infall due to dynamical friction (Tremaine et al 1975;Lotz et al 2001;Capuzzo-Dolcetta & Miocchi 2008;Agarwal & Milosavljević 2011;Gnedin et al 2014) and in situ star formation (Seth et al 2006;Walcher et al 2006). In practice, there are likely contributions from both channels, as NSCs have been found to contain multiple stellar populations (Carson et al 2015;Neumayer et al 2020;Fahrion et al 2021;Hannah et al 2021). The relative contribution of each channel likely depends on galaxy mass and environment (Hoyer et al 2021).…”

Massive black hole formation in dense stellar environments: Enhanced X-ray detection rates in high velocity dispersion nuclear star clusters

“…There are two main proposed channels for the formation of NSCs: globular cluster infall due to dynamical friction (Tremaine et al 1975;Lotz et al 2001;Capuzzo-Dolcetta & Miocchi 2008;Agarwal & Milosavljević 2011;Gnedin et al 2014) and in situ star formation (Walcher et al 2006;Seth et al 2006). In practice, there are likely contributions from both channels, as NSCs have been found to contain multiple stellar populations (Carson et al 2015;Neumayer et al 2020;Fahrion et al 2021;Hannah et al 2021). The relative contribution of each channel likely depends on galaxy mass and environment (Hoyer et al 2021).…”