Properties of Nuclear Star Clusters in Low Surface Brightness Galaxies

Abstract

Using the Systematically Measuring Ultra-Diffuse Galaxies and Sloan Digital Sky Survey catalogs and our own reprocessing of the Legacy Survey imaging, we investigate the properties of nuclear star clusters (NSCs) in galaxies having central surface brightnesses as low as 27 mag arcsec ^−2 . We identify 273 (123 with known redshift) and 32 NSC-bearing galaxies in the two samples, respectively, where we require candidate NSCs to have a separation of less than 0.10 r _e from the galaxy center. We find that galaxies with low central surface brightness ( μ _0, _g > 24 mag arcsec ^−2 ) are more likely to contain an NSC if they (1) have a higher stellar mass, (2) have a higher stellar-to-total mass ratio, (3) have a brighter central surface brightness, (4) have a larger axis ratio, or (5) lie in a denser environment. Because of the correlations among these various quantities, it is likely that only one or two are true physical drivers. We also find scaling relations for the NSC mass with stellar mass ( M _NSC / ${M}_{\odot }={10}^{6.02\pm 0.03}{({M}_{* ,\mathrm{gal}}/{10}^{8}{M}_{\odot })}^{0.77\pm 0.04}$ ) and halo mass ( M _NSC / ${M}_{\odot }={10}^{6.11\pm 0.05}{({M}_{h,\mathrm{gal}}/{10}^{10}{M}_{\odot })}^{0.92\pm 0.05}$ ), although it is the scaling with halo mass that is consistent with a direct proportionality. In galaxies with an NSC, M _NSC ≈ 10 ^−4 M _h _,gal . This proportionality echoes the finding of a direct proportionality between the mass (or number) of globular clusters (GCs) in galaxies and the galaxy’s total mass. These findings favor a related origin for GCs and NSCs.

Keywords

• Low surface brightness galaxies
• Galaxy properties
• Galaxy structure
• Galaxy nuclei
• Star clusters