The Milky Way like galaxy NGC 6384 and its nuclear star cluster at high NIR spatial resolution using LBT/ARGOS commissioning data

Abstract

We analyse high spatial resolution near infrared (NIR) imaging of NGC 6384, a Milky Way like galaxy, using ARGOS commissioning data at the Large Binocular Telescope (LBT). ARGOS provides a stable PSF FWHM = 0.2"-0.3" AO correction of the ground layer across the LUCI 2 NIR camera 4 × 4 arcmin field by using six laser guide stars (three per telescope) and a natural guide star for tip-tilt sensing and guiding. Enabled by this high spatial resolution, we analyse the structure of the nuclear star cluster (NSC) and the central kiloparsec of NGC 6384. We find via 2D modelling that the NSC (r<SUB>eff</SUB> ≃ 10 pc) is surrounded by a small (r<SUB>eff</SUB> ≃ 100 pc) and a larger Sersić (r<SUB>eff</SUB> ≃ 400 pc), all embedded within the NGC 6384 large-scale boxy/X-shaped bulge and disc. This proof-of-concept study shows that with the high spatial resolution achieved by ground-layer AO we can push such analysis to distances previously only accessible from space. SED-fitting to the NIR and optical HST photometry allowed to leverage the age-metallicity-extinction degeneracies and derive the effective NSC properties of an young to old population mass ratio of 8 per cent with M_{\star ,old} ∼eq 3.5× 10^7 M_☉, Age<SUB>old, young</SUB> = 10.9 ± 1.3 Gyr and 226 Myr ± 62 per cent, metallicity [M/H] = -0.11 ± 0.16, and 0.33± 39 per cent dex, and E(B - V) = 0.63 and 1.44 mag.