Spectroscopy of globular clusters in the low-luminosity spiral galaxy NGC 45

Abstract

Context. Extragalactic globular clusters have been studied in elliptical galaxies and in a few luminous spiral galaxies, but little is known about globular clusters in low-luminosity spirals. Aims. Past observations with the ACS have shown that NGC 45 hosts a large population of globular clusters (19), as well as several young star clusters. In this work we aim to confirm the bona fide globular cluster status for 8 of 19 globular cluster candidates and to derive metallicities, ages, and velocities. Methods. VLT/FORS2 multislit spectroscopy in combination with the Lick/IDS system was used to derive velocities and to constrain metallicities and [α/Fe] element ratio of the globular clusters. Results. We confirm the 8 globular clusters as bona fide globular clusters. Their velocities indicate halo or bulge-like kinematics, with little or no overall rotation. From absorption indices such as Hβ, Hγ, andHδ and the combined [MgFe] index, we found that the globular clusters are metal-poor [Z/H] ≤ −0.33 dex and [α/Fe] ≤ 0.0 element ratio. These results argue in favor of a population of globular clusters formed during the assembling of the galaxy.