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

TL;DR

This study confirms the nature and properties of globular clusters in the low-luminosity spiral galaxy NGC 45, revealing their metallicities, ages, and kinematics, which shed light on galaxy formation processes.

Contribution

First spectroscopic confirmation of globular clusters in a low-luminosity spiral galaxy and analysis of their metallicities, ages, and kinematics.

Findings

Globular clusters are metal-poor with [Z/H]<=-0.33 dex.

Clusters exhibit halo or bulge-like kinematics with little rotation.

Globular clusters likely formed during galaxy assembly.

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 [alpha/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 H_beta, H_gamma, and H_delta and the combined [MgFe]' index, we found that the globular clusters are metal-poor [Z/H]<=-0.33 dex and [alpha/Fe]<=0.0 element ratio. These results argue in favor of a population of globular clusters formed during the assembling of the galaxy.