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

¹ Departamento de Física y Astronomía, Facultad de Ciencias, Universidad de Valparaíso. Av. Gran Bretaña 1111, Valparaíso, Chile e-mail: mmora@dfa.uv.cl
² European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany e-mail: mkissler@eso.org
³ Astronomical Institute, University of Utrecht, Princetonplein 5, 3584 CC, Utrecht, The Netherlands e-mail: S.S.Larsen@uu.nl

Received: 28 April 2008
Accepted: 24 July 2008

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, and Hδ and the combined [MgFe]' index, we found that the globular clusters are metal-poor [Z/H] 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.