An optical/NIR survey of globular clusters in early-type galaxies

I. Introduction and data reduction procedures^⋆

¹ Astronomical Institute, University of Utrecht, Princetonplein 5, 3584 Utrecht The Netherlands
e-mail: A.L.Chies@uu.nl
² Department of Physics and Astronomy, McMaster University, Hamilton L8S 4M1, Canada
³ Space Telescope European Coordinating Facility, European Southern Observatory, Garching, Germany
⁴ Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA
⁵ UCO/Lick Observatory, University of California, Santa Cruz, CA 95064, USA

Received: 2 September 2010
Accepted: 1 October 2010

Abstract

Context. The combination of optical and near-infrared (NIR) colours has the potential to break the age/metallicity degeneracy and offers a better metallicity sensitivity than optical colours alone. Previous tudies of extragalactic globular clusters (GCs) with this colour combination, however, have suffered from small samples or have been restricted to a few galaxies.

Aims. We compile a homogeneous and representative sample of GC systems with multi-band photometry to be used in subsequent papers where ages and metallicity distributions will be studied.

Methods. We acquired deep K-band images of 14 bright nearby early-type galaxies. The images were obtained with the LIRIS near-infrared spectrograph and imager at the William Herschel Telescope (WHT) and combined with optical ACS g and z images from the Hubble Space Telescope public archive.

Results. For the first time we present homogeneous GC photometry in this wavelength regime for a large sample of galaxies, 14. We achieved a limiting magnitude of K ~ 20−21. For the majority of the galaxies we detect about 70 GCs each. NGC 4486 and NGC 4649, the cluster-richest galaxies in the sample contain 301 and 167 GCs, respectively. We present tables containing coordinates, photometry and sizes of the GCs.