Isolated ellipticals and their globular cluster systems

I. Washington photometry of NGC 3585 and NGC 5812^⋆

¹ Departamento de Astronomía Universidad de Concepción, Casilla 160 C, Concepción, Chile
e-mail: rlane@astro-udec.cl
² Finnish Centre for Astronomy with ESO, University of Turku, Väisäläntie 20, 21500 Piikkiö, Finland

Received: 14 August 2012
Accepted: 6 December 2012

Abstract

The globular cluster (GC) systems of isolated elliptical galaxies have only recently begun to be studied in detail, and may exhibit morphological connections to the evolutionary histories of their hosts. Here we present the first in a series of wide-field analyses of the GC systems of the isolated ellipticals – Washington C and R photometry of NGC 3585 and NGC 5812 down to R ~ 24 mag. The GC systems are characterised, with each system displaying both the “Universal” blue peak at (C − R) ~ 1.3, and a red peak, but each with differing strengths. The total number of GCs in each system, and their specific frequencies, are estimated. The GC colours and specific frequencies are highly indicative that the host galaxy environment plays a role in shaping its GC system. We produce, and subtract, accurate models of each galaxy, revealing interesting underlying features, including the first definitive evidence that NGC 5812 is interacting with a dwarf companion galaxy. From the galaxy models we also determine surface brightness and colour profiles. Both colour profiles appear quite flat and with (C − R) ~ 1.7 and we discuss the apparent youth of NGC 3585 in the context of this work.