New Insights from HST Studies of Globular Cluster Systems. I. Colors, Distances, and Specific Frequencies of 28 Elliptical Galaxies

By A. Kundu, B. Whitmore. 2001

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We present an analysis of the globular cluster systems of 28 elliptical galaxies using archival WFPC2 images in the V and I bands. The V-I color distributions of at least 50% of the galaxies appear to be bimodal at the present level of photometric accuracy. We argue that this is indicative of multiple epochs of cluster formation early in the history of these galaxies, possibly due to mergers. We also present the first evidence of bimodality in low-luminosity galaxies and discuss its implication on formation scenarios. The mean color of the 28 cluster systems studied by us is V-I = 1.04 ± 0.04 (0.01) mag corresponding to a mean metallicity of Fe/H = -1.0 ± 0.19 (0.04). We find that the turnover magnitudes of the globular cluster luminosity functions (GCLF) of our sample are in excellent agreement with the distance measurements using other methods and conclude that the accuracy of the GCLF is at least as good as the surface brightness fluctuation method. The absolute magnitude of the turnover luminosity of the GCLF is M = -7.41 (0.03) in V and M = -8.46 (0.03) in I. The mean local specific frequency of our sample of elliptical galaxies within the WFPC2 field-of-view is 2.4 ± 1.8 (0.4), considerably higher than the 1.0 ± 0.6 (0.1) derived for a comparable sample of S0s in a similar analysis. It shows no obvious correlation with metallicity, host galaxy mass or membership in a galaxy cluster. The median size of clusters in all galaxies appears to be remarkably constant at ∼2.4 pc. We suggest that in the future it might be possible to use the sizes of clusters in the inner regions of galaxies as a simple geometrical distance indicator.

Subfields: Astronomy and Astrophysics, Instrumentation, Statistical and Nonlinear Physics

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Citations in the corpus

The structure and environment of young stellar clusters in spiral galaxies (2003, background): “For globular clusters around early-type galaxies, typical effective radii are again 3–4 pc with no clear size-mass correlation (e.g. Kundu & Whitmore 2001).”
The Colors of Dwarf Elliptical Galaxy Globular Cluster Systems, Nuclei, and Stellar Halos (2004, methodology): “Most of the dE GCCs are as blue in V −I as the metal-poor globular clusters in the Milky Way and other bright galaxies (Harris 1991; Forbes & Forte 2000; Kundu & Whitmore 2001).”
The ACS Virgo Cluster Survey. X. Half-Light Radii of Globular Clusters in Early-Type Galaxies: Environmental Dependencies and a Standard Ruler for Distance Estimation (2005, methodology): “Recently, Kundu & Whitmore (2001) used archival HST/WFPC2 observations for a sample of 28 galaxies to argue that the median half-light radii for GCs in early-type galaxies is constant at 〈rh〉 = 2.36± 0.4 pc.”
Globular Clusters in Virgo Ellipticals: Unexpected Results for Giants and Dwarfs from Advanced Camera for Surveys Imaging (2005, methodology): “Luminosity Functions Many previous studies have shown (e.g., Harris 1991; Secker 1992; Kundu & Whitmore 2001; Larsen et al. 2001) that the GCLF in massive galaxies is well fit by a Gaussian or t5 distribution with similar properties among well-studied galaxies:MV 7:4, V 1:3.”
A CATALOG OF GLOBULAR CLUSTER SYSTEMS: WHAT DETERMINES THE SIZE OF A GALAXY'S GLOBULAR CLUSTER POPULATION? (2013, background): “…galaxies (Peng et al. 2006), the Fornax cluster (Villegas et al. 2010), nearby dwarf galaxies (Lotz et al. 2004; Georgiev et al. 2008, 2009), nearby E and S0 galaxies (Kundu & Whitmore 2001a,b; Larsen et al. 2001), and supergiant E galaxies (Blakeslee 1997, 1999; Harris et al. 2006; Harris 2009).”
Extragalactic Globular Clusters and Galaxy Formation (2006, methodology): “Taking advantage of deeper data, Larsen et al. (2001a) and Kundu & Whitmore (2001a) found statistically significant bimodality in most of their sample galaxies, the majority of which were of earlytype.”
The Globular Cluster System of NGC 1399. I. A Wide-Field Photometric Study (2003, background): “It has now emerged from numerous studies (e.g., Kundu & Whitmore 2001a, 2001b; Larsen et al. 2001; Gebhardt & Kissler-Patig 1999; Geisler, Lee, & Kim 1996; Whitmore & Schweizer 1995; Zepf & Ashman 1993) that GCSs of early-type galaxies are by no means homogeneous populations but exhibit…”
The ACS Virgo Cluster Survey. XII. The Luminosity Function of Globular Clusters in Early-Type Galaxies (2007, background): “…(18) While it has been reported before that there is a tendency for the GCLFs in lower luminosity galaxies to show somewhat lower dispersions (e.g., Kundu & Whitmore 2001a), the homogeneity of our sample and analysis make this the most convincing demonstration to date of the existence of a…”
THE NEXT GENERATION VIRGO CLUSTER SURVEY (NGVS). I. INTRODUCTION TO THE SURVEY (2012, methodology): “The power of high-quality, homogeneous imaging for star clusters in large samples of galaxies was demonstrated by early archival programs with HST (Gebhardt & Kissler-Patig 1999; Kundu & Whitmore 2001; Larsen et al. 2001).”
On the formation of globular cluster systems in a hierarchical Universe (2002, background): “…metallicities of GC systems (and their sub-populations) correlate with host galaxy luminosity has been a controversial one (e.g. Brodie & Huchra 1990; Ashman & Bird 1993; Secker et al. 1995; Durrell et al. 1996; Forbes et al. 1996; Kundu & Whitmore 2001; Forbes & Forte 2001; Larsen et al. 2001).”
The ACS Virgo Cluster Survey. I. Introduction to the Survey (2004, methodology): “This latter filter/camera combination is the most commonly used in previous HST studies of extragalactic GC systems and SBF measurements (e.g., Gebhardt & Kissler-Patig 1999; Kundu & Whitmore 2001; Larsen et al. 2001; Ajhar et al. 1997; Neilsen & Tsvetanov 2000).”
Globular Cluster Systems in Brightest Cluster Galaxies: Bimodal Metallicity Distributions and the Nature of the High-Luminosity Clusters (2005, background): “…with HST (for example, Whitmore et al. 1995; Neilsen & Tsvetanov 1999; Gebhardt & Kissler-Patig 1999; Grillmair et al. 1999; Kundu et al. 1999; Kundu & Whitmore 2001; Larsen et al. 2001) and with wide-field ground-based cameras (Geisler et al. 1996; Harris, Harris, & Geisler 2004; Dirsch et…”