Globular Cluster Systems in Brightest Cluster Galaxies: Bimodal Metallicity Distributions and the Nature of the High-Luminosity Clusters

By W. Harris, B. Whitmore, D. Karakla, Waldemar M. M. Okoń, W. A. Baum, D. Hanes, J. Kavelaars. 2005

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We present new (B, I) photometry for the globular cluster systems in eight brightest cluster galaxies (BCGs), obtained with the ACS/WFC camera on the Hubble Space Telescope. In the very rich cluster systems that reside within these giant galaxies, we find that all have strongly bimodal color distributions that are clearly resolved by the metallicity-sensitive (B - I) index. Furthermore, the mean colors and internal color range of the blue subpopulation are remarkably similar from one galaxy to the next, to well within the ±0.02-0.03 mag uncertainties in the foreground reddenings and photometric zero points. By contrast, the mean color and internal color range for the red subpopulation differ from one galaxy to the next by twice as much as the blue population. All the BCGs show population gradients, with much higher relative numbers of red clusters within 5 kpc of their centers, consistent with their having formed at later times than the blue, metal-poor population. A striking new feature of the color distributions emerging from our data is that for the brightest clusters (MI < -10.5) the color distribution becomes broad and less obviously bimodal. This effect was first noticed by Ostrov et al. and Dirsch et al. for the Fornax giant NGC 1399; our data suggest that it may be a characteristic of many BCGs and perhaps other large galaxies. Our data indicate that the blue (metal-poor) clusters brighter than MI ≃ -10 become progressively redder with increasing luminosity, following a mass/metallicity scaling relation Z ~ M0.55. A basically similar relation has been found for M87 by Strader et al. (2005). We argue that these GCS characteristics are consistent with a hierarchical-merging galaxy formation picture in which the metal-poor clusters formed in protogalactic clouds or dense starburst complexes with gas masses in the range 107-1010 M☉, but where the more massive clusters on average formed in bigger clouds with deeper potential wells where more preenrichment could occur.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/b9ec28c6853969604749f7e0eae5259b3a27a31d

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Citations in the corpus

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).”
Globular clusters, satellite galaxies and stellar haloes from early dark matter peaks (2005, background): “Observations suggest that the numbers of old globular clusters are correlated with the luminosity of the host galaxy (Harris 1991; McLaughlin 1999; Harris et al. 2006; Rhode, Zepf & Santos 2005).”
Compact binaries in star clusters – I. Black hole binaries inside globular clusters (2009, background): “These two metallicities also fall within the high- and low-mass peaks in the bimodal metallicity distribution found for brightest cluster galaxies by Harris et al. (2006).”
THE RELATIONSHIPS AMONG COMPACT STELLAR SYSTEMS: A FRESH VIEW OF ULTRACOMPACT DWARFS (2011, background): “Among GCs, the blue tilt has been interpreted in terms of self-enrichment (e.g., Harris et al. 2006; Strader et al. 2006; Mieske et al. 2006b; Strader & Smith 2008; Bailin & Harris 2009).”
Extragalactic Globular Clusters and Galaxy Formation (2006, methodology): “(ii) The recently discovered correlation between GC metallicity and mass for bright metal-poor GCs in several massive galaxies (Strader et al. 2006; Harris et al. 2006).”
Star Cluster Demographics. I. A General Framework and Application to the Antennae Galaxies (2006, background): “The difference in the [Fe/H] distribution functions of stars and globular clusters in various galaxies may be due to less effective disruption of the metalpoor clusters (e.g., Fall &Rees 1985; Harris et al. 2006).”
From star clusters to dwarf galaxies: the properties of dynamically hot stellar systems (2008, background): “The GC systems of elliptical galaxies, on the other hand, have a larger fraction of red (probably metal-rich) GCs, which are also somewhat brighter than the blue (probably metal-poor) ones (Harris et al. 2006; Wehner & Harris 2007).”
WIDE-FIELD PRECISION KINEMATICS OF THE M87 GLOBULAR CLUSTER SYSTEM (2011, background): “The possible convergence of the GC color-magnitude distribution to a unimodal distribution at the bright end has been previously discussed in other galaxies by Ostrov, Forte, & Geisler (1998), Dirsch et al. (2003), Harris et al. (2006), Romanowsky et al. (2009), and Forbes et al. (2011).”
From Supermassive Black Holes to Dwarf Elliptical Nuclei: A Mass Continuum (2006, background): “Finally, we point out that this link may provide us with a physical reason for the longobserved upper mass limit of about for old globular710 M, clusters (e.g., Harris et al. 2006).”
THE NEXT GENERATION VIRGO CLUSTER SURVEY (NGVS). I. INTRODUCTION TO THE SURVEY (2012, background): “…(Yoon et al. 2006; Cantiello & Blakeslee 2007); the role of self-enrichment in explaining the GC CMR, i.e., the “blue tilt” (Strader et al. 2006; Harris et al. 2006; Peng et al. 2009); the shape of the cluster luminosity/mass function across galaxies spanning a range in mean age and…”
Globular cluster systems in nearby dwarf galaxies – III. Formation efficiencies of old globular clusters (2010, background): “…limits, adequate spatial coverage etc.) from the literature (Ashman & Zepf 1998; Rhode & Zepf 2001, 2003, 2004; Forbes et al. 2001; Forte et al. 2001; Dirsch et al. 2003, 2005; Gómez & Richtler 2004; Bassino et al. 2006b,a, 2008; Harris et al. 2006; Tamura et al. 2006a,b; Rhode et al. 2007).”