Globular Clusters in Virgo Ellipticals: Unexpected Results for Giants and Dwarfs from Advanced Camera for Surveys Imaging

By J. Strader, J. Brodie, Lee R. Spitler, M. Beasley. 2005

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We have analyzed archival Hubble Space Telescope Advanced Camera for Surveys images in g and z of the globular cluster (GC) systems of 53 ellipticals in the Virgo Cluster, spanning massive galaxies to dwarf ellipticals (dEs). Several new results emerged. (1) In the giant ellipticals (gEs) M87 and NGC 4649, there is a correlation between luminosity and color for individual blue (metal-poor) GCs, such that more massive GCs are more red (metal-rich). A plausible interpretation of this result is self-enrichment, and a speculative suggestion is that these GCs once possessed dark matter halos. (2) The dispersion in color is nearly twice as large for the metal-rich GCs as for the metal-poor GCs. However, there is evidence for a nonlinear relation between g - z and metallicity, and the dispersion in metallicity may be the same for both subpopulations. (3) Very luminous, intermediate-color GCs are common in gEs. These objects may be remnants of many stripped dwarfs, analogs of ω Cen in the Galaxy. (4) There is a continuity of GC system colors from gEs to some dEs; in particular, many dEs have metal-rich GC subpopulations. We also confirm the GC color-galaxy luminosity relations found previously for both metal-poor and metal-rich GC subpopulations. (5) There are large differences in GC specific frequency among dEs, independent of the presence of a nucleus and the fraction of metal-rich GCs. Over -15 < MB < -18 we find little correlation between specific frequency and MB. But we do find evidence for two separate SN classes of dEs: those with B-band SN ∼ 2 and those with populous GC systems that have SN ranging from ∼5 to 20 with median SN ∼ 10. Together, these points suggest multiple formation channels for dEs in the Virgo Cluster. (6) The peak of the GC luminosity function (GCLF) is the same for both gEs and dEs. This is contrary to expectations of dynamical friction on massive GCs, unless the primordial GCLF varies between gEs and dEs. Among gEs the GCLF turnover varies by a surprisingly small 0.05 mag, an encouraging result for its use as an accurate standard candle.

Subfields: Astronomy and Astrophysics

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Citations in the corpus

THE NEXT GENERATION VIRGO CLUSTER SURVEY (NGVS). I. INTRODUCTION TO THE SURVEY (2012, background): “…dependence on color index (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…”
The Electromagnetic Counterpart of the Binary Neutron Star Merger LIGO/Virgo GW170817. VII. Properties of the Host Galaxy and Constraints on the Merger Timescale (2017, background): “Strader et al. (2006) found that the luminosity at the peak of the GCLF remains the same regardless of galaxy size for elliptical galaxies.”
The Origin of Dwarf Ellipticals in the Virgo Cluster (2008, background): “The specific frequency of globular clusters in dE galaxies ranges in between ∼ 1 and ∼ 20 with ∼ a double distribution peaked at SN ∼ 2 and SN ∼ 10 (Strader et al. 2006).”
The SLUGGS Survey: kinematics for over 2500 globular clusters in 12 early-type galaxies (2012, background): “…ages (>10 Gyr; Cohen, Blakeslee & Ryzhov 1998; Kissler-Patig et al. 1998; Beasley et al. 2000, 2004; Forbes et al. 2001; Brodie & Larsen 2002; Schroder et al. 2002; Strader et al. 2005) suggest they have survived violent merging events, preserving the chemodynamical record of their parent galaxies.”
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).”