The Globular Cluster Systems of the Early-Type Galaxies NGC 3379, NGC 4406, and NGC 4594 and Implications for Galaxy Formation

Abstract

We have investigated the global properties of the globular cluster (GC) systems of three early-type galaxies: the Virgo cluster elliptical NGC 4406, the field elliptical NGC 3379, and the field S0 galaxy NGC 4594. These galaxies were observed as part of a wide-field CCD survey of the GC populations of a large sample of normal galaxies beyond the Local Group. Images obtained with the Mosaic detector on the Kitt Peak 4-m telescope provide radial coverage to at least 24 ′ , or ∼70−100 kpc. We use BV R photometry and image classification to select GC candidates and thereby reduce contamination from non-GCs, and HST WFPC2 data to help quantify the contamination that remains. The GC systems of all three galaxies have color distributions with at least two peaks and show modest negative color gradients. The proportions of blue GCs range from 60−70% of the total populations. The GC specific frequency (S N ) of NGC 4406 is 3.5±0.5, ∼20% lower than past estimates and nearly identical to S N for the other Virgo cluster elliptical included in our survey, NGC 4472. S N for NGC 3379 and NGC 4594 are 1.2±0.3 and 2.1±0.3, respectively; these are similar to past values but the errors have been reduced by a factor of 2−3. We compare our results for the early-type sample (including NGC 4472) to models for the formation of massive galaxies and their GC systems. Of the scenarios we consider, a hierarchical merging picture -in which metal-poor GCs form at high redshift in protogalactic building blocks and metal-rich GC populations are built up over time during subsequent gas-rich mergers -appears most consistent with the data.the GC systems, such as overall mean colors, total numbers, and specific frequencies, making these values subject to considerable uncertainties. Well-constrained global values are what is needed to test the model predictions as well as to improve our overall understanding of GC systems and their relationship to galaxy formation. Accordingly, we have observed the GC systems of a large sample of both early-type and spiral galaxies. The survey employs wide-field CCD imaging to observe the full extent of the galaxy GC systems, good resolution to help eliminate background galaxies from the GC candidate lists, and three-color photometry to isolate bona fide GCs from contaminating stars and galaxies. In addition, archival Hubble Space Telescope (HST) images are available for most of the targets; these data are used to help quantify the level of contamination in the GC lists.

Globular cluster systems of six shell galaxies

“…Data on the slope in the outer regions of our most distant galaxy, NGC 7626, and surface density profiles in the literature, support this assumption (e.g. Rhode & Zepf 2004;Zepf et al 1994;Harris et al 2000). Finally, for NGC 3923, wide field data ) show a constant slope to a radius of 5.6 arcmin ( 34 kpc).…”

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

“…Similar results were found by Kundu & Whitmore (2001) (with V − I photometry) and Peng et al (2006). It was also studied with B, V and R photometry, by Rhode & Zepf (2004) who reported a multimodal colour distribution. It hosts a KDC (Bender 1998).…”

The globular cluster systems of Abell 1185

“…In reality, however, such constraints are likely to be weak because of degenerate dependencies of globular cluster colors on galactocentric distances and host galaxy properties. A preponderance of blue IGCs could arise, for example, if the majority came from dwarf galaxies that were tidally disrupted or if they were stripped from the outer halos of giant galaxies whose globular clusters are bluer on average than their counterparts closer to the galaxy center (Geisler et al 1996;Rhode & Zepf 2004;Bassino et al 2006;Tamura et al 2006). Nevertheless, if the globular clusters are found to have a distinctive color distribution then this could be an important clue to their origin.…”