The globular cluster populations of giant galaxies: Mosaic imaging of five moderate-luminosity early-type galaxies

Abstract

This paper presents results from wide-field imaging of the globular cluster (GC) systems of five intermediate-luminosity (M V -21 to -22) early-type galaxies. The aim is to accurately quantify the global properties of the GC systems by measuring them out to large radii. We obtained BVR imaging of four lenticular galaxies (NGC5866, NGC4762, NGC4754, NGC3384) and one elliptical galaxy (NGC5813) using the KPNO 4m telescope and Mosaic imager and traced the GC population to projected galactocentric radii ranging from 20kpc to 120kpc. We combine our imaging with Hubble Space Telescope data to measure the GC surface density close to the galaxy center. We calculate the total number of GCs (N GC) from the integrated radial profile and find N GC = 340 ± 80 for NGC5866, N GC = 2900 ± 400 for NGC5813, N GC = 270 ± 30 for NGC4762, N GC = 115 ± 15 for NGC4754, and N GC = 120 ± 30 for NGC3384. The measured GC specific frequencies are S N between 0.6 and 3.6 and T in the range 0.9-4.2. These values are consistent with the mean specific frequencies for the galaxies' morphological types found by our survey and other published data. Three galaxies (NGC5866, NGC5813, and NGC4762) had sufficient numbers of GC candidates to investigate color bimodality and color gradients in the GCsystems. NGC5813 shows strong evidence (>3σ) for bimodality and a B - R color gradient resulting from a more centrally concentrated red (metal-rich) GC subpopulation. We find no evidence for statistically significant color gradients in the other two galaxies. © 2012. The American Astronomical Society. All rights reserved..