The SLUGGS Survey: HST/ACS Mosaic Imaging of the NGC 3115 Globular Cluster System

Abstract

We present HST/ACS $g$ and $z$ photometry and half-light radii $R_{\mathrm{h}}$ measurements of 360 globular cluster (GC) candidates around the nearby S0 galaxy NGC 3115. We also include Subaru/Suprime-Cam $g$, $r$, and $i$ photometry of 421 additional candidates. The well-established color bimodality of the GC system is obvious in the HST/ACS photometry. We find evidence for a "blue tilt" in the blue GCs, wherein the blue GCs get redder as luminosity increases, indicative of a mass-metallicity relationship. We find a color gradient in both the red and blue subpopulations, with each group of clusters becoming bluer at larger distances from NGC 3115. The gradient is of similar strength in both subpopulations, but is monotonic and more significant for the blue clusters. On average, the blue clusters have ~10% larger $R_{\mathrm{h}}$ than the red clusters. This average difference is less than is typically observed for early-type galaxies but does match that measured in the literature for M104, suggesting that morphology and inclination may affect the measured size difference between the red and blue clusters. However, the scatter on the $R_{\mathrm{h}}$ measurements is large. We also identify 31 clusters more extended than typical GCs, which we consider ultra-compact dwarf (UCD) candidates. Many of these objects are fainter than typical UCDs. While it is likely that a significant number will be background contaminants, six of these UCD candidates are spectroscopically confirmed. To explore low-mass X-ray binaries in the GC system, we match our ACS and Suprime-Cam detections to corresponding Chandra X-ray sources. We identify 45 X-ray - GC matches, 16 among the blue subpopulation and 29 among the red subpopulation. These X-ray/GC coincidence fractions are larger than is typical for most GC systems, probably due to the increased depth of the X-ray data compared to previous studies of GC systems.

16 Pages, 14 Figures, 3 Tables. Accepted to AJ

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Cited by in corpus (9)

• The SAGES Legacy Unifying Globulars and GalaxieS Survey (SLUGGS): Sample definition, methods, and initial results
• Globular Cluster Systems in Brightest Cluster Galaxies. III: Beyond Bimodality
• The SLUGGS survey: Globular cluster stellar population trends from weak absorption lines in stacked spectra
• The SLUGGS Survey: a catalog of over 4000 globular cluster radial velocities in 27 nearby early-type galaxies
• Detection of a distinct metal-poor stellar halo in the early-type galaxy NGC 3115
• The Next Generation Virgo Cluster Survey. XXXIV. Ultra-Compact Dwarf (UCD) Galaxies in the Virgo Cluster
• NGC 5128 globular cluster candidates out to 150 kpc: a comprehensive catalog from Gaia and ground based data
• The assembly history of the nearest S0 galaxy NGC 3115 from its kinematics out to six half-light radii
• Recovering the origins of the lenticular galaxy NGC 3115 using multi-band imaging