Globular clusters of NGC 3115 in the near-infrared

Demonstrating the correctness of two opposing scenarios^{⋆,⋆⋆,⋆⋆⋆}

¹ INAF, Osservatorio Astronomico di Teramo, via Maggini, 64100 Teramo, Italy
e-mail: cantiello@oa-teramo.inaf.it
² Dominion Astrophysical Observatory, Herzberg Institute of Astrophysics, NRC of Canada, Victoria, Canada
³ School of Physics and Astronomy, University of Nottingham, University Park, Nottingham NG7 2RD, UK
⁴ University of California Observatories, Santa Cruz, CA 95064, USA
⁵ Max Planck Institut fur Astronomie, Konigstuhl 17, 69117, Heidelberg, Germany
⁶ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany

Received: 18 December 2013
Accepted: 17 February 2014

Abstract

We combined new near-infrared VLT/HAWK-I data of the globular clusters (GCs) in the isolated edge-on S0 galaxy NGC 3115 with optical and spectroscopic ones taken from the literature, with the aim of analyzing the multiband GC color distributions. A recent study from the SLUGGS survey has shown that the GCs in this galaxy follow a bimodal distribution of Ca II triplet indices. Thus, NGC 3115 presents a critical example of a GC system with multiple, distinct, metallicity subpopulations, and this may argue against the “projection” scenario, which posits that the ubiquitous color bimodality mainly results from nonlinearities in the color-metallicity relations. Using optical, NIR, and spectroscopic data, we found strong and consistent evidence of index bimodality, which independently confirms the metallicity bimodality in NGC 3115 GCs. At the same time, we also found evidence for some color–color nonlinearity. Taken in the broader context of previous studies, the multicolor consistency of the GC bimodality in NGC 3115 suggests that in cases where GC systems exhibit clear differences between their optical and optical-NIR color distributions (as in some giant ellipticals), the apparent inconsistencies most likely result from nonlinearities in the color-metallicity relations.