Nonlinear color-metallicity relations of globular clusters. IV. testing the nonlinearity scenario for color bimodality via HST/WFC3 u-band photometry of M84 (NGC 4374)

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  1. Get@NRC: Nonlinear color-metallicity relations of globular clusters. IV. testing the nonlinearity scenario for color bimodality via HST/WFC3 u-band photometry of M84 (NGC 4374) (Opens in a new window)
DOIResolve DOI: http://doi.org/10.1088/0004-637X/768/2/137
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TypeArticle
Journal titleThe Astrophysical Journal
ISSN0004-637X
Volume768
Issue2
Article number137
AbstractColor distributions of globular clusters (GCs) in most massive galaxies are bimodal. Assuming linear color-to-metallicity conversions, bimodality is viewed as the presence of merely two GC subsystems with distinct metallicities, which serves as a critical backbone of various galaxy formation theories. Recent studies, however, revealed that the color-metallicity relations (CMRs) often used to derive GC metallicities (e.g., CMRs of g-z, V-I, and C-T1) are in fact inflected. Such inflection can create bimodal color distributions if the underlying GC metallicity spread is simply broad as expected from the hierarchical merging paradigm of galaxy formation. In order to test the nonlinear-CMR scenario for GC color bimodality, the u-band photometry is proposed because the u-related CMRs (e.g., CMRs of u-g and u-z) are theoretically predicted to be least inflected and most distinctive among commonly used optical CMRs. Here, we present Hubble Space Telescope (HST)/WFC3 F336W (u-band) photometry of the GC system in M84, a giant elliptical in the Virgo galaxy cluster. Combining the u data with the existing HST ACS/WFC g and z data, we find that the u-z and u-g color distributions are different from the g-z distribution in a very systematic manner and remarkably consistent with our model predictions based on the nonlinear-CMR hypothesis. The results lend further confidence to the validity of the nonlinear-CMR scenario as an explanation for GC color bimodality. There are some GC systems showing bimodal spectroscopic metallicity, and in such systems the inflected CMRs often create stronger bimodality in the color domain. © 2013. The American Astronomical Society. All rights reserved.
Publication date
LanguageEnglish
AffiliationNational Research Council Canada (NRC-CNRC); NRC Herzberg Institute of Astrophysics (HIA-IHA)
Peer reviewedYes
NPARC number21269588
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Record identifier626fea4c-4d65-49eb-adff-2c3b037c1829
Record created2013-12-13
Record modified2016-07-18
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