Color-metallicity relations. II. M87 GCs

In essence, a color distribution of GCs is a "projected" distribution of their metallicities. Since the form of CMRs hinges on which color is used, the shape of color distributions varies depending significantly on the colors.

Among other optical colors, the u-band related colors (e.g., u-g and u-z) are theoretically predicted to exhibit significantly less inflected CMRs than other preferred CMRs (e.g., for g-z). As a case study, we performed the Hubble Space Telescope (HST)/WFPC2 archival u-band photometry for the M87 (NGC 4486) GC system with confirmed color bimodality. We show that the u-band color distributions are significantly different from that of g-z and consistent with our model predictions.