Multicolour-metallicity Relations from Globular Clusters in NGC 4486 (M87)

TL;DR

This study uses multicolor photometry of globular clusters in NGC 4486 to establish color-metallicity relations, revealing bimodal chemical abundance distributions and distinct color-color relations for subpopulations.

Contribution

It introduces a self-consistent multicolor grid and calibrates color-chemical abundance relations using new and existing photometry, advancing understanding of GC metallicity distributions.

Findings

Bimodal chemical abundance distribution in GCs

Distinct color-color relations for blue and red subpopulations

Multicolor photometry effectively models GC metallicity distributions

Abstract

We present Gemini griz photometry for 521 globular cluster (GC) candidates in a 5.5 x 5.5 arcmin field centered 3.8 arcmin to the south and 0.9 arcmin to the west of the center of the giant elliptical galaxy NGC 4486. All these objects have previously published (C-T1) photometry. We also present new (C-T1) photometry for 338 globulars, within 1.7 arcmin in galactocentric radius, which have (g-z) colors in the photometric system adopted by the Virgo Cluster Survey of the Advanced Camera for Surveys of the Hubble Space Telescope. These photometric data are used to define a self-consistent multicolor grid (avoiding polynomial fits) and preliminary calibrated in terms of two chemical abundance scales. The resulting multicolor color-chemical abundance relations are used to test GC chemical abundance distributions. This is accomplished by modelling the ten GC color histograms that can be defined in terms of the Cgriz bands. Our results suggest that the best fit to the GC observed color histograms is consistent with a genuinely bimodal chemical abundance distribution NGC(Z). On the other side, each (blue and red) GC subpopulation follows a distinct color-color relation.