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

FORTE, J.C.; FAIFER, F.R; VEGA, E.I.; BASSINO, L.P.; SMITH CASTELLI, A. V.; CELLONE, S.A.; GEISLER, D.

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2013 vol. 431 p. 1405 - 1416

0035-8711

We present Gemini griz photometry for 521 globular cluster (GC) candidates in a 5.5 × 5.5 arcmin field centred 3.8 arcmin to the south and 0.9 arcmin to the west of the centre 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) colours in the photometric system adopted by the Virgo Cluster Survey of the Advanced Camera for Surveys of the Hubble Space Telescope (HST). These photometric data are used to define a self-consistent multicolour grid (avoiding polynomial fits), including the optical (B-I) (Johnson system) and the (I-H) infra-red (HST system) indices, and tentatively calibrated in terms of two chemical abundance scales. The resulting multicolour colour-chemical abundance relations are used to test GC chemical abundance distributions. This is accomplished by modelling the ten GC colour histograms that can be defined in terms of the C-griz bands. The results show that the best fit to the GC observed colour histograms is achieved by adopting a genuinely bimodal chemical abundancedistribution NGC (Z). In this approach, each ("red" and "blue") GC subpopulation follows a distinct colour-colour relation.