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 x 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 NGC4486. 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) and preliminarily 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 Cgriz´ bands. Our results suggest that the best fit to the GC observed colour histograms is consistent with a genuinely bimodal chemical abundance distribution N_GC(Z). On the other side, each ("blue" and "red") GC subpopulation follows a distinct colour-colour relation.