‘inflected’) can eventually lead to GC bimodal colour distributions, even when a unimodal chemical abundance distribution is assumed (see, for example, Yoon et al. ( 2012) who adopt broken line fits.Ī clarification of the colour–abundance connection is required, since some non-linear relations (e.g. A recent contribution on this subject has been presented by Usher et al. ( 2012).Ī survey of the literature reveals numerous attempts to link colours and chemical abundance, ranging from linear (Geisler & Forte 1990), quadratic (Harris & Harris 2002 Forte, Faifer & Geisler 2007 Moyano Loyola, Faifer & Forte 2010) or quartic dependences (Blakeslee, Cantielo & Peng 2010). ( 2008) and, in the particular case of elliptical galaxies, in Chies-Santos et al. Evidence in this sense can be found, for example, in Norris et al. Under the common assumption of old ages, GC integrated colours should be dominated by chemical abundance (and in a secondary way by age). 2012), a key issue remains as an open subject: the connection between the GC abundances and their integrated colours. Important aspects, that eventually deal with large-scale properties of galaxies (see, for example Forte, Vega & Faifer 2012, and references therein) are both the age and chemical abundance distribution of these clusters.Įven though the quality and volume of chemical abundance () data for GCs is steadily growing (Alves-Brito et al. A thorough review of several issues in this context is presented, for example, in Brodie & Strader ( 2006). However, a unique integrating picture of that history, beyond some tentative approaches, is still missing. Globular clusters (GCs) are tracers of early events in the star-forming history in galaxies. Galaxies: haloes, galaxies: star clusters: general 1 INTRODUCTION On the other side, each (‘blue’ and ‘red’) GC subpopulation follows a distinct colour–colour relation. 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). This is accomplished by modelling the 10 GC colour histograms that can be defined in terms of the Cgriz ′ bands. The resulting multicolour colour–chemical abundance relations are used to test GC chemical abundance distributions. 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. We also present new ( C − T 1) 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). All these objects have previously published ( C − T 1) photometry. We present Gemini griz ′ photometry for 521 globular cluster (GC) candidates in a 5.5 × 5.5 arcmin 2 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.
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