Mapping the galaxy NGC 4486 (M87) through its Globular Cluster System

TL;DR

This study demonstrates that globular clusters effectively trace the structure, chemical composition, and mass distribution of galaxy NGC 4486 (M87), revealing detailed insights into its stellar populations and dark matter distribution.

Contribution

It provides a comprehensive analysis combining multiple data sources to map galaxy properties using globular clusters, extending previous assumptions about their role in galaxy structure.

Findings

Globular clusters trace surface brightness and color gradients up to 80.4 kpc.

The galaxy has a high metallicity bulge and a low metallicity halo with different shapes.

The distribution of blue GCs resembles dark matter distribution, with similar blue GC to dark mass ratios.

Abstract

As shown in previous works, globular clusters can be used to trace the overall structure of the diffuse stellar populations in early type galaxies if the number of clusters per unit stellar mass depends on metallicity. In this paper we further test this assumption in the galaxy NGC 4486 (M 87), by combining several data sources. The results show that globular clusters allow the mapping of the galaxy in terms of the surface brightness profile, integrated colour gradient, chemical abundance, and mass to luminosity ratios up to 1000 arcsec (or 80.4 kpc) from its centre (i.e. some 10 effective radii). The analysis indicates the presence of a dominant high metallicity bulge associated with the red globulars, whose ellipticity increases outwards, and of a more flattened low metallicity halo connected with the blue globulars. The chemical abundance gradient of the composite stellar population is remarkably similar to that inferred from X ray observations of hot gas. The mass-metallicity spectrum of the stellar population can, in principle, be understood in terms of inhomogeneous enrichment models. In turn, the distribution of the bluest GCs, and lowest metallicity halo stars, has an intriguing similarity with that of dark matter, a feature shared with NGC 1399. Also, in these two galaxies, the number of blue GCs per dark mass unit is identical within the errors, \approx 1.0(\pm0.3) \times 10^{-9} . The total stellar mass derived for NGC 4486 is 6.8(\pm1.1) \times 10^{11} M\odot with a baryonic mass fraction fb = 0.08(\pm 0.01).