Journal Article

Mapping the galaxy NGC 4486 (M87) through its globular cluster system

Juan C. Forte, E. Irene Vega and Favio Faifer

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 421, issue 1, pages 635-650
Published in print March 2012 | ISSN: 0035-8711
Published online March 2012 | e-ISSN: 1365-2966 | DOI:
Mapping the galaxy NGC 4486 (M87) through its globular cluster system

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As shown in previous works, globular clusters (GCs) 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 (M87) by combining several data sources. The results show that GCs 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, ≈1.0(±0.3) × 10−9. The total stellar mass derived for NGC 4486 is 6.8(±1.1) × 1011 M with a baryonic mass fraction fb= 0.08(±0.01).

Keywords: globular clusters: general; galaxies: haloes; galaxies: star clusters: general

Journal Article.  10464 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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