The AIMSS Project - III. The stellar populations of compact stellar systems

JANZ, J.; NORRIS, M.; FORBES, D.; HUXOR, A.; ROMANOWSKY, A.; FRANK, M.; ESCUDERO, C. G.; FAIFER, F. R.; FORTE, J. C.; KANNAPPAN, S.; MARASTON, C.; BRODIE, J.; STRADER; THOMPSON, B.

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2016 vol. 456 p. 617 - 632

0035-8711

In recent years, a growing zoo of compact stellar systems (CSSs) havebeen found whose physical properties (mass, size, velocity dispersion)place them between classical globular clusters (GCs) and true galaxies,leading to debates about their nature. Here we present results using aso far underutilized discriminant, their stellar population properties.Based on new spectroscopy from 8-10m telescopes, we derive ages,metallicities, and [α/Fe] of 29 CSSs. These range from GCs withsizes of merely a few parsec to compact ellipticals (cEs) larger thanM32. Together with a literature compilation, this provides a panoramicview of the stellar population characteristics of early-type systems. Wefind that the CSSs are predominantly more metal rich than typicalgalaxies at the same stellar mass. At high mass, the cEs depart from themass-metallicity relation of massive early-type galaxies, which forms acontinuous sequence with dwarf galaxies. At lower mass, the metallicitydistribution of ultracompact dwarfs (UCDs) changes at a few times107 M⊙, which roughly coincides with the masswhere luminosity function arguments previously suggested the GCpopulation ends. The highest metallicities in CSSs are paralleled onlyby those of dwarf galaxy nuclei and the central parts of massive earlytypes. These findings can be interpreted as CSSs previously being moremassive and undergoing tidal interactions to obtain their current massand compact size. Such an interpretation is supported by CSSs withdirect evidence for tidal stripping, and by an examination of the CSSinternal escape velocities.