SCYON Abstract

Received on May 15 2009

Globular cluster systems in nearby dwarf galaxies - II. Nuclear star clusters and their relation to massive Galactic globular clusters

AuthorsIskren Y. Georgiev (1), Michael Hilker (2), Thomas H. Puzia (3), Paul Goudfrooij (4), and Holger Baumgardt (1)
Affiliation(1) AIfA, Bonn, Germany
(2) ESO, Garching, Germany
(3) HIA, Victoria, Canada
(4) STScI, Baltimore, USA
Accepted byMonthly Notices of the Royal Astronomical Society
Contactiskren@astro.uni-bonn.de
URLhttp://de.arxiv.org/abs/0903.2857
Links

Abstract

Using luminosities and structural parameters of globular clusters (GCs) in the nuclear regions (nGCs) of low-mass dwarf galaxies from HST/ACS imaging we derive the present-day escape velocities (vesc) of stellar ejecta to reach the cluster tidal radius and compare them with those of Galactic GCs with extended (hot) horizontal branches (EHBs-GCs). For EHB-GCs, we find a correlation between the present-day vesc and their metallicity as well as (V-I)0 colour. The similar vesc, (V-I)0 distribution of nGCs and EHB-GCs implies that nGCs could also have complex stellar populations. The vesc-[Fe/H] relation could reflect the known relation of increasing stellar wind velocity with metallicity, which in turn could explain why more metal-poor clusters typically show more peculiarities in their stellar population than more metal-rich clusters of the same mass do. Thus the cluster vesc can be used as parameter to describe the degree of self-enrichment. The nGCs populate the same Mv vs. rh region as EHB-GCs, although they do not reach the sizes of the largest EHB-GCs like wCen and NGC 2419. We argue that during accretion the rh of an nGC could increase due to significant mass loss in the cluster vicinity and the resulting drop in the external potential in the core once the dwarf galaxy dissolves. Our results support the scenario in which Galactic EHB-GCs have originated in the centres of pre-Galactic building blocks or dwarf galaxies that were later accreted by the Milky Way.