Bibcode
Beasley, Michael A.; Bridges, Terry; Peng, Eric; Harris, William E.; Harris, Gretchen L. H.; Forbes, Duncan A.; Mackie, Glen
Bibliographical reference
Monthly Notices of the Royal Astronomical Society, Volume 386, Issue 3, pp. 1443-1463.
Advertised on:
5
2008
Citations
94
Refereed citations
93
Description
We have performed a spectroscopic study of globular clusters (GCs) in
the nearest giant elliptical NGC 5128 using the 2dF facility at the
Anglo-Australian Telescope. We obtained integrated optical spectra for a
total of 254 GCs, 79 of which are newly confirmed on the basis of their
radial velocities and spectra. In addition, we obtained an integrated
spectrum of the galaxy starlight along the southern major axis. We
derive an empirical metallicity distribution function (MDF) for 207 GCs
(~14 per cent of the estimated total GC system) based upon Milky Way
GCs. This MDF is multimodal at high statistical significance with peaks
at [Z/H] ~ -1.3 and -0.5. A comparison between the GC MDF and that of
the stellar halo at 20 kpc (~4Re) reveals close coincidence
at the metal-rich ends of the distributions. However, an inner 8-kpc
stellar MDF shows a clear excess of metal-rich stars when compared to
the GCs. We compare a higher signal-to-noise ratio (S/N) subsample (147
GCs) with two stellar population models which include non-solar
abundance ratio corrections. The vast majority of our sample (~90 per
cent) appears old, with ages similar to the Milky Way GC system. There
is evidence for a population of intermediate-age (~4-8 Gyr) GCs (<=15
per cent of the sample) which are on average more metal-rich than the
old GCs. We also identify at least one younger cluster (~1-2 Gyr) in the
central regions of the galaxy. Our observations are consistent with a
picture where NGC 5128 has undergone at least two mergers and/or
interactions involving star formation and limited GC formation since z =
1, however the effect of non-canonical hot stellar populations on the
integrated spectra of GCs remains an outstanding uncertainty in our GC
age estimates.
Related projects
Traces of Galaxy Formation: Stellar populations, Dynamics and Morphology
We are a large, diverse, and very active research group aiming to provide a comprehensive picture for the formation of galaxies in the Universe. Rooted in detailed stellar population analysis, we are constantly exploring and developing new tools and ideas to understand how galaxies came to be what we now observe.
Ignacio
Martín Navarro