Browsing by Author "Forbes, DA"

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    Ages and metallicities of Hickson compact group galaxies
    (2004) Proctor, RN; Forbes, DA; Hau, GKT; Beasley, MA; De Silva, GM; Contreras, R; Terlevich, AI
    Hickson compact groups (HCGs) constitute an interesting extreme in the range of environments in which galaxies are located, as the space density of galaxies in these small groups are otherwise only found in the centres of much larger clusters. The work presented here uses Lick indices to make a comparison of ages and chemical compositions of galaxies in HCGs with those in other environments (clusters, loose groups and the field). The metallicity and relative abundance of 'alpha-elements' show strong correlations with galaxy age and central velocity dispersion, with similar trends found in all environments. However, we show that the previously reported correlation between a-element abundance ratios and velocity dispersion disappears when a full account is taken of the abundance ratio pattern in the calibration stars. This correlation is thus found to be an artefact of incomplete calibration to the Lick system.
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    Imaging of the merging galaxy NGC 3597 and its population of protoglobular clusters
    (2000) Forbes, DA; Hau, GKT
    We present wide field-of-view near-infrared imaging from the NTT and very deep optical imaging from the HST of the young merging galaxy NGC 3597. The morphology of the galaxy and the properties of the newly formed protoglobular clusters (PGCs) are examined. Our K-band data reveal the presence of a second nucleus, which provides further evidence that NGC 3597 is the result of a recent merger. Combining new K-band photometry with optical photometry, we are able for the first time to derive a unique age for the newly formed PGCs of a few Myr. This is consistent with the galaxy starburst age of less than or equal to 10 Myr. From deep HST imaging, we are able to probe the luminosity function similar to 8 magnitudes fainter than normal, old globular clusters, and confirm that the PGCs have a power-law distribution with a slope of similar to-2.