Oral Presentation Astronomical Society of Australia Annual Scientific Meeting including HWWS 2013

Do All Galaxies' Globular Clusters Have the Same Stellar Populations? (#72)

Christopher Usher 1 , The SLUGGS Survey
  1. Swinburne University of Technology, Hawthorn, VIC, Australia
Optical colours are typical used to infer the metallicities of extragalactic globular clusters. However the form of the colour-metallicity relation has been a matter of debate. As part of the SLUGGS survey of nearby early-type galaxies and their globular cluster systems we have used the DEIMOS multi-object spectrograph on Keck to obtain spectra of thousands of globular clusters. Previously we have used the strength of the near infrared calcium triplet to derive metallicities showing that galaxies’ globular cluster metallicity distributions are bimodal like their globular cluster colour distributions. However we see evidence that different galaxies have different globular cluster colour-metallicity relations. Different colour-metallicity relations would imply that globular clusters in different galaxies have different ages, chemical abundances or stellar mass functions. We have now stacked our spectra by colour within each galaxy to allow us to measure the strength of weaker metal lines allowing us to confirm our CaT metallicities. By empirically comparing line ratios we can identify how globular clusters differ between galaxies.