The outer halo of the nearest giant elliptical: a VLT/VIMOS survey of the resolved stellar populations in Centaurus A to 85 kpc

D. Crnojević, A. M. N. Ferguson, M. J. Irwin, E. J. Bernard, N. Arimoto, P. Jablonka, C. Kobayashi

Research output: Contribution to journalArticlepeer-review

Abstract

We present the first survey of resolved stellar populations in the remote outer halo of our nearest giant elliptical (gE), Centaurus A (D = 3.8 Mpc). Using the VIsible Multi Object Spectrograph (VIMOS)/Very Large Telescope (VLT) optical camera, we obtained deep photometry for four fields along the major and minor axes at projected elliptical radii of ˜30-85 kpc (corresponding to ˜5-14Reff). We use resolved star counts to map the spatial and colour distribution of red giant branch (RGB) stars down to ˜2 mag below the RGB tip. We detect an extended halo out to the furthermost elliptical radius probed (˜85 kpc or ˜14Reff), demonstrating the vast extent of this system. We detect a localized substructure in these parts, visible in both (old) RGB and (intermediate-age) luminous asymptotic giant branch stars, and there is some evidence that the outer halo becomes more elliptical and has a shallower surface brightness profile. We derive photometric metallicity distribution functions for halo RGB stars and find relatively high median metallicity values (med ˜ -0.9 to -1.0 dex) that change very little with radius over the extent of our survey. Radial metallicity gradients are measured to be ≈ -0.002-0.004 dex kpc-1, and the fraction of metal-poor stars (defined as [Fe/H] <-1.0) is ≈40-50 per cent at all radii. We discuss these findings in the context of galaxy formation models for the buildup of gE haloes.
Original languageEnglish
Pages (from-to)832-847
Number of pages16
JournalMonthly Notices of the Royal Astronomical Society
Volume432
Issue number1
DOIs
Publication statusPublished - Jun 2013

Keywords

  • galaxies: evolution
  • galaxies: individual: Cen A
  • galaxies: photometry
  • galaxies: stellar content
  • EARLY-TYPE GALAXIES
  • GLOBULAR-CLUSTER SYSTEM
  • NGC 5128 CENTAURUS
  • LARGE GALACTOCENTRIC RADII
  • HUBBLE-SPACE-TELESCOPE
  • METALLICITY DISTRIBUTION
  • SIZE EVOLUTION
  • PHOTOMETRIC PROPERTIES
  • FORMATION HISTORY
  • STAR-FORMATION

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