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

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Abstract

We present the first deep survey of resolved stellar populations in the remote outer halo of our nearest giant elliptical (gE), Centaurus A (D=3.8 Mpc). Using the VIMOS/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 ~5-14 R_{eff}). We use resolved star counts to map the spatial and colour distribution of red giant branch (RGB) stars down to ~2 magnitudes below the RGB tip. We detect an extended halo out to the furthermost elliptical radius probed (~85 kpc or ~14 R_{eff}), demonstrating the vast extent of this system. We detect a localised 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 ([Fe/H]_{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 to -0.004 dex/kpc and the fraction of metal-poor stars (defined as [Fe/H]
Original languageEnglish
Pages (from-to)832-847
Number of pages16
JournalMonthly Notices of the Royal Astronomical Society
Volume432
Issue number1
Early online date22 Apr 2013
DOIs
Publication statusPublished - 11 Jun 2013

Keywords

  • astro-ph.CO

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