[92.15] Deep ACS imaging of the halo of Centaurus A

AAS 205th Meeting, 9-13 January 2005
Session 92 Ellipticals and Early Types
Poster, Wednesday, January 12, 2005, 9:20am-6:30pm, Exhibit Hall

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[92.15] Deep ACS imaging of the halo of Centaurus A

M. Rejkuba (ESO, Garching, Germany), L. Greggio (INAF, Padova, Italy), W. E. Harris (McMaster Univ., Hamilton, Canada), G. L. H. Harris (University of Waterloo, Waterloo, Canada), E. W. Peng (HIA/DAO, Victoria, Canada)

NGC 5128 (=Centaurus A) is the nearest easily observable giant elliptical galaxy, and thus it represents a unique testing ground for stellar population models. Previous WFPC2 photometry of its halo red-giant stars has shown that they are predominantly metal-rich ([M/H] ~-0.45 dex; Harris & Harris 2000, AJ 119, 2423), but very little is yet known about their spread in ages.

Using the Wide Field Camera (WFC) of the Advanced Camera for Survey (ACS) instrument at the Hubble Space Telescope we have obtained very deep photometry of a distant halo filed in NGC 5128, lying ~38 kpc south from the center. Our photometry reaches ~30 mag in V-band and reveals for the first time the red clump and asymptotic giant branch bump features in a giant elliptical galaxy. Constraining the metallicity from the colors of upper red giant branch stars, we explore the ages of the stars present in this remote halo field of NGC 5128, gaining the first quantitative information on its age distribution. This dataset is unique for any giant elliptical galaxy and will provide major new input to population synthesis techniques for such galaxies.

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