Detection of the tip of the red giant branch in NGC 5128

Roberto Soria, Jeremy R. Mould, Alan M. Watson, John S. Gallagher, Gilda E. Ballester, Christopher J. Burrows, John T. Clarke, David Crisp, Richard E. Griffiths, J. Jeff Hester, John G. Hoessel, Jon A. Holtzman, Paul A. Scowen, Karl R. Stapelfeldt, John T. Trauger, James A. Westphal

Research output: Contribution to journalArticlepeer-review

88 Scopus citations


We present a color-magnitude diagram of more than 10,000 stars in the halo of the galaxy NGC 5128 (Centaurus A), based on WFPC2 images through V-band and I-band filters. The position of the red giant branch (RGB) stars is compared with the loci of the red giant branch in six well-studied globular clusters and in the dwarf elliptical galaxy NGC 185; the tip of the RGB is signalled by an observed turn-up in the luminosity function at I ≃ 24.1 ± 0.1 mag; this yields a distance modulus (m - M)0 = 27.8 ± 0.2 for NGC 5128 (i.e., a distance of 3.6 ± 0.2 Mpc), in agreement with previous determinations based on the planetary nebulae luminosity function and on the surface brightness fluctuations technique. The presence of an intermediate-age stellar population (∼5 Gyr) is suggested by the luminosity function of the asymptotic giant branch stars, extending up to I = 22.6 mag (for V - I > 2) and Mbol ∼ -5 mag; however, the number of these stars constrains the intermediate-age stellar population in the halo of NGC 5128 to be less than ∼10% of the total. The color distribution at constant I magnitude, albeit affected by the completeness level of our sample, strongly suggests a mean value of [Fe/H] > -0.9 dex, possibly similar to the value found in M31 and higher than that observed in NGC 185. Like the M31 halo, the halo of NGC 5128 exhibits a broad range of levels of chemical enrichment.

Original languageEnglish (US)
Pages (from-to)79-90
Number of pages12
JournalAstrophysical Journal
Issue number1 PART I
StatePublished - 1996
Externally publishedYes


  • Galaxies: Distances and redshifts
  • Galaxies: Individual (ngc 5128)
  • Galaxies: Stellar content
  • Russell diagram
  • Stars: Hertzsprung

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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