Welcome to the new version of CaltechAUTHORS. Login is currently restricted to library staff. If you notice any issues, please email coda@library.caltech.edu
Published July 1, 1996 | Published
Journal Article Open

Detection of the Tip of the Red Giant Branch in NGC 5128


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 M_(bot) ~ -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.

Additional Information

© 1996 American Astronomical Society. Provided by the NASA Astrophysics Data System. Received 1995 October 30; accepted 1996 January 5. Based on observations with the NASA/ESA Hubble Space Telescope. We are grateful to Daya Rawson and Peter Stetson for contributing their expertise in photometry and Neill Reid for star count calculations. We thank Gary Da Costa and Carl Grillmair for critical reading of the manuscript and John Graham and Jay Frogel for their stimulating remarks and suggestions. This research was carried out by the WFPC2 Investigation Definition Team for JPL and was sponsored by NASA through contract NAS7-1260.

Attached Files

Published - 1996ApJ___465___79S.pdf


Files (6.2 MB)
Name Size Download all
6.2 MB Preview Download

Additional details

August 19, 2023
October 19, 2023