Astron. Astrophys. 348, 418-436 (1999)

Globular clusters in NGC 5128 ^*

S. Holland ¹, P. Côté ^{**  2} and J.E. Hesser <sup>3

1</sup> Institut for Fysik og Astronomi (IFA), Aarhus Universitet, Ny Munkegade, Bygning 520, DK-8000 Århus C, Denmark (holland@obs.aau.dk)
² California Institute of Technology, Mail Stop 105-24, Pasadena, CA 91125, USA (pc@astro.caltech.edu)
³ Dominion Astrophysical Observatory, Herzberg Institute of Astrophysics, National Research Council, 5071 West Saanich Road, Victoria, B.C., V8X 4M6, Canada (Jim.Hesser@hia.nrc.ca)

Received 3 February 1999 / Accepted 21 May 1999

Abstract

We used the Wide Field Planetary Camera 2 aboard the Hubble Space Telescope to search for globular clusters in the inner regions of the nearby giant elliptical galaxy NGC 5128. This galaxy is believed to be the product of a merger between a large elliptical galaxy and a small late-type spiral between 160 and 500 Myr ago. We identified 21 globular cluster candidates and measured their core radii, tidal radii, half-mass radii, ellipticities, position angles, and colors. We find evidence that the NGC 5128 globular cluster candidates are systematically more elliptical than are those of the Milky Way. Approximately half of the candidates have colors that are consistent with their being either old, unreddened globular clusters, similar to those found in the Milky Way, or young, reddened globular clusters that may have formed during the recent merger event. Most of the rest have colors that are consistent with their being old globular clusters similar to those found in the Milky Way. We find one blue object with . The color, reddening, and integrated magnitude of this object are consistent with its being a small globular cluster with an age of Myr and a mass (based on its integrated luminosity) of . We find no evidence for bimodality in the colors of the globular cluster candidates in our sample beyond what can be explained by uncertainties in the differential reddening.

Key words: methods: data analysis galaxies: individual: NGC 5128 galaxies: peculiar galaxies: star clusters

* Based in observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.
** Sherman M. Fairchild Fellow

Send offprint requests to: S. Holland

SIMBAD Objects

Contents

• 1. Introduction
• 2. The data
  • 2.1. Observations
  • 2.2. Data reductions
    • 2.2.1. Identifying globular cluster candidates
    • 2.2.2. Fitting Michie-King models
  • 2.3. Contamination
  • 2.4. Uncertainties in the structural parameters
• 3. Structural parameters
  • 3.1. Core radii
  • 3.2. Tidal radii
  • 3.3. Half-mass radii
  • 3.4. Ellipticities
  • 3.5. Correlations of cluster properties with distance
• 4. Colors
  • 4.1. The photometry
  • 4.2. Reddening within NGC 5128
  • 4.3. Iron abundance
• 5. Young GCs in NGC 5128
• 6. Conclusions
• Acknowledgements
• References

© European Southern Observatory (ESO) 1999

Online publication: July 26, 1999
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