Globular clusters in NGC 5128

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 V - I 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 {(V - I)}_0 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 {(V - I)}_0 < 0.26 +/- 0.09. The color, reddening, and integrated magnitude of this object are consistent with its being a small globular cluster with an age of phantom {0}im 100 Myr and a mass (based on its integrated luminosity) of <= 4000 M_sun. 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. Based in observations with the NASA/ESA {\it 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.