Structural Parameters for Globular Clusters in NGC 5128
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abstract
We present new imaging measurements of 27 individual globular clusters in the
halo of the nearby elliptical galaxy NGC 5128, obtained with the Hubble Space
Telescope STIS and WFPC2 cameras. Combining these with similar data for
selected inner-halo clusters from Holland et al. 1999 (AAp, 348, 418), we now
have a total sample of 43 NGC 5128 globular clusters with measured structural
properties. Classic King-model profiles match the clusters extremely well, and
their core- and half-light radii, central surface brightness, and central
concentration fall in very much the same range as do the clusters in the Milky
Way and M31. We find half a dozen bright clusters which show tentative evidence
for light that extends beyond the nominal tidal radius, or possibly ones in
which anisotropic velocity distributions are important. We also confirm
previous indications that NGC 5128 contains relatively more clusters with large
(> 0.2) ellipticity than does the Milky Way. Finally, calculations of the
cluster binding energies E_b as defined by McLaughlin 2000 (ApJ, 539,618) show
that the NGC 5128 clusters occupy the same extremely narrow region of the
parametric ``fundamental plane'' as do their Milky Way counterparts. Our data
are thus strongly consistent with the claim that the globular clusters in both
NGC 5128 and the Milky Way are fundamentally the same type of object: old star
clusters with similar mass-to-light ratios and King-model structures.
