Structural parameters for globular clusters in NGC 5128. III. ACS surface-brightness profiles and model fits

TL;DR

This study analyzes the surface-brightness profiles of 131 globular clusters in NGC 5128 using HST/ACS imaging, fitting models to derive structural parameters and predicting velocity dispersions, thereby enhancing understanding of their properties.

Contribution

It provides a comprehensive catalog of structural and dynamical parameters for GCs in NGC 5128 using model fits to surface-brightness profiles, extending previous data and comparing models.

Findings

Most GCs are well fit by isotropic Wilson models.

Predicted velocity dispersions agree with available spectroscopic data.

Majority of clusters have more extended envelopes than King models.

Abstract

We present internal surface-brightness profiles, based on HST/ACS imaging in the F606W bandpass, for 131 globular cluster (GC) candidates with luminosities 10^4 - 3 x 10^6 solar, in the giant elliptical galaxy NGC 5128. Several structural models are fit to the profile of each cluster and combined with mass-to-light ratios from population-synthesis models, to derive a catalogue of fundamental structural and dynamical parameters parallel in form to the catalogues recently produced by McLaughlin & van der Marel and Barmby et al. for GCs and massive young star clusters in Local Group galaxies. As part of this, we provide corrected and extended parameter estimates for another 18 clusters in NGC 5128, which we observed previously. We show that, like GCs in the Milky Way and some of its satellites, the majority of globulars in NGC 5128 are well fit by isotropic Wilson models, which have intrinsically more distended envelope structures than the standard King lowered isothermal spheres. We use our models to predict internal velocity dispersions for every cluster in our sample. These predictions agree well in general with the observed dispersions in a small number of clusters for which spectroscopic data are available. In a subsequent paper, we use these results to investigate scaling relations for GCs in NGC 5128.