Sizes of Confirmed Globular Clusters in NGC 5128: A Wide-Field High-Resolution Study

TL;DR

This study measures the sizes of confirmed globular clusters in NGC 5128, revealing that size differences between red and blue clusters are mainly due to projection effects and their spatial distribution within the galaxy.

Contribution

First comprehensive analysis of globular cluster sizes in NGC 5128 extending to large galactocentric distances using high-resolution imaging.

Findings

Red clusters are about 30% smaller than blue clusters within 1 R_eff.

Size difference diminishes with increasing galactocentric distance.

Size differences can be explained by projection effects and spatial distribution.

Abstract

Using Magellan/IMACS images covering a 1.2 x 1.2 sq. degree FOV with seeing of 0.4"-0.6", we have applied convolution techniques to analyse the light distribution of 364 confirmed globular cluster in the field of NGC 5128 and to obtain their structural parameters. Combining these parameters with existing Washington photometry from Harris et al. (2004), we are able to examine the size difference between metal-poor (blue) and metal-rich (red) globular clusters. For the first time, this can be addressed on a sample of confirmed clusters that extends to galactocentric distances about 8 times the effective radius, R$_{eff}$, of the galaxy. Within 1 R$_{eff}$, red clusters are about 30% smaller on average than blue clusters, in agreement with the vast majority of extragalactic globular cluster systems studied. As the galactocentric distance increases, however, this difference becomes negligible. Thus, our results indicate that the difference in the clusters' effective radii, r$_e$, could be explained purely by projection effects, with red clusters being more centrally concentrated than blue ones and an intrinsic r$_e$--R$_{gc}$ dependence, like the one observed for the Galaxy.