Radio Continuum Observations of 47 Tucanae and Omega Centauri: Hints for Intermediate-mass Black Holes?

Ting-Ni Lu, Albert K. H. Kong

Published 2011-02-08Version 1

We present results of deep radio continuum observations of two galactic globular clusters 47 Tucanae (47 Tuc) and Omega Centauri (Omega Cen) with Australia Telescope Compact Array (ATCA). No statistically significant evidence for radio emission was found from the central region for the two clusters. However, both clusters show a 2.5-sigma detection near the center that may be confirmed by future deeper radio observations. The 3-sigma upper limits of the radio observations is 20 and 40 microJy/beam for Omega Cen and 47 Tuc, respectively. By using the fundamental plane of accreting black holes which describes the relationship between radio luminosity, X-ray luminosity and black hole mass, we constrain the mass of a possible intermediate-mass black hole (IMBH) in the globualar clusters. We also compare our results with other globular clusters and discuss the existence of IMBHs in globular clusters.