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

TL;DR

This study uses deep radio observations of 47 Tuc and Omega Centauri to search for intermediate-mass black holes, setting upper limits on their possible masses and discussing implications for IMBH presence in globular clusters.

Contribution

First deep radio continuum observations of these clusters to constrain the existence of intermediate-mass black holes using the fundamental plane relation.

Findings

No significant radio emission detected from cluster centers.

Upper limits on radio flux set constraints on IMBH masses.

Potential 2.5-sigma detections near centers suggest need for further observations.

Abstract

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.