Spectropolarimetry with the Giant Metrewave Radio Telescope at 610 MHz: a case study of two southern compact group fields

Abstract

We present 610 MHz spectropolarimetric images from the Giant Metrewave Radio Telescope (GMRT). We discuss the properties of the GMRT's full-polarisation mode in detail and provide a technical characterisation of the instrument's polarisation performance. We show that the telescope can be used for wide-field spectropolarimetry. The application of Rotation Measure Synthesis results in a sensitivity at the level of tens of micro-Jy in Faraday space. As a demonstration of the instrument's capabilities, we present observations of two Southern Compact Groups - the Grus Quartet and USCG S063. The observations are compared with other radio and infra-red data to constrain the group members' spectral index, polarisation fraction, and Faraday depth. Radio continuum emission is detected from all four galaxies in the Grus Quartet and one galaxy in USCG S063. Linear polarisation is detected from a circumnuclear starburst ring in NGC 7552, the active nucleus of NGC 7582, and three extended radio galaxies in the background of the Grus Quartet field. These background sources allow for the classification of an FR-I and an X-shaped radio galaxy. No evidence is found for interaction with the intragroup medium in either galaxy group.