Speaker
Description
We report the largest study to date of the resolved Faraday rotation (RM) and depolarization across the lobes of double radio sources. Our work utilises the ongoing EMU and POSSUM surveys with ASKAP, which will cover half the sky. EMU produces broad-band Stokes I images and a source catalogue at 943 MHz. POSSUM performs RM synthesis on the same data, yielding RMs at each high-SNR pixel.
POSSUM will measure RMs for ~1 million sources with many thousands large enough to resolve details within each radio lobe. This allows us to check claims for systematic RM patterns such as the Laing-Garrington effect, which rest on only a few dozen objects, with poorer data than POSSUM will achieve for thousands. Pre-POSSUM results were usually explained in terms of the inclination of a source embedded in an atmosphere that dominates the Faraday depth, but this may be too simple.
As a prototype, we used a 0.05 sr region where RM maps and EMU catalogues have been made. We selected about 125 'islands' with solid angle > 6000 sq" above the 5-sigma Stokes I contour. Most represent a single source but some constitute one lobe of a double, while others are superpositions of unrelated objects. Selection by size yields a lower mean luminosity than by flux density- Fanaroff-Riley type I sources are common, typically found in groups/clusters. We present highlights from these maps, an analysis of a subset to see how much human quality control is needed, and a first look at statistical trends.
