Abstract:
The S -band Polarisation All Sky Survey (SPASS/ATCA) rotation measure (RM) catalogue is the largest broadband RM catalogue to
date, increasing the RM density in the sparse southern sky. Through analysis of this catalogue, we report a latitude dependency of the
Faraday complexity of polarised sources in this catalogue within 10◦ of the Galactic plane towards the inner Galaxy. In this study,
we aim to investigate this trend with follow-up observations using the Australia Telescope Compact Array (ATCA). We observe 95
polarised sources from the SPASS/ATCA RM catalogue at 1.1–3.1 GHz with ATCA’s 6 km configuration. We present Stokes QU
fitting results and a comparative analysis with the SPASS/ATCA catalogue. We find an overall decrease in complexity in these sources
with the higher angular resolution observations, with a complexity fraction of 42%, establishing that the majority of the complexity
in the SPASS/ATCA sample is due to the mixing-in of diffuse Galactic emission at scales θ > 2.8
0
. Furthermore, we find a correlation
between our observed small-scale complexity θ < 2.8
0
and the Galactic spiral arms, which we interpret to be due to Galactic turbulence
or small-scale polarised emission. These results emphasise the importance of considering the maximum angular scale to which the
observations are sensitive in the classification of Faraday complexity; the effect of which can be more carefully investigated with
SKA-precursor and pathfinder arrays (e.g. MeerKAT and ASKAP).
