A Cyberinfrastructure platform to meet the needs of data intensive radio astronomy on route to the SKA

Radio sources with ultra-high polarisation

A sample of 129 unresolved radio sources with ultra-high linear polarisation (>30 per cent) has been selected from the NVSS (NRAO VLA Sky Survey). Such high average linear polarisation is unusual in extragalactic sources. Higher resolution ATCA (Australia Telescope Compact Array) and VLA (Very Large Array) observations confirm the high average polarisation but find that most of these sources are extended. SDSS (Sloan Digital Sky Survey) spectroscopy, where available, shows that the optical counterparts are elliptical galaxies with no detectable emission lines. The optical spectra, radio luminosity, linear size and spectral index of these sources are typical of radio-loud AGNs. Galaxy counts within a 1 Mpc radius of the radio sources show that these highly polarised sources are in environments similar to their low polarisation (<2 per cent) counterparts. Similarly the line-of-sight environments of the ultra-high polarisation sources are on average indistinguishable from those of the low polarisation sources. We conclude that the extraordinarily high average polarisation must be due to intrinsic properties of the sources, such as an extremely ordered source magnetic field, low internal thermal plasma density or the source magnetic field is preferentially oriented in the plane of the sky.