WHAT DOES THE UNIVERSE LOOK LIKE THROUGH POLARISED SUNGLASSES? Measuring the Angular Clustering of the Polarised Sky Supervised by: Bryan Gaensler (University of Sydney) Ilana Feain (CSIRO) Adam Schaefer

Polarisation in radio galaxies originates in the lobe structures emanating from the nucleus. Fast moving electrons in a large, ordered magnetic field radiate synchrotron radiation which we detect and analyse with telescopes. Polarisation In The Sky

The Data The VLA is a radio antenna array consisting of 27x25m dishes with a separation of 1.3 km. The NVSS survey catalogued over 2 million points in the sky. Only of the most polarised of these objects were studied. The data was obtained from A R Taylor, J Stil and C Sunstrum ‘A rotation measure image of the sky’ (2009)

Calculating The Two Point Angular Correlation Function A Recipe for the correlation function: 1.Choose a galaxy and calculate the angular distance between it and every other galaxy. 2.Count how many objects lie between θ and θ+dθ 3.Repeat for every other galaxy in the data list 4.Repeat for a random data set θ θ+dθ Galaxies DD=Data-data separation RR=Random-random separation

DD=Data-data separation RR=Random-random separation DR=Data-random separation ( degrees )

Polarised sources All Sources The graphs of w(θ) for both polarised galaxies and total intensity show a similar shape. Right hand Graph from: Blake, C, Wall, J(2002) ‘Quantifying Angular Clustering In Wide Area Radio Surveys’ Monthly Proceedings of The Royal Astronomical Society, Vol. 337 p.997 Comparing Results (degrees)

Image from: Many radio galaxies exhibit multiple components in the radio part of the spectrum. Radio lobes are a product of magnetic fields around a central black hole forcing in-falling material into jets. These lobes are identified as two separate objects by the NVSS Small Angular Separations: Multiple Component Sources

Polarised sources All Sources Right hand Graph from: Blake, C, Wall, J(2002) ‘Quantifying Angular Clustering In Wide Area Radio Surveys’ Monthly Proceedings of The Royal Astronomical Society, Vol. 337 p.997 Comparing Results (degrees)

Sidelobes The low clustering is an artefact of the survey, not the clustering of radio galaxies. Noise around the NVSS main beam. Image from: Condon, J et al (1998) ‘The NRAO VLA Sky Survey’ The Astrophysical Journal, Vol. 115, p Instrumental Effects The NVSS suffered from diffraction patterns. Faint objects may have been lost in this part of the image and hence not catalogued.

Polarised sources All Sources Right hand Graph from: Blake, C, Wall, J(2002) ‘Quantifying Angular Clustering In Wide Area Radio Surveys’ Monthly Proceedings of The Royal Astronomical Society, Vol. 337 p.997 Large Scale Structure (degrees) Highly polarised sources are distributed evenly throughout the universe. It is possible that all radio galaxies may go through a period of high magnetic activity at some stage of their evolution.

Future Investigation and Conclusions The two point angular correlation function does not preserve information about the shape of the clustering in the data. Information about clustering along our line of sight is lost. A future study of the clustering of highly polarised sources might include the distances to the galaxies in question. Conclusions - A large fraction of highly polarised galaxies have radio lobes -The NVSS suffers from instrumental effects which makes estimating clustering on some angular scales difficult. -Highly polarised galaxies show little clustering on large scales.