Giant Radio Galaxies

Giant radio galaxies (GRGs) are the largest structures associated with single galaxies. Their linear sizes exceed 1 Mpc and so they form the extreme tail of the radio galaxy population. Because they have expanded to such large sizes, GRGs are thought to be the endpoint of radio galaxy evolution and provide important constraints to evolutionary models. They extend well past the environment of their host galaxy and act as direct probes of the intergalactic medium. I have carried out a survey for giant radio galaxies from a subset of the Sydney University Molonglo Sky Survey (SUMSS). My search area covered approximately 2100 square degrees, which corresponds to 26% of the area to be surveyed by SUMSS, or 5% of the sky. This is the most comprehensive southern sky GRG survey to date. I have identified twelve confirmed giants, a space density of one per 175 square degrees, and seventeen other candidate giants. The properties of these sources agree with a similar study in the northern hemisphere, and are consistent with theoretical models of the evolution of radio galaxies. Some interesting sources were found including: several double-double radio galaxies which show evidence of recurrent nuclear activity; some sources that may be the faded remnants of old radio galaxies; and J0331-771, perhaps the second largest radio galaxy known. A detailed investigation of one very powerful giant radio galaxy, J1919-799, revealed the processes at work in radio galaxies.