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AGN Space Densities and the FR Dichotomy

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Extended double-lobe radio sources can be morphologically classified into two groups: Fanaroff-Riley (FR) type I sources have the highest surface brightness along the jets near the core and FR type II sources show the highest surface brightness at the lobe extremities, as well as more collimated jets. This work focuses on a comparison of the space densities of FRI and FRII sources at different epochs, with a particular focus on FRI sources. The Combined NVSS -FIRST Galaxy catalogue (CoNFIG), a sample of radio sources at 1.4 GHz, includes VLA observations, FRI /FRII morphology classifications, optical identifications and redshift estimates. The final catalogue consists of 858 sources over 4 samples (CoNFIG-1,2,3 and 4 with flux density limits of S_1.4GHz = 1.3,0.8,0.2 and 0.05 Jy respectively). It is 95.7% complete in radio morphology classification and 74.3% of the sources have redshift data. Combining CoNFIG with complementary samples, the distribution and cosmic evolution of FRI and FRII sources are investigated. It is found that FRI sources undergo mild evolution and that, at the same radio luminosity, FRI and FRII sources show similar space density enhancements in various redshift ranges, implying a common mechanism powering the luminosity-dependent evolution. This improved understanding of radio galaxy evolution will also give better insight into the physics of AGN and their role in galaxy formation.

This talk is part of the Cavendish Astrophysics Seminars series.

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