Radio galaxies in the 2SLAQ Luminous Red Galaxy Survey - I: The evolution of low-power radio galaxies to z ~ 0.7

Elaine M. Sadler, Russell D. Cannon, Tom Mauch, Paul J. Hancock, David A. Wake, Nicholas P. Ross, Scott M. Croom, Michael J. Drinkwater, Alastair C. Edge, Daniel Eisenstein, Andrew M. Hopkins, Helen M. Johnston, Robert Nichol, Kevin A. Pimbblet, Roberto De Propris, Isaac G. Roseboom, Donald P. Schneider, Tom Shanks

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We have combined optical data from the 2dF-SDSS (Sloan Digital Sky Survey) LRG (Luminous Red Galaxy) and QSO (quasi-stellar object) (2SLAQ) redshift survey with radio measurements from the 1.4 GHz VLA (Very Large Array) FIRST (Faint Images of the Radio Sky at Twenty-cm) and NVSS (NRAO VLA Sky Survey) surveys to identify a volume-limited sample of 391 radio galaxies at redshift 0.4 < z < 0.7. By determining an accurate radio luminosity function for luminous early-type galaxies in this redshift range, we can investigate the cosmic evolution of the radio-galaxy population over a wide range in radio luminosity.
The low-power radio galaxies in our LRG sample (those with 1.4 GHz radio luminosities in the range 1024 to 1025 W Hz−1, corresponding to Fanaroff–Riley I (FR I) radio galaxies in the local Universe) undergo significant cosmic evolution over the redshift range 0 < z < 0.7, consistent with pure luminosity evolution of the form (1 +z)k, where k= 2.0 ± 0.3. Our results appear to rule out (at the 6–7σ level) models in which low-power radio galaxies undergo no cosmic evolution. The most powerful radio galaxies in our sample (with radio luminosities above 1026 W Hz−1) may undergo more rapid evolution over the same redshift range.
The evolution seen in the low-power radio-galaxy population implies that the total energy input into massive early-type galaxies from active galactic nucleus (AGN) heating increases with redshift, and was at least 50 per cent higher at z∼ 0.55 (the median redshift of the 2SLAQ LRG sample) than in the local universe.
Original languageEnglish
Pages (from-to)211-227
JournalMonthly Notices of the Royal Astronomical Society
Issue number1
Early online date11 Oct 2007
Publication statusPublished - 2007


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