GAMA/WiggleZ: the 1.4 GHz radio luminosity functions of high- and low-excitation radio galaxies and their redshift evolution to z = 0.75

• Published in: Monthly notices of the Royal Astronomical Society 2016-07, Vol.460 (1), p.2-17
• Main Authors: Pracy, Michael B., Ching, John H. Y., Sadler, Elaine M., Croom, Scott M., Baldry, I. K., Bland-Hawthorn, Joss, Brough, S., Brown, M. J. I., Couch, Warrick J., Davis, Tamara M., Drinkwater, Michael J., Hopkins, A. M., Jarvis, M. J., Jelliffe, Ben, Jurek, Russell J., Loveday, J., Pimbblet, K. A., Prescott, M., Wisnioski, Emily, Woods, David
• Format: Article
• Language: English
• Subjects: Accretion disks; Active galactic nuclei; Comparative analysis; Evolution; Luminosity; Mathematical models; Radio; Radio galaxies; Red shift; Star & galaxy formation
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stw910

We present radio active galactic nuclei (AGN) luminosity functions over the redshift range 0.005 < z < 0.75. The sample from which the luminosity functions are constructed is an optical spectroscopic survey of radio galaxies, identified from matched Faint Images of the Radio Sky at Twenty-cm survey (FIRST) sources and Sloan Digital Sky Survey images. The radio AGN are separated into low-excitation radio galaxies (LERGs) and high-excitation radio galaxies (HERGs) using the optical spectra. We derive radio luminosity functions for LERGs and HERGs separately in the three redshift bins (0.005 < z < 0.3, 0.3 < z < 0.5 and 0.5 < z < 0.75). The radio luminosity functions can be well described by a double power law. Assuming this double power-law shape the LERG population displays little or no evolution over this redshift range evolving as ${\sim } (1+z)^{0.06^{+0.17}_{-0.18}}$ assuming pure density evolution or ${\sim } (1+z)^{0.46^{+0.22}_{-0.24}}$ assuming pure luminosity evolution. In contrast, the HERG population evolves more rapidly, best fitted by ${\sim } (1+z)^{2.93^{+0.46}_{-0.47}}$ assuming a double power-law shape and pure density evolution. If a pure luminosity model is assumed, the best-fitting HERG evolution is parametrized by ${\sim } (1+z)^{7.41^{+0.79}_{-1.33}}$ . The characteristic break in the radio luminosity function occurs at a significantly higher power (≳1 dex) for the HERG population in comparison to the LERGs. This is consistent with the two populations representing fundamentally different accretion modes.