http://arxiv.org/abs/1708.03087
Following previous work, we further confirm that the cosmic evolution of steep spectrum radio-loud AGNs (Active Galactic Nuclei) can be reproduced by a simple combination of density evolution (DE) and luminosity evolution (LE). This mixture evolution scenario can naturally explain the luminosity-dependent evolution of radio-loud AGNs. Our models successfully fitted a large amount of data on radio luminosity functions (RLFs) of steep-spectrum sources and multi-frequency source counts. The modeling indicate that the DE slowly increase as $(1+z)^{0.3 \thicksim 1.3}$ out to $z \thicksim 0.8$, and then rapidly decreases as $(1+z)^{-6.8 \thicksim -5.7}$, while the LE rapidly increase as $(1+z)^{4.8}$ out to a higher redshift (at least $z>3.5$). We find a high redshift decline (i.e. redshift cut-off) in the number density of steep-spectrum radio sources, but we can not conclude whether such decline is sharp or shallow. We believe that whether a redshift cut-off occurs or not depends mainly on DE, while its steepness is decided by LE, which, however, can not be well constrained due to the lack of high redshift sample. Most intriguingly, according to our mixture evolution scenario, there appears to be no need for different evolution for the low- and high-power radio-loud AGNs. Both types of sources experience the same combined evolution of DE and LE.
Z. Yuan, J. Wang, M. Zhou, et. al.
Fri, 11 Aug 17
33/45
Comments: Accepted for publication in ApJ. 11 pages, 8 figures