The luminosity-dependent high-redshift turnover in the steep spectrum radio luminosity function: clear evidence for downsizing in the radio-AGN population

摘要: This paper presents a new grid-based method for investigating the evolution of steep-spectrum radio luminosity function, with aim quantifying high-redshift cut-off suggested by previous work. To achieve this, Combined EIS–NVSS Survey Radio Sources (CENSORS) has been developed; this is 1.4-GHz survey, containing 135 sources complete to flux density 7.2 mJy, selected from NRAO VLA Sky (NVSS) over 6 deg2 ESO Imaging (EIS) Patch D. The sample currently 73 per cent spectroscopically complete, remaining redshifts estimated via the K–z or I–z magnitude–redshift relation. CENSORS combined additional data Parkes All-Sky, Selected Regions, Hercules and Very Large Array (VLA) COSMOS samples provide comprehensive coverage power versus redshift plane. distributions these samples, together source count determinations, measurements local input fitting process. The modelling reveals clear declines, at >3σ significance, in comoving at z > 0.7 lower (log P = 25–26); turnovers are still present log P > 27, but move to z ≳ 3, suggesting luminosity-dependent turnover, similar ‘cosmic downsizing’ seen other active galactic nucleus populations. These results shown be robust errors increases spectral index highest sources. Analytic fits best-fitting steep spectrum grid provided so that presented here can easily accessed reader, as well allowing plausible extrapolations outside regions covered sets.