Abstract
This paper presents a new grid-based method for investigating the
evolution of the steep-spectrum radio luminosity function, with the aim
of quantifying the high-redshift cut-off suggested by previous work. To
achieve this, the Combined EIS-NVSS Survey of Radio Sources (CENSORS)
has been developed; this is a 1.4-GHz radio survey, containing 135
sources complete to a flux density of 7.2 mJy, selected from the NRAO
VLA Sky Survey (NVSS) over 6 deg2 of the ESO Imaging Survey
(EIS) Patch D. The sample is currently 73 per cent spectroscopically
complete, with the remaining redshifts estimated via the K-z or I-z
magnitude-redshift relation. CENSORS is combined with additional radio
data from the Parkes All-Sky, Parkes Selected Regions, Hercules and Very
Large Array (VLA) COSMOS samples to provide comprehensive coverage of
the radio power versus redshift plane. The redshift distributions of
these samples, together with radio source count determinations, and
measurements of the local luminosity function, provide the input to the
fitting process.
The modelling reveals clear declines, at >3σ significance, in
comoving density at z > 0.7 for lower luminosity sources (log P =
25-26); these turnovers are still present at log P > 27, but move to
z ≳ 3, suggesting a luminosity-dependent evolution of the redshift
turnover, similar to the 'cosmic downsizing' seen for other active
galactic nucleus populations. These results are shown to be robust to
the estimated redshift errors and to increases in the spectral index for
the highest redshift sources.
Analytic fits to the best-fitting steep spectrum grid are provided so
that the results presented here can be easily accessed by the reader, as
well as allowing plausible extrapolations outside of the regions covered
by the input data sets.
Original language | English |
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Pages (from-to) | 1900-1915 |
Number of pages | 16 |
Journal | Monthly Notices of the Royal Astronomical Society |
Volume | 416 |
Issue number | 3 |
DOIs | |
Publication status | Published - 21 Sep 2011 |
Keywords
- galaxies: active
- galaxies: evolution
- galaxies: high-redshift
- galaxies: luminosity function, mass function
- ACTIVE GALACTIC NUCLEI
- DIGITAL-SKY-SURVEY
- VLA-COSMOS SURVEY
- EIS-NVSS SURVEY
- PARKES SELECTED REGIONS
- STAR-FORMING GALAXIES
- LBDS-HERCULES SAMPLE
- K-Z RELATION
- 1.4 GHZ
- SPACE DENSITY