The 6C** sample of steep-spectrum radio sources: II - Redshift distribution and the space density of high-redshift radio galaxies

Abstract

We use the 6C** sample to investigate the co-moving space density of powerful, steep-spectrum radio sources. This sample, consisting of 68 objects, has virtually complete K-band photometry and spectroscopic redshifts for 32 per cent of the sources. In order to find its complete redshift distribution, we develop a method of redshift estimation based on the K-z diagram of the 3CRR, 6CE, 6C* and 7CRS radio galaxies. Based on this method, we derive redshift probability density functions for all the optically identified sources in the 6C** sample. Using a combination of spectroscopic and estimated redshifts, we select the most radio luminous sources in the sample. Their redshift distribution is then compared with the predictions of the radio luminosity function of Jarvis et al. We find that, within the uncertainties associated with the estimation method, the data are consistent with a constant co-moving space density of steep-spectrum radio sources beyond z > 2.5, and rule out a steep decline.

arXiv comment17 pages including 11 figures and 4 tables. This replacement matches the published MNRAS version; revised with minor edits, corrections to table 1, fig. 5 and to references. Results and conclusions are unaffected

References in corpus (27)

• The broken hierarchy of galaxy formation
• A Survey of z>5.7 Quasars in the Sloan Digital Sky Survey II: Discovery of Three Additional Quasars at z>6
• Quasars, their host galaxies, and their central black holes
• The Nature and Evolution of Classical Double Radio Sources from Complete Samples
• The radio luminosity function from the low-frequency 3CRR, 6CE & 7CRS complete samples
• Near-infrared imaging and the K-z relation for radio galaxies in the 7C Redshift Survey
• A Radio Galaxy at z=5.19
• Optical and Near-IR Imaging of Ultra Steep Spectrum Radio Sources - The K-z diagram of radio and optically selected galaxies
• The relationship between radio luminosity and black-hole mass in optically-selected quasars
• A sample of 6C radio sources designed to find objects at redshift > 4: III --- imaging and the radio galaxy K-z relation
• A first sample of faint radio sources with virtually complete redshifts: I. Infrared images, the Hubble diagram, and the alignment effect
• A sample of radio galaxies spanning three decades in radio luminosity - I. The host-galaxy properties and black-hole masses
• The inevitable youthfulness of known high-redshift radio galaxies
• Spectroscopy of Ultra Steep Spectrum Radio Sources
• A sample of 6C radio sources with virtually complete redshifts. II - optical spectroscopy
• A sample of 6C radio sources designed to find objects at redshift > 4: II --- spectrophotometry and emission line properties
• A submillimetre difference between radio galaxies and radio quasars: evidence for quasar-heated dust and synchronized submillimetre and radio source activity
• On the redshift cut-off for flat-spectrum radio sources
• On the redshift cut-off for steep-spectrum radio sources
• A sample of 6C radio sources designed to find objects at redshift > 4: the radio data
• Lyman Break Galaxies at z = 4 - 6 in cosmological SPH Simulations
• Massive Ellipticals at High Redshift: NICMOS Imaging of Z~1 Radio Galaxies
• The Evolution of the Stellar Hosts of Radio Galaxies
• The hyperluminous infrared quasar 3C 318 and its implications for interpreting sub-mm detections of high-redshift radio galaxies
• Optical spectroscopy of radio galaxies in the 7C Redshift Survey
• The 6C** sample of steep-spectrum radio sources: I - Radio data, near-infrared imaging and optical spectroscopy
• The discovery of a type-II quasar at z = 1.65 with integral-field spectroscopy

Cited by in corpus (20)

• EMU: Evolutionary Map of the Universe
• Radio and Millimeter Continuum Surveys and their Astrophysical Implications
• Radio imaging of the Subaru/XMM-Newton Deep Field - III. Evolution of the radio luminosity function beyond z=1
• A model for the cosmological evolution of low frequency radio sources
• A Combined EIS-NVSS Survey Of Radio Sources (CENSORS) III: Spectroscopic observations
• New Insights on the z-alpha Correlation from Complete Radio Samples
• The discovery of a typical radio galaxy at z = 4.88
• Forecasts for Dark Energy Measurements with Future HI Surveys
• Deep GMRT 150 MHz observations of the LBDS-Lynx region: Ultra-Steep Spectrum Radio Sources
• LOFAR low-band antenna observations of the 3C295 and Bootes fields: source counts and ultra-steep spectrum sources
• Low-power radio galaxy environments in the Subaru/XMM-Newton Deep Field at z~0.5
• Imaging and Spectroscopy of Ultra Steep Spectrum Radio Sources
• On the Evolution of the Cores of Radio Sources and Their Extended Radio Emission
• A new sample of southern radio galaxies: Host galaxy masses and star-formation rates
• A mixture evolution scenario of the AGN radio luminosity function. II. Do low- and high-power radio-loud AGNs evolve differently?
• The evolution of radio sources in the UKIDSS-DXS XMM-LSS field
• A mixture evolution scenario of the AGN radio luminosity function
• Effect of spectral index distribution on estimating the AGN radio luminosity function
• Radio Astronomy in LSST Era
• The FIRST radio survey: The K-z diagram of FIRST radio sources identified in the Boötes and Cetus fields