The inevitable youthfulness of known high-redshift radio galaxies
ArXiv astro-ph/9905333 (1999)
Abstract:
Radio galaxies can be seen out to very high redshifts, where in principle they can serve as probes of the early evolution of the Universe. Here we show that for any model of radio-galaxy evolution in which the luminosity decreases with time after an initial rapid increase (that is, essentially all reasonable models), all observable high-redshift radio-galaxies must be seen when the lobes are less than 10^7 years old. This means that high-redshift radio galaxies can be used as a high-time-resolution probe of evolution in the early Universe. Moreover, this result helps to explain many observed trends of radio-galaxy properties with redshift [(i) the `alignment effect' of optical emission along radio-jet axes, (ii) the increased distortion in radio structure, (iii) the decrease in physical sizes, (iv) the increase in radio depolarisation, and (v) the increase in dust emission] without needing to invoke explanations based on cosmology or strong evolution of the surrounding intergalactic medium with cosmic time, thereby avoiding conflict with current theories of structure formation.High-z radio galaxies and the 'youth-redshift degeneracy'
ASTR SOC P 193 (1999) 75-78
Abstract:
We discuss a unifying explanation for many 'trends with redshift' of radio galaxies which includes the relevance of their ages (time since their jet triggering event), and the marked dependence of their ages on redshift due to the selection effect of imposing a flux-limit. We briefly describe some important benefits which this 'youth-redshift degeneracy' brings.No evidence for a 'redshift cut-off' for the most powerful classical double radio sources
ASTR SOC P 193 (1999) 90-93
Abstract:
We use three samples (3CRR, 6CE and 6C*) to investigate the radio luminosity function (RLF) for the 'most powerful' low-frequency selected radio sources. We find that the data are well fitted by a model with a constant ca-moving space density at high redshift as well as by one with a declining co-moving space density above some particular redshift. This behaviour is very similar to that inferred for steep-spectrum radio quasars by Willott et al (1998) in Line with the expectations of Unified Schemes. We conclude that there is as yet no evidence for a 'redshift cutoff' in the co-moving space densities of powerful classical double radio sources, and rule out a art-off at z less than or similar to 2.5.The 7C Redshift Survey - understanding radio-loud quasars and radio galaxies
ASTR SOC P 162 (1999) 135-144
Abstract:
Orientation-based unified schemes for radio-loud quasars and radio galaxies are discussed in the light of a new complete sample of identified radio sources - the 7C Redshift Survey. Selected at the low radio frequency of 151 MHz this sample is free of orientation biases and together with the 3CRR sample allows a direct comparison of the properties of radio galaxies and quasars. The fraction of quasars in complete samples is used to estimate the opening angle of the putative obscuring torus. Correlations between the extended radio luminosity and the optical continuum and narrow emission line luminosities are presented and discussed in terms of the physical processes occurring in radio-loud AGN.The Nature and Evolution of Classical Double Radio Sources from Complete Samples
ArXiv astro-ph/9810197 (1998)