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2002AJ....124.1239H - Astron. J., 124, 1239-1257 (2002/September-0)

A study of 3CR radio galaxies from z=0.15 to z=0.65. II. Evidence for an evolving radio structure.

HARVANEK M. and STOCKE J.T.

Abstract (from CDS):

Radio morphology data have been collected for a sample of radio galaxies from the Revised Third Cambridge Catalog in the redshift range 0.15<z<0.65. Radio structure parameters including largest physical size, projected bending angle (β), lobe length asymmetry (Q), and hot spot placement (Fanaroff-Riley ratio) have been measured from the highest-quality radio maps available. Combined with similar data for quasars in the same redshift range, these morphology data are used in conjunction with a quantification of the richness of the cluster environment around these objects (the amplitude of the galaxy-galaxy spatial covariance function, Bgg) to search for indirect evidence of a dense intracluster medium (ICM). This is accomplished by searching for confinement and distortions of the radio structure that are correlated with Bgg. Correlations between physical size and hot spot placement with Bgg show evidence for an ICM only at z≤0.4, but there are no correlations at z≥0.4, suggesting an epoch of z∼0.4 for the formation of the ICM in these Abell richness class 0-1, FR2-selected clusters. X-ray-selected clusters at comparable redshifts, which contain FR1 type sources exclusively, are demonstrably richer than the FR2-selected clusters found in this study. The majority of the radio sources with high Bgg values at z≤0.4 can be described as fat doubles'' or intermediate FR2-FR1s. The lack of correlation between Bgg and β or Bgg and Q suggests that these types of radio source distortion are caused by something other than interaction with a dense ICM. Therefore, a large β cannot be used as an unambiguous indicator of a rich cluster around powerful radio sources. These results support the hypothesis made in our earlier paper that cluster quasars fade to become FR2s, then FR1s, on a timescale of 0.9 Gyr (for H0=50 km.s–1.Mpc–1).

Journal keyword(s): Galaxies: Active - Galaxies: Clusters: General - Galaxies: Evolution - Galaxies: Quasars: General - Radio Continuum

CDS comments: Table 2 : MS 2301.5+1506 is 2301.3+1506 (1E 2301.3+1506)