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Angular-Size and Angular-Velocity Redshift Relations for Quasars and AGN
Content
The angular size − redshift relation for radio galaxies was first discussed by Fred Hoyle at the 1957 Paris Symposium on Radio Astronomy. Unlike for optical measurements of angular size, which are systematically influenced by the effects of redshift and sky brightness, radio measurements of component separations are true metric rods. However attempts to observationally test the predicted dependence of the angular size of extended radio galaxies has been limited by evolutionary effects including the systematic dependence of radio galaxy dimensions on redshift. The compact radio sources associated with quasars and AGN are, by contrast, young compared with the age of the Universe so are not systemically affected by cosmic evolution Moreover as quasars are located in the nuclei of galaxies, unlike the extended radio galaxies, they are unaffected by the intergalactic medium and its dependence on red shift..
I have examined the observed angular size and apparent angular velocity dependence on redshift for the complete MOJAVE 1.5 Jy quarter-century (QC) flux-density-limited sample. The data are consistent with models having H0 = 70 km/sec/Mpc, ΩM = 0.3, and ΩDE = 0.7, but the existing data are inadequate to place significant limits on cosmological models. With the enhanced sensitivity and resolution of the ngVLA it will be possible to extend these studies to higher redshift quasars where there is a greater distinction among different cosmologies.