On the jet speeds of classical double radio sources

.S.Longair A sim ple integralrelation isobtained forthe distribution functionsofjetspeedsand jet-counterjet(cid:13)ux asym m etriesofclassicaldoubleradio sourceson thebasisofa sim ple m odelin which it is assum ed that the jets are intrinsically sym m etric and that the asym m etriesare attributed to relativistic beam ing.Analytic expressionsrelating the m ean jetspeed and the m ean jet(cid:13)ux asym m etry,and theirvariancesarederived. The results are considered in the light oforientation-based uni(cid:12)ed schem es,and an analyticalequation for the criticalangle separating quasarsand radio galaxiesis de-rived.The m ean jet speeds ofclassicaldouble radio sources are estim ated using the asym m etry ofjet-counterjet(cid:13)ux densitiestaken from the 3CRR and B2 sam ples.For FRIradio sourcesthe m ean jetspeed is (cid:24) (0 : 54 (cid:6) 0 : 03) c ,while forFRIIlow-redshift radio galaxiesand interm ediate redshiftquasarsthe valuesfound are (cid:24) (0 : 4 (cid:6) 0 : 06) c and