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Published online by Cambridge University Press: 14 August 2015
In addition to the occurrence of emission line regions coexistent with extended radio sources which have been discussed at this Symposium, this phenomenon has been observed earlier in 3C277.3 (Miley et al. 1981) and in Centaurus A (Graham and Price 1981). This gas has been detected only in the Fanaroff and Riley “Class I” radio sources. Data concerning this class of object suggest that outflow from the nucleus is proceeding at transonic or subsonic speeds and this correlation has led to the suggestion (De Young 1981) that the origin of the emission line gas arises from entrainment of the interstellar medium into the ejected material.