Observations at five radio frequencies are used to determine the structure and spectra of a complex region in the direction 0648 + 19. We show that it consists of three separate radio sources; two tailed sources in one cluster, and an unrelated classical double. We have used spectral-ageing calculations to derive ages and velocities for the two tailed sources. Combining these results with other data on head–tail sources and the sample observed by O'Dea, we discuss whether galaxy motion alone can account for the distribution of plasma. We find that the velocities derived from spectral ageing are not consistent with this hypothesis and favour an explanation which includes bulk streaming in the tails at velocities of several thousand km s–1.
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Ronghui Liu, Julia Riley, Peter Warner, Guy Pooley, Paul Alexander. The structure and dynamics of two tailed sources in cluster 0648 + 19, Monthly Notices of the Royal Astronomical Society, 1989, 501-511, DOI: 10.1093/mnras/240.3.501