151-MHz and 1.5-GHz observations of bridges in powerful extragalactic radio sources

We have observed seven 3C quasars and 12 3C radio galaxies with $$P_{178}\gt10^{27}\enspace \text W \enspace \text {Hz}^{-1}\enspace \text {sr}^{-1}$$ using MERLIN at 151 MHz and the VLA at 1.5 GHz. This is the first time that a significant number of objects has been mapped at such high resolution at wavelengths longer than 1 m. We detected complete bridges in 15 sources, and extended tails to the hotspots in the remaining four. The trend found previously for bridges to become more elongated in powerful sources is confirmed. As at higher frequencies, the spectra of bridges steepen away from the hotspots, with the spectral index α rising to 1.4–2.0 at the centre, between emitted frequencies of 0.3 and 3 GHz. Compared with radio galaxies of similar powers, bridges in quasars are stubbier and more distorted, suggesting that the long-term stability of the collimation is poorer in quasars than in radio galaxies. Finally, in three cases the hotspot spectra show low-frequency flattening, which appears to be due to a departure from a power-law of the electron-energy distribution at low energy.