The large-scale distribution of warm ionized gas around nearby radio galaxies with jet-cloud interactions

Deep, narrow-band H alpha observations taken with the TAURUS Tunable Filter on the 4.2-m William Herschel Telescope are presented for two nearby radio galaxies with strong jet-cloud interactions. Although the brightest emission-line components are closely aligned with the radio jets - providing nearby examples of the 'alignment effect' most commonly observed in high-redshift (z > 0.5) radio galaxies - lower surface brightness emission-line structures are detected at large distances (tens of kpc) from the radio jet axis. These latter structures cannot be reconciled with anisotropic illumination of the interstellar medium by obscured quasar-like sources, because parts of the structures lie outside any plausible quasar ionization cones, Rather, the distribution of the emission lines around the fringes of the extended radio lobes suggests that the gas is ionized either by direct interaction with the radio components, or by the diffuse photoionizing radiation fields produced in the shocks generated in such interactions. These observations serve to emphasize that the ionizing effects of the radio components can extend far from the radio jet axes, and that deep emission-line imaging observations are required to reveal the true distribution of warm gas in the host galaxies. We expect future deep imaging observations to reveal similar structures perpendicular to the radio axes in high-z radio galaxies.