Shocks, illumination cones and intrinsic gas structures in the extreme radio galaxy 3C 265.

We present deep, narrow-band and continuum images of the powerful high-redshift radio galaxy 3C 265 (z=0.811) , taken with the TAURUS Tunable Filter on the William Herschel Telescope, together with detailed long-slit spectroscopic observations along the axis defined by the UV/optical emission elongation. The deep images reveal the existence of cones in the ionization structure of 3C 265 within ∼7 arcsec (58 kpc) of the nucleus, where the emission-line structure is not observed to be closely aligned with the radio axis. This indicates that anisotropic illumination from the central active nucleus dominates on a small scale. In contrast, at larger distances (≳10 arcsec; 80 kpc) from the nucleus, low-ionization emission gas is closely aligned with the radio axis, suggesting that jet–cloud interactions may become the dominant mechanism in the line-emitting gas on a larger scale. Moreover, the presence of a high-velocity cloud at 2.5 arcsec from the nucleus, close to the radio axis, indicates that even close to the nucleus (∼20 kpc) jet-induced shocks have an important kinematic effect. However, spectroscopic analysis of this region reveals that the ionization state of the high-velocity gas is similar to or higher than that of the surroundings, which is opposite to what we would expect for a cloud that has been compressed and accelerated by jet-induced shocks. Our images show that, while on a large scale the low-ionization emission-line structures are aligned with the radio axis, on a smaller scale, where AGN-photoionization dominates, the highest surface-brightness structure is aligned with the closest companion galaxy (misaligned with the radio axis). This suggest that much of the emission-line structure reflects the intrinsic gas distribution, rather than the ionization pattern imprinted by the radio jets or by illumination from the central AGN. Overall, our results underline the need for a variety of mechanisms to explain the properties of the extended emission-line gas in the haloes of radio galaxies. [ABSTRACT FROM AUTHOR]