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

Abstract

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.

Defying jet-gas alignment in two radio galaxies atz~ 2 with extended light profiles: Similarities to brightest cluster galaxies

“…5). Off-axis gas not aligned with the radio jet axis and out to a galactocentric radius of 65 kpc in the radio galaxy 3C 265 at z = 0.8 may indeed be powered by shocks, perhaps with additional photoionization from soft X-ray emission from the precursor of the shock (Solórzano-Iñarrea et al 2002). However, as argued by Le Tiran et al (2011) and Nesvadba et al (2006), it is difficult to reach high Hα surface brightnesses as observed with shocks.…”

INTEGRAL spectroscopy of three powerful radio galaxies: jet--cloud interactions seen in three dimensions

“…It has an extreme emission‐line luminosity (McCarthy 1988), which makes 3C 265 ideal for the study of emission‐line properties in distant radio galaxies. Its continuum structure extends over more than 10 arcsec and [O ii ]λ3727 images show emission over more than 30 arcsec (Rigler et al 1992; McCarthy, Spinrad & van Breugel 1995; Solórzano‐Iñarrea et al 2002). HST images reveal the bizarre optical morphology of this object, with the nucleus surrounded (in projection) by emission regions or companion galaxies (Longair, Best & Rottgering 1995).…”

“…The ionization of these EELR is thought to be due to a combination of photoionization by the central AGN and shocks induced by interactions with the radio source, with AGN photoionization dominating near the nucleus, and jet–cloud interactions becoming more important at larger radii (e.g. Solórzano‐Iñarrea, Tadhunter & Bland‐Hawthorn 2002). By investigating the properties of these EELR we can learn about the interactions between the radio source and its environment.…”

The nature of the jet-driven outflow in the radio galaxy 3C 305

“…Baum & Heckman ; Tadhunter et al ) is whether these EELR are ionized by photons from the nucleus or by shocks driven by the jets; in the most powerful radio sources, normally found at high redshift, there is often evidence that the optical emission‐line material is either ionized or at least strongly affected by jet‐driven shocks, which requires a direct interaction between the jets and the warm/cold ( T < 10 4 K) phase of the interstellar medium (ISM) of the host galaxy (e.g. Sólorzano‐Iñarrea, Tadhunter & Bland‐Hawthorn ; Nesvadba et al ).…”