Polarized light in high-redshift radio galaxies
HIGH-redshift radio galaxies are characterized by ultraviolet excesses1,2 associated with elongated continuum and emission-line structures aligned along their radio axes3,4. Commonly, these properties are interpreted in terms of jet-induced star formation. However, observations of a blue, polarized continuum knot in the low-redshift radio galaxy PKS2152 — 69 have suggested an alternative beaming/scattering model5,6. To test this model we have obtained imaging-polarimetry observations of two high-redshift radio galaxies: 3C277.2 (z = 0.766) and 3C368 (z = 1.132). We find that both sources are strongly linearly polarized at ultraviolet rest wavelengths, with E-vectors within 25° of perpendicular to the axis of the extended continuum and radio structures. This implies that a large proportion of the ultraviolet light in these objects does not come directly from stars and we suggest it is scattered radiation from the nucleus. These observations also have important implications for beaming models of the active nuclei and for our understanding of the evolution of the host galaxies.
A blue, polarized continuum source near radio galaxy PKS2152–69
The frequent occurrence of extranuclear emission line regions in radio galaxies and quasars is well known1,2, but the origin and excitation of gas at temperatures of (l–2) × 104 K, extending to distances beyond 100 kpc from the nucleus, are not understood in detail. In some cases there is evidence that highly excited gas is associated with the transport of energy from the active nucleus of the galaxy out to the extended radio structures, and in one such case, the radio galaxy PKS2152–69, Tadhunter et al.3 reported a blue continuum source coincident with the highest ionization region of a gas cloud, at a projected distance of 8 kpc from the nucleus and lying approximately along the radio axis. Here we report optical observations of the continuum showing that its spectrum rises into the near ultraviolet with fv∝v3±1 and that its degree of polarization is about 10% with the electric vector perpendicular to the radius vector from the nucleus. In the absence of a workable intrinsic emission mechanism, we propose that a beamed nuclear source could excite the highly ionized extranuclear cloud and scatter off associated dust to produce the observed continuum.
An X-ray survey of a complete sample of 3CR radio galaxies.
On presente les resultats de l'observation RX faite par l'Observatoire Einstein de 40 radiogalaxies 3CR. Vingt six galaxies ont ete detectees en RX avec des luminosites RX (0,5-3,0 keV) comprises entre 10 41 et 10 45 ergs. s −1 . On trouve que les galaxies 3CR a morphologie radio double (FR2) et a spectre de raies d'emission optique ont tendance a etre des emetteurs RX plus puissants, avec les galaxies a raies larges au sommet de la distribution. On trouve egalement que la luminosite RX est en correlation avec la luminosite radionucleaire a 5 GHz. Les resultats de l'etude montrent l'importance des phenomenes nucleaires dans les radiogalaxies et suggerent une origine nucleaire pour leur emission RX