VLT and GTC observations of SDSS J0123+00: a type 2 quasar triggered in a galaxy encounter

We present long-slit spectroscopy, continuum and [OIII] {$łambda$}5007 imaging data obtained with the Very Large Telescope and the Gran Telescopio Canarias of the type 2 quasar SDSS J0123+00 at z = 0.399. The quasar lies in a complex, gas-rich environment. It appears to be physically connected by a tidal bridge to another galaxy at a projected distance of \~{}100kpc, which suggests this is an interacting system. Ionized gas is detected to a distance of at least \~{}133kpc from the nucleus. The nebula has a total extension of \~{}180kpc. This is one of the largest ionized nebulae ever detected associated with an active galaxy. Based on the environmental properties, we propose that the origin of the nebula is tidal debris from a galactic encounter, which could as well be the triggering mechanism of the nuclear activity. SDSS J0123+00 demonstrates that giant, luminous ionized nebulae can exist associated with type 2 quasars of low radio luminosities, contrary to expectations based on type 1 quasar studies. Based on observations carried out at the European Southern Observatory (Paranal, Chile) with FORS2 on VLT-UT1 [programme 69.A-0123(A)] and at the Observatory Roque de los Muchachos (La Palma, Spain) with OSIRIS on GTC (programme GTC27-09A). E-mail: montse@iaa.es