We report the discovery of Seyfert-2 galaxies in SDSS-DR8 with galaxy-wide , ultra-luminous narrow-line regions ( NLRs ) at redshifts z = 0.2 - 0.6 .
With a space density of 4.4 Gpc ^ { -3 } at z \sim 0.3 , these “ Green Beans ” ( GBs ) are amongst the rarest objects in the Universe .
We are witnessing an exceptional and/or short-lived phenomenon in the life cycle of AGN .
The main focus of this paper is on a detailed analysis of the GB prototype galaxy J2240-0927 ( z = 0.326 ) .
Its NLR extends over 26 \times 44 kpc and is surrounded by an extended narrow-line region ( ENLR ) .
With a total [ O iii ] \lambda 5008 luminosity of ( 5.7 \pm 0.9 ) \times 10 ^ { 43 } erg s ^ { -1 } , this is one of the most luminous NLR known around any type-2 galaxy .
Using VLT/XSHOOTER we show that the NLR is powered by an AGN , and we derive resolved extinction , density and ionization maps .
Gas kinematics is disturbed on a global scale , and high velocity outflows are absent or faint .
This NLR is unlike any other NLR or extended emission line region ( EELR ) known .
Spectroscopy with Gemini/GMOS reveals extended , high luminosity [ O iii ] emission also in other GBs .
WISE 24 \mu m luminosities are 5 - 50 times lower than predicted by the [ O iii ] fluxes , suggesting that the NLRs reflect earlier , very active quasar states that have strongly subsided in less than a galaxies ’ light crossing time .
These light echos , or ionization echos , are about 100 times more luminous than any other such echo known to date .
X-ray data are needed for photo-ionization modeling and to verify the light echos .