A sample of Seyfert-2 galaxies with ultra-luminous galaxy-wide NLRs -- Quasar light echos?

TL;DR

This paper reports the discovery of rare, galaxy-wide ultra-luminous narrow-line regions in Seyfert-2 galaxies, suggesting they are light echoes of past quasar activity, with detailed analysis of a prototype galaxy revealing unique properties.

Contribution

It presents the identification and detailed analysis of ultra-luminous, galaxy-wide NLRs in Seyfert-2 galaxies, proposing they are quasar light echoes, a novel phenomenon in AGN lifecycle studies.

Findings

Discovery of ultra-luminous, galaxy-wide NLRs in Seyfert-2 galaxies.

NLRs are likely light echoes of past quasar activity.

The NLR in the prototype galaxy is among the most luminous known.

Abstract

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 per cubic Gpc at z~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 26x44 kpc and is surrounded by an extended narrow-line region (ENLR). With a total [OIII]5008 luminosity of (5.7+/-0.9)x10e43 erg/s, 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 [OIII] emission also in other GBs. WISE 24micron luminosities are 5-50 times lower than predicted by the [OIII] 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 are about 100 times more luminous than any other such light echo known to date. X-ray data are needed for photo-ionization modeling and to verify the light echos.