An 80-kpc Lyman-alpha halo around a high redshift type-2 QSO

TL;DR

This paper reports the discovery of an extensive 80-kiloparsec Lyman-alpha halo around a high-redshift type-2 QSO, revealing insights into the galaxy's ionization, structure, and relation to radio activity at z=2.85.

Contribution

It presents the first detection of a large Lyman-alpha halo around a less luminous, high-redshift type-2 QSO, expanding understanding of galaxy halos beyond radio-loud AGN.

Findings

Halo extends over ~80 kpc at z=2.85.

Radio emission is ~50% extended beyond the core.

Optical emission consistent with AGN ionization.

Abstract

We announce the discovery of an extended emission line region associated with a high redshift type-2 QSO. The halo, which was discovered in our new wide-field narrow-band survey, resides at z = 2.85 in the Spitzer First Look Survey region and is extended over ~80 kpc. Deep VLBI observations imply that approximately 50 per cent of the radio emission is extended on scales > 200pc. The inferred AGN luminosity is sufficient to ionize the extended halo, and the optical emission is consistent with being triggered coevally with the radio source. The Lyman-alpha halo is as luminous as those found around high redshift radio galaxies, however the active nucleus is several orders of magnitude less luminous at radio wavelengths than those FRIIs more commonly associated with extended emission line regions. AMS05 appears to be a high-redshift analogue to the radio-quiet quasar E1821+643 which is core dominated but which also exhibits extended FRI-like structure and contains an optically powerful AGN. We also find evidence for more quiescent kinematics in the Lyman-alpha emission line in the outer regions of the halo, reminiscent of the haloes around the more powerful FRIIs. The optical to mid-infrared SED is well described by a combination of an obscured QSO (L_bol ~3.4 +/- 0.2 x 10^13 Lsolar) and a 1.4 Gyr old simple stellar population with mass ~3.9 +/- 0.3 x 10^11 Msolar.