A z=3.045 Lyman alpha emitting halo hosting a QSO and a possible candidate for AGN-triggered star-formation

TL;DR

This paper reports the discovery of a Lyman alpha emitting halo around a z=3.045 QSO, suggesting possible AGN-triggered star formation, based on deep spectroscopic and imaging data showing extended emission and a young stellar population.

Contribution

It provides evidence for AGN feedback triggering star formation in a high-redshift galaxy, combining spectroscopic, imaging, and photometric analysis.

Findings

Extended Lyman alpha halo around a z=3.045 QSO

Spatial coincidence with a faint, peculiar galaxy

Possible young stellar population near the AGN

Abstract

In this third paper in a series on the nature of extended, asymmetric Lyman alpha emitters at z ~ 3 we report the discovery, in an ultra-deep, blind, spectroscopic long-slit survey, of a Lyman alpha emitting halo around a QSO at redshift 3.045. The QSO is a previously known, obscured AGN. The halo appears extended along the direction of the slit and exhibits two faint patches separated by 17 proper kpc in projection from the QSO. Comparison of the 2-dimensional spectrum with archival HST ACS images shows that these patches coincide spatially with emission from a peculiar, dumbbell-shaped, faint galaxy. The assumptions that the Lyman alpha emission patches are originating in the galaxy and that the galaxy is physically related to the QSO are at variance with photometric estimates of the galaxy redshift. We show, however, that a population of very young stars at the redshift of the QSO may fit the existing rest frame broad band UV photometry of the galaxy. If this scenario is correct then the symmetry of the galaxy in continuum and Lyman alpha emission, the extension of the QSO's Lyman alpha emission in its direction, and the likely presence of a young stellar population in close proximity to a (short-lived) AGN suggest that this may be an example of AGN feedback triggering external star formation in high redshift galaxies.