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