Spitzer Space Telescope - General Observer Proposal #20753


The origin of extended Lyman-alpha around a z=4.5 QSO

Principal Investigator: Andrew Bunker
           Institution: University of Exeter

Co-Investigators: 
Daniel Stern, Jet Propulsion Laboratory                               

Science Category: AGN/quasars/radio galaxies 
 Observing Modes: IracMap MipsPhot 
  Hours Approved: 6.2 

Abstract:
We have discovered extended Lyman-alpha emission around a z=4.5 QSO in
a deep long-slit spectrum with Keck/LRIS.  The line emission extends
5arcsec beyond the continuum of the QSO and is spatially asymmetric.
This extended line emission has a spectral extent of 1000km/s, much
narrower in velocity spread than the broad Lyman-alpha from the QSO
itself and slightly offset in redshift.  No evidence of continuum is
seen for the extended emission line region.  This phenomenon is rare
in QSOs which are not radio loud, and this is the first time it has
been observed at z>4.  It is possible that the QSO is illuminating the
surrounding cold gas of the host galaxy, with the ionizing photons
producing Lyman-alpha fluorescence.  As suggested by Haiman & Rees
(2001), this "fuzz" around a distant quasar may place strong
constraints on galaxy formation and the extended distribution of cold,
neutral gas.  Alternatively, the Lyman-alpha may be powered locally by
star formation in a galaxy-wide starburst.  By searching for stellar
continuum at longer wavelengths with IRAC, we can discriminate between
these theories.  We have also discovered a Lyman-alpha "blob" at the
QSO redshift and only 23arcsec (150kpc) away:  MIPS imaging will
reveal whether this is a ULIRG-like buried source, or if it is being
photoionized by the QSO.