  Luminous extended emission-line regions (EELRs) on kpc scales surround a
substantial fraction of steep-spectrum radio-loud QSOs. Although their
existence has been known for over three decades, there are still major
uncertainties on the physical processes responsible for their complex
morphology and kinematics. We are obtaining deep integral field spectroscopy
for a sample of EELRs around QSOs at z<0.5 with the Integral Field Unit (IFU)
of the GMOS on the Gemini North telescope, aiming at extracting accurate
kinematics of the EELRs, measuring important physical parameters (e.g.,
density, temperature, metallicity) and reliable intensity ratios of diagnostic
emission lines from individual clouds that comprise an EELR. Here we present
results from the observations of the EELR of quasar 4C 37.43. We show maps of
gas kinematics measured from the [O III] 5007 line and line-ratio diagnostic
diagrams comparing the data with predictions from ionization models. We find
that the ionized gas shows rather complex global kinematics, while linear
velocity gradients are often seen in individual clouds. Pure photoionization by
the QSO continuum is the most likely ionization mechanism for most of the EELR
clouds.

Astrophysics