Gemini Long-slit Observations of Luminous Obscured Quasars: Further
  Evidence for an Upper Limit on the Size of the Narrow-Line Region
  We examine the spatial extent of the narrow-line regions (NLRs) of a sample
of 30 luminous obscured quasars at $0.4 < z < 0.7$ observed with spatially
resolved Gemini-N GMOS long-slit spectroscopy. Using the [OIII]$\lambda5007$
emission feature, we estimate the size of the NLR using a cosmology-independent
measurement: the radius where the surface brightness falls to 10$^{-15}$ erg
s$^{-1}$ cm$^{-2}$ arcsec$^{-2}$. We then explore the effects of atmospheric
seeing on NLR size measurements and conclude that direct measurements of the
NLR size from observed profiles are too large by 0.1 - 0.2 dex on average, as
compared to measurements made to best-fit S\'{e}rsic or Voigt profiles
convolved with the seeing. These data, which span a full order of magnitude in
IR luminosity ($\log{(L_{8 \mu \mathrm{m}} / \mathrm{erg\, s}^{-1})} = 44.4 -
45.4$) also provide strong evidence that there is a flattening of the
relationship between NLR size and AGN luminosity at a seeing-corrected size of
$\sim 7$ kpc. The objects in this sample have high luminosities which place
them in a previously under-explored portion of the size-luminosity
relationship. These results support the existence of a maximal size of the
narrow-line region around luminous quasars; beyond this size either there is
not enough gas, or the gas is over-ionized and does not produce enough
[OIII]$\lambda5007$ emission.
