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 ] \lambda 5007 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 Sérsic 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 ] \lambda 5007 emission .