First detections of the [NII] 122 {\mu}m line at high redshift:
  Demonstrating the utility of the line for studying galaxies in the early
  universe
  We report the first detections of the [NII] 122 {\mu}m line from a high
redshift galaxy. The line was strongly (> 6{\sigma}) detected from
SMMJ02399-0136, and H1413+117 (the Cloverleaf QSO) using the Redshift(z) and
Early Universe Spectrometer (ZEUS) on the CSO. The lines from both sources are
quite bright with line-to-FIR continuum luminosity ratios that are
~7.0\times10^{-4} (Cloverleaf) and 2.1\times10^{-3} (SMMJ02399). With ratios
2-10 times larger than the average value for nearby galaxies, neither source
exhibits the line-to-continuum deficits seen in nearby sources. The line
strengths also indicate large ionized gas fractions, ~8 to 17% of the molecular
gas mass. The [OIII]/[NII] line ratio is very sensitive to the effective
temperature of ionizing stars and the ionization parameter for emission arising
in the narrow-line region (NLR) of an AGN. Using our previous detection of the
[OIII] 88 {\mu}m line, the [OIII]/[NII] line ratio for SMMJ02399-0136 indicates
the dominant source of the line emission is either stellar HII regions ionized
by O9.5 stars, or the NLR of the AGN with ionization parameter log(U) = -3.3 to
-4.0. A composite system, where 30 to 50% of the FIR lines arise in the NLR
also matches the data. The Cloverleaf is best modeled by a superposition of
~200 M82 like starbursts accounting for all of the FIR emission and 43% of the
[NII] line. The remainder may come from the NLR. This work demonstrates the
utility of the [NII] and [OIII] lines in constraining properties of the ionized
medium.
