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Description
In this paper, we present the measurements of the [NII]205{mu}m line for a flux-limited sample of 122 (ultra-)luminous infrared galaxies [(U)LIRGs] and 20 additional normal galaxies, obtained with the Herschel Space Observatory (Herschel). We explore the far-infrared (FIR) color dependence of the [NII]205{mu}m (L_[NII]205{mu}m_) to the total infrared (L_IR_) luminosity ratio, and find that L_[NII]205{mu}m_/L_IR_ only depends modestly on the 70-160{mu}m flux density ratio (f70/f160) when f70/f160<~0.6, whereas such dependence becomes much steeper for f70/f160>0.6. We also investigate the relation between L_[NII]205{mu}m_ and star formation rate (SFR), and show that L_[NII]205{mu}m_ has a nearly linear correlation with SFR, albeit the intercept of such a relation varies somewhat with f60/f100, consistent with our previous conclusion that [NII]205{mu}m emission can serve as an SFR indicator with an accuracy of ~0.4dex, or ~0.2dex if f60/f100 is known independently. Furthermore, together with the Infrared Space Observatory measurements of [NII], we use a total of ~200 galaxies to derive the local [NII]205{mu}m luminosity function (LF) by tying it to the known IR LF with a bivariate method. As a practical application, we also compute the local SFR volume density ({rho}_SFR_) using the newly derived SFR calibrator and LF. The resulting log{rho}_SFR_=-1.96+/-0.11M_{sun}_/yr/Mpc^3^ agrees well with previous studies. Finally, we determine the electron densities (n_e_) of the ionized medium for a subsample of 12 (U)LIRGs with both [NII]205{mu}m and [NII]122{mu}m data, and find that n_e_ is in the range of ~1-100/cm^3^, with a median value of 22/cm^3^.
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