[NII]205um emission in local luminous IR galaxies

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.