The [NII] 205 μm line emission from high-z submillimeter galaxies and quasar host galaxies
Authors: Kolupuri Saimurali , Decarli Roberto , Neri Roberto , Cox Pierre , Ferkinhoff Carl , Bertoldi Frank , Weiss Axel , Venemans Bram P. , Riechers Dominik A. , Paolo Farina Emanuele , Walter Fabian 
Published: February 2025

We present NII 205 μm fine structure line observations of three submillimeter galaxies (SMGs) and three quasar host galaxies (QSOs) at 4lesssimzlesssim6 using the Institut de radioastronomie millim'etrique (IRAM) interferometer. The NII emission is detected in three sources, and we report detections of the underlying dust continuum emission in all sources. The observed NII -to-infrared luminosity ratio spans at least 0.5 dex for our sources. Comparing our estimates with sources detected in the NII 205 μm at similar redshifts shows that the overall NII -to-IR luminosity ratio spans over 1 dex in magnitude from L_ NII /L_IR ∼ 10^-4 -- 10^-5 and follows the trend of the so-called NII fine structure line deficit observed in (ultra)-luminous IR galaxies in the local Universe. The CII -to- NII luminosity ratio is greater than ten for most of our sources, indicating that the bulk of the CII 158 μm line emission ( f CII ^PDR) >75%) arises from the neutral medium. From our analysis, we do not find significant differences in the NII 205 μm emission and the respective ratios between SMGs and QSOs, suggesting a negligible contribution to the boosting of NII 205 μm emission due to the active galactic nucleus (AGN) photoionization. Future investigations involving other fine structure lines and optical diagnostics will provide further insight into a suite of ionized medium properties and reveal the diversity between AGN and non-AGN environments. We present NII 205 μm fine structure line observations of three submillimeter galaxies (SMGs) and three quasar host galaxies (QSO) at 4lesssimzlesssim6 using the Institut de radioastronomie millim'etrique (IRAM) interferometer. The NII emission is detected in three sources, and we report detections of the underlying dust continuum emission in all sources. The observed NII -to-infrared (IR) luminosity ratio spans at least 0.5 dex for our sources. Comparing our estimates with sources detected in the NII 205 μm at similar redshifts shows that the overall NII -to-IR luminosity ratio spans over a dex in magnitude from L_ NII /L_IR ∼ 10^-4 -- 10^-5 and follows the trend of the so-called NII fine structure line deficit observed in (ultra)-luminous infrared galaxies in the local Universe. The CII -to- NII luminosity ratio is >10 for most of our sources, indicating that the bulk of the CII 158 μm line emission ( f CII ^PDR) >75%) arises from the neutral medium. From our analysis, we do not find significant differences in the NII 205 μm emission and the respective ratios between SMGs and QSOs, suggesting a negligible contribution to the boosting of NII 205 μm emission due to the active galactic nucleus (AGN) photoionization. Future investigations involving other fine structure lines and optical diagnostics will provide further insight into a suite of ionized medium properties and reveal the diversity between AGN and non-AGN environments.