NIR lines for AGN up to z~3

However, this method is biased against dusty sources, hampering a complete census of the AGN population across cosmic epochs. To mitigate th is effect, it is crucial to observe at longer wavelengths in the rest-frame near-infrared (near-IR), which is less affected by dust attenuation and can thus provide a better description of the intrinsic properties of galaxies.

AGN diagnostics in this regime have not been fully exploited so far, due to the scarcity of near-IR observations of both AGNs and star-forming galaxies, especially at redshifts higher than 0.5. Using Cloudy photoionization models, we identified new AGN - star formation diagnostics based on the ratio of bright near-IR emission lines, namely [SIII] 9530{AA}, [CI] 9850{AA}, [PII] 1.188 micron, [FeII] 1.257 micron, and [FeII] 1.64 micron to Paschen lines (either Pa{gamma} or Pa{beta}), providing simple, analytical classification criteria.