Infrared Spectroscopy of Nearby Radio Active Early-Type Galaxies -- II: Spectral Atlas

We present a near infrared spectroscopic atlas of nearby, bright early-type galaxies with radio emission, containing 163 galaxies observed by the Palomar 200" TripleSpec instrument, measuring the emission line fluxes for H, He, [Fe II] and H\(_2\) and determined the nuclear excitation mechanisms. By stacking spectra, we deduced the H\(_2\) excitation temperature (\(1957\pm182\) K) and dominant excitation mechanism (thermal and shock heating combined) from the \(\textit{K}\)-band emission line sequence. Stacking also produces an "average" spectrum of absorption features and spectral indices from the literature; the CO12 absorption line index vs. \(\textit{J-K}\) colour shows a trend of stronger nuclear activity producing a weaker CO12 index and a redder (flatter) continuum. The correlations between the radio and the emission-line luminosities finds a trend with radio power; however, the large scatter in the upper limits shows that the two are not directly coupled and the duty cycles of SF and AGN activity are not synchronised.