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 ($1957\pm 182$ K) and dominant excitation mechanism (thermal and shock heating combined) from the $\mathit{\text{K}}$-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. $\mathit{\text{J-K}}$ 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.