A Near Infrared Spectroscopic Survey of LINER Galaxies

This paper reports the results of a near infrared spectroscopic survey of LINER galaxies undertaken with a new infrared spectrograph at the 5 m Hale telescope. The galaxy sample includes 11 LINERs with spectra covering the [FeII] (1.2567 μm), Paβ (1.2818 μm), H2 ( 1-0 S(1), 2.1218 μm) and Brγ (2.1655 μm) near infrared emission lines, and one additional galaxy with only [FeII] and Paβ line coverage. All of the LINERs with infrared line detections have strong [FeII] and/or H2 emission, with about half (4 out of 9) having extremely high ratios (>2) of [FeII] to Paβ. The strength of the H2 and [FeII] lines is well correlated with the optical [OI] line, with many LINERs having higher ratios of [FeII]/Paβ, H2/Brγ and [OI]/Hα than other galaxy types. The LINERs with the highest [FeII]/Paβ ratios (termed “strong” [FeII] LINERs) show evidence for recent star formation. Shocks from compact supernova remnants may enhance the [FeII] emission in these “strong” [FeII] LINERs. The LINERs with lower [FeII]/Paβ ratios (termed “weak” [FeII] LINERs) are more consistent with Seyfert-like activity, including higher ionization states, some strong x-ray sources and some broad Hα detections. The [FeII] luminosity and the [FeII]/Paβ ratio in these objects are more easily explained by hard x-ray excitation than in the “strong” [FeII] LINERs. These “weak” [FeII] LINERs are considered prime candidates for being low luminosity Seyfert nuclei.