Near Infrared Spectroscopy of LINER Galaxies

Citation

Larkin, James Edwin (1996) Near Infrared Spectroscopy of LINER Galaxies. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/0G7Z-BS49. https://resolver.caltech.edu/CaltechTHESIS:05292018-163017352

Abstract

This thesis reports the design and operation of a new near infrared spectrograph for the 5 m Hale telescope and its use to observe a sample of LINER galaxies. The spectrograph operates between 1 and 5 microns using existing infrared array cameras. It has two long-slit spectroscopy modes yielding resolutions (λ/Δλ) of ~850 and ~3300 with a 0.75" wide by 40" long slit. The spectrograph also has a direct imaging mode giving a 10"x40" field of view.

The galaxy sample includes 15 LINERs with spectra covering the [Fell](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. The sample included, twelve low luminosity objects (classical LINERs) selected from sur­veys of nearby galaxies, and four high luminosity multiple nuclei systems.

All of the classical 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 compared to other galaxy types. The LINERs with the highest [Fell]/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 is 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.

The two multiple nuclei LINERs with line detections, IRAS 17132+5313 and Arp 220, had lower ratios of [Fell]/Paβ and/or H₂/Brγ than the classical LIN­ERs. The spectra of Arp 220 show that the extended emission has higher ratios of [Fell]/Paβ and H₂/Brγ than found on the nuclei. It is suggested that in these merging systems, the low ionization line emission probably results from shocks, ei­ther from cloud-cloud collisions or winds in the gas surrounding the nuclei.

Thesis Files