Near-Infrared Spectra of Ultraluminous Infrared Galaxies

Abstract

Near-infrared spectra with a resolution of lambda&solm0;Deltalambda approximately 1100 in the rest-wavelength range of 1.8-2.2 µm have been obtained for a complete sample of 33 ultraluminous infrared galaxies (ULIRGs). Of the 33 objects observed, two show evidence of a central active galactic nucleus (AGN) through either a broad Paschen-alpha line or emission in the 1.963 µm fine structure of [Si vi]. In the median spectrum of the remaining 31 objects, the lines present are recombination lines of hydrogen and neutral helium, vibration-rotation lines of H2, and [Fe ii]. There is no indication of AGN activity in the median spectrum, either through broad atomic recombination lines or through high ionization lines. No trends in luminosity are apparent when subsets of the 31 non-AGN ULIRGs are binned by luminosity and median-combined. When secondary nuclei exist in ULIRGs, they typically have spectra very much like those seen in the primary nuclei.

Follow-up near-infrared spectroscopy of ultraluminous infrared galaxies observed by ISO

“…In most of our ULIRGs, the Paα line shows a blue wing (see also Veilleux et al 1997bVeilleux et al , 1999bBurston et al 2001). Murphy et al (1999Murphy et al ( , 2001) resolved similar blue wings and proposed an identification with two helium recombination lines at 1.8686 and 1.8697 µm. Transitions of molecular hydrogen may contribute as well (Veilleux et al 1999b).…”

“…With the advent of sensitive near-infrared detectors, near-infrared spectroscopy of ultraluminous galaxies (e.g., Goldader et al 1995Goldader et al , 1997aVeilleux et al 1997bVeilleux et al , 1999bMurphy et al 1999Murphy et al , 2000Murphy et al , 2001Burston et al 2001;Valdés et al 2005) began to unveil the nature of these most luminous galaxies in the local universe. Most near-infrared spectra of ULIRGs were found to be starburst-like, but the starburst luminosity traced by the observations appeared typically insufficient to account for the full ULIRG luminosities.…”

Early-type galaxies in the near-infrared: 1.5–2.4 $\mu{\rm m}$ spectroscopy

“…Most of the previous work at NIR was focused on either active galactic nuclei (AGNs) or objects with very strong star formation, including recent surveys of ultra-luminous infrared galaxies (Goldader et al 1995;Murphy et al 1999Murphy et al , 2001Burston et al 2001), luminous infrared galaxies (Goldader et al 1997;Reunanen et al 2007), starbursts (Engelbracht 1997;Coziol et al 2001), Seyfert galaxies (Ivanov et al 2000;Sosa-Brito et al 2001;Reunanen et al 2002;Boisson et al 2002), LINERs (Larkin et al 1998;Alonso-Herrero et al 2000;Sosa-Brito et al 2001), and interacting galaxies (Vanzi & Rieke 1997;Vanzi et al 1998). …”

Investigating the central engine and excitation mechanisms of ultraluminous infrared galaxies: near-infrared spectroscopy

“…One possibility is the faint H 2 emission from the O(3) 1.8721 μm and O(5) 1.8665 μm transitions (Veilleux et al 1997, 1999b). Another possibility is the presence of a pair of He i emission lines at 1.8686 and 1.8697 μm (Murphy et al 1999). At the spectral resolution of our data we cannot distinguish between these possibilities.…”

“…They have imaged these galaxies in the optical and the NIR, and have found a high percentage to be interacting (95 per cent). They have also obtained NIR spectral data for 33 of these objects for which results have recently been published (Murphy et al 1999, 2001). Finally, Veilleux, Sanders & Kim (1997, 1999b) have conducted a campaign aimed at uncovering hidden broad line regions in ULIRGs.…”