Near- to Mid-Infrared Spectroscopy for the Giant Elliptical Galaxy NGC 1316 (Fornax A) with the AKARI Infrared Camera

Abstract

We present the near- to mid-infrared (∼2.5-13 μm) spectrum of the giant elliptical galaxy NGC 1316 (Fornax A) obtained with the Infrared Camera (IRC) on board AKARI. NGC 1316 is known to have a peculiar polycyclic aromatic hydrocarbon (PAH) emission spectrum with an unusually high ratio of the 11.3 μm to the 7.7 μm emission intensity through the Spitzer IRS observation. NGC 1316 is a 3 Gyr old merger remnant with a dormant nucleus that was rather active 0.1 Gyr ago; the relatively well-known evolutionary history makes the elliptical galaxy an ideal probe for studying long-term effects of past energetic events on the interstellar medium. We have found that there is no significant PAH emission feature at 3.3 mm while we have confirmed the peculiar PAH emission spectrum in the mid-infrared. We have detected a strong absorption feature at 4.3 μm, which may be attributed to solid-state CO2 in grain mantles. We discuss physical implications for those unusual emission and absorption features. © 2007. The American Astronomical Society.