The central region of the barred spiral galaxy NGC1097 probed by AKARI near-infrared spectroscopy

With the Infrared Camera on board AKARI, we carried out near-infrared (2.5-5.0 μm) spectroscopy of the central kiloparsec region of the barred spiral galaxy, NGC1097, categorized as Seyfert 1 with a circumnuclear starburst ring. Our observations mapped the area of 50″ × 10″ with the resolution of 5″, covering about a half of the ring and the galactic center. As a result, we spatially resolve the starburst ring in the polycyclic aromatic hydrocarbon 3.3 μm, the aliphatic hydrocarbon 3.4-3.6 μm features, and the hydrogen Brα 4.05 μm emission. They exhibit spatial distributions significantly different from each other, indicating that the environments vary considerably around the ring. In particular, the aliphatic features are enhanced near the bar connecting the ring with the nucleus, where the structure of hydrocarbon grains seems to be relatively disordered. Near the center, the continuum emission and the CO/SiO absorption features are strong, which indicates that the environments inside the ring are dominated by old stellar populations. The near-infrared spectra do not show any evidence for the presence of nuclear activity.