The Central Region of the Barred Spiral Galaxy NGC1097 Probed by AKARI Near-Infrared Spectroscopy

TL;DR

This study used AKARI near-infrared spectroscopy to spatially resolve and analyze the starburst ring and central region of galaxy NGC1097, revealing diverse environments and grain structures without evidence of nuclear activity.

Contribution

First detailed spatially resolved near-infrared spectral analysis of NGC1097's central region and starburst ring, highlighting environmental variations and grain structure differences.

Findings

Distinct spatial distributions of hydrocarbon features and hydrogen emission.

Enhanced aliphatic features near the bar connecting the ring and nucleus.

Dominance of old stellar populations inside the ring without nuclear activity evidence.

Abstract

With the Infrared Camera on board AKARI, we carried out near-infrared (2.5-5.0 micron) 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 micron, the aliphatic hydrocarbon 3.4-3.6 micron features, and the hydrogen Br alpha 4.05 micron 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.