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arXiv · 1203.2794

AKARI near-infrared spectroscopy of the aromatic and aliphatic hydrocarbon emission features in the galactic superwind of M 82

M. Yamagishi·H. Kaneda·D. Ishihara·T. Kondo·T. Onaka·T. Suzuki·Y. C. Minh
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Abstract

Aims. We investigate the properties of hydrocarbon grains in the galactic superwind of M 82. Methods. With AKARI, we performed near-infrared (2.5 - 4.5 um) spectroscopic observations of 34 regions in M 82 including its northern and southern halos. Results. Many of the spectra show strong emission at 3.3 um due to polycyclic aromatic hydrocarbons (PAHs) and relatively weak features at 3.4 - 3.6 um due to aliphatic hydrocarbons. In particular, we clearly detect the PAH 3.3 um emission and the 3.4 - 3.6 um features in halo regions, which are located at a distance of 2 kpc away from the galactic center. We find that the ratios of the 3.4 - 3.6 um features to the 3.3 um feature intensity significantly increase with distance from the galactic center, while the ratios of the 3.3 um feature to the AKARI 7 um band intensity do not. Conclusions. Our results clearly confirm the presence of small PAHs even in a harsh environment of the halo of M 82. The results also reveal that the aliphatic hydrocarbons emitting the 3.4 - 3.6 um features are unusually abundant in the halo, suggesting that small carbonaceous grains are produced by shattering of larger grains in the galactic superwind.

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M. Yamagishi, H. Kaneda, D. Ishihara, T. Kondo, T. Onaka, T. Suzuki, Y. C. Minh. 2012-03-13. AKARI near-infrared spectroscopy of the aromatic and aliphatic hydrocarbon emission features in the galactic superwind of M 82. https://doi.org/10.1051/0004-6361%2F201218904

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