Journal
ASTRONOMY & ASTROPHYSICS
Volume 541, Issue -, Pages -Publisher
EDP SCIENCES S A
DOI: 10.1051/0004-6361/201218904
Keywords
ISM: jets and outflows; ISM: lines and bands; galaxies: individual: M 82; galaxies: starburst; infrared: galaxies
Categories
Funding
- [23005457]
- [22340043]
- Grants-in-Aid for Scientific Research [11J05457, 22340043, 23244021, 24740122] Funding Source: KAKEN
- National Research Council of Science & Technology (NST), Republic of Korea [2012151000] Funding Source: Korea Institute of Science & Technology Information (KISTI), National Science & Technology Information Service (NTIS)
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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 mu m) 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 mu m caused by polycyclic aromatic hydrocarbons (PAHs) and relatively weak features at 3.4-3.6 mu m caused by aliphatic hydrocarbons. In particular, we clearly detect the PAH 3.3 mu m emission and the 3.4-3.6 mu m 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 mu m features to the 3.3 mu m feature intensity significantly increase with distance from the galactic center, while the ratios of the 3.3 mu m feature to the AKARI 7 mu m band intensity do not. Conclusions. Our results clearly confirm the presence of small PAHs even in the harsh environment of the halo of M 82. The results also reveal that the aliphatic hydrocarbons emitting the 3.4-3.6 mu m 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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