@inproceedings{oai:jaxa.repo.nii.ac.jp:00003151,
 author = {矢野, 健一 and 中川, 貴雄 and Malkan, Matthew and 磯部, 直樹 and 白旗, 麻衣 and 馬場, 俊介 and 道井, 亮介 and Bhalotia, Vanshree and Yano, Kenichi and Nakagawa, Takao and Malkan, Matthew and Isobe, Naoki and Shirahata, Mai and Baba, Shunsuke and Doi, Ryosuke and Bhalotia, Vanshree},
 book = {宇宙航空研究開発機構特別資料, JAXA Special Publication: The Cosmic Wheel and the Legacy of the AKARI archive: from galaxies and stars to planets and life},
 month = {Mar},
 note = {第4回「あかり」国際会議 (2017年10月17-20日. 東京大学), 文京区, 東京, The 4th AKARI International Conference: The Cosmic Wheel and the Legacy of the AKARI archive: from galaxies and stars to planets and life (October 17-20, 2017. The University of Tokyo), Bunkyo-ku, Tokyo, Japan, We made systematic observations of the HI Br alpha (4.05 micrometers) and Br beta (2.63 micrometers) lines in 52 nearby (z less than 0.3) ULIRGs with AKARI. Our observations show that ULIRGs have a tendency to indicate higher Br beta/Br alpha line ratios than those observed in Galactic HII regions, and three galaxies in the observed sample show the anomaly of the Br beta/Br alpha line ratios (in the order of 1.0), which are significantly higher than that of case B (0.565). The high Br beta/Br alpha line ratios cannot be explained by the combination of the dust extinction and the case B, since dust extinction reduces the ratio. We simulate HII regions in the ULIRGs with the Cloudy code, and show that the high Br beta/Br alpha line ratios can be explained with the combination of the optically thick Br alpha line and the optically thin Br beta line. To achieve the column density large enough to make the Br alpha line optically thick, the gas density is required as high as n in the order of 10(exp 8) cm(exp -3). Hence our results suggest that star-formation activity in ULIRGs occurs preferentially in high-density clouds., 形態: カラー図版あり, Physical characteristics: Original contains color illustrations, 資料番号: AA1730026077, レポート番号: JAXA-SP-17-009E},
 pages = {379--382},
 publisher = {宇宙航空研究開発機構(JAXA), Japan Aerospace Exploration Agency (JAXA)},
 title = {Anomaly of Hydrogen Recombination Line Ratio in Ultraluminous Infrared Galaxies},
 volume = {JAXA-SP-17-009E},
 year = {2018}
}