磯部 直樹

日本天文学会2023年春季年会, 2023年3月13日-16日, 立教大学, 東京

レポート番号: S2-004

第4回「あかり」国際会議 (2017年10月17-20日. 東京大学), 文京区, 東京形態: カラー図版あり資料番号: AA1730026036レポート番号: JAXA-SP-17-009E 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, JapanWe analyzed the 4.67 micrometers CO ro-vibrational absorption band in nearby ten active galactic nuclei (AGNs) observed with AKARI and Spitzer by fitting a plane-parallel local thermal equilibrium gas model. We found that the CO gas is warm (200-500 K) with a large column density (N(sub H) less than in the order of 10(exp 23) cm-2). Such a large column of warm gas is not achievable with UV heating or shock heating in starbursts. The most convincing heating source is X-ray photons emitted from the nuclei, which can produce warm gas of N(sub H) in the order of 10(exp 24) cm-2. This indicates that the region probed by the CO absorption is in the vicinity of the nuclei. The hydrogen column density estimated from the CO band is smaller than that inferred from X-ray observations. The observed deep absorption implies that the gas is close to the continuum source. We suggest that the probed region is outside the X-ray emitting region and just in front of the dust sublimation layer, which can be designated as the inner rim of the obscuring material around the AGNs.Physical characteristics: Original contains color illustrations

形態: カラー図版あり資料番号: AA1730027026レポート番号: JAXA-SP-17-010E SPICA Science Conference from Exoplanets to Distant Galaxies: SPICA's New Window on the Cool Universe (June 18-21, 2013. Ito Hall, the University of Tokyo), Bunkyou-ku, Tokyo, JapanWe carried out systematic observations of the HI recombination line Bra (4.05 μm) in nearby (z less than 0.3) ultraluminous infrared galaxies (ULIRGs), using AKARI near-infrared 2.5-5.0 μm spectroscopy. We derived star formation rates (SFRs) from the Bra line, whose observed flux is predicted to be the highest among HI recombination lines in conditions with large dust extinction (visual extinction Av greater than 15 mag) expected in ULIRGs. Using the 3.3 μm polycyclic aromatic hydrocarbon emission in addition to the Bra line as an indicator of the SFR, we estimated the contribution of the star formation to the total infrared luminosity in 51 ULIRGs. The contribution was on average 28 plus or minus4 0/o in ULIRGs optically classified as H II, while 14 plus or minus2 0/o in ULIRGs optically classified as LINER or Seyfert. This result indicates that the star formation is significantly active in H II ULIRGs and other energy source, i.e. active galactic nuclei, is needed in LINER ULIRGs.Physical characteristics: Original contains color illustrations

第4回「あかり」国際会議 (2017年10月17-20日. 東京大学), 文京区, 東京形態: カラー図版あり資料番号: AA1730026077レポート番号: JAXA-SP-17-009E 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, JapanWe 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.Physical characteristics: Original contains color illustrations

第4回「あかり」国際会議 (2017年10月17-20日. 東京大学), 文京区, 東京形態: カラー図版あり資料番号: AA1730026063レポート番号: JAXA-SP-17-009E