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RISS 인기검색어
- 검색키워드
- 저자 : Tomonori Usuda (검색결과 2 건)
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HIGHLY EXCITED CO LINES IN ACTIVE GALAXIES BOTH IN ABSORPTION AND IN EMISSION
TAKAO NAKAGAWA,Mai Shirahata,Tomonori Usuda 한국천문학회 2017 天文學論叢 Vol.32 No.1
In order to reveal physical conditions of molecular gas in active galaxies(“active galaxies” mean both starbursts and AGNs in this paper),we carried out systematic observations(R = 19 ~ 120) of CO fundamental band at 4.7 $\mu$m in absorption with\textit{AKARI}. We also made follow-upCO absorption observations at higher spectral resolution (R = 5000 ~ 1000) with \textit{Subaru}. Recently, \textit{Herschel}made extensive observations of highly-excited CO lines in emission in the far-infrared. The two datasets (absorption and emission) sometimes provide us with apparently inconsistent results. One case is starburst galaxies:\textit{Subaru} observations showed low temperature of molecular gas toward the starburstNGC253, while \textit{Herschel} detected highly excited CO lines in the starburst. This suggests that warmmolecular clouds are more deeply embedded than newly formed star clusters. The other case is obscured AGNs;\textit{Herschel} detected highly excited CO lines in emission in nearby AGNs,while \textit{AKARI} and\textit{Subaru} observations showed CO absorptiononly in some of the obscured AGNs. This could reflect the difference of nature of molecular tori in these AGNs. We propose the combination of the absorption and emission observationsas an effective tool to reveal geometry of warm molecular clouds in activegalaxies.
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NEAR-INFRARED SPECTROSCOPY OF CO RO-VIBRATIONAL ABSORPTION TOWARD HEAVILY OBSCURED AGNs
MAI SHIRAHATA,TAKAONAKAGAWA,SHINKI OYABU,Tomonori Usuda 한국천문학회 2017 天文學論叢 Vol.32 No.1
We provide a new physical insight on the hot molecular clouds near the nucleus of the obscured AGNs. We performed near-infrared spectroscopic observations of heavily obscured AGNsin order to reveal physical characteristics of molecular clouds,especially focused on the CO fundamental ro-vibrational absorption around 4.7 $\rm{\mu m}$. We have made systematic moderate-resolution spectroscopic observations toward 30 representative (U)LIRGsusing the {\it AKARI}/IRC, and some of the ULIRGs showed the strong CO absorption feature. For three bright (U)LIRGs that show a steep red continuum with the deep CO absorption feature,IRAS~08572$+$3915, UGC~05101, and IRAS~01250$+$2832, we have also made high-resolutionspectroscopic observations using the Subaru/IRCS. We have successfully detected many absorption linesup to highly excited rotational levels, and these lines are very deep and extremely broad. The derived physical conditions of molecular clouds are extreme; the gas temperatureis as high as several~100 to a 1000 K, the H$_2$ column density is larger than 10$^{22}$ $\rm{cm^{-2}}$,and the gas density is greater than 10$^7$ $\rm{cm^{-3}}$. Such hot and dense molecular cloudsmust exist around the central engine of the AGN.
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