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AKARI OBSERVATIONS OF DUSTY TORI OF ACTIVE GALACTIC NUCLEI
SHINKI OYABU,HIDEHIRO KANEDA,Masaya Izuhara,Keisuke Tomita,DAISUKE ISHIHARA,Kimiaki Kawara,Yoshiki Matsuoka 한국천문학회 2017 天文學論叢 Vol.32 No.1
The dusty torus of Active Galactic Nuclei (AGNs) is one of theimportant components for theunification theory of AGNs. The geometry and properties ofthe dusty torus are key factors in understanding the nature of AGNs aswell as the formation and evolution of AGNs. However, they are stillunder discussion. Infrared observation is useful for understanding the dustytorus as thermal emission from hot dust with the dust sublimationtemperature ($\sim$ 1500 K) has been observed in the infrared. We have analyzed infrared spectroscopic data of low-redshift andhigh-redshift quasars, which are luminous AGNs. For the low-redshift quasars, we constructed the spectral energydistributions (SEDs) with AKARI near-infrared and Spitzer mid-infraredspectra and decomposed the SEDs into a power-lawcomponent from the nuclei, silicate features, and blackbody components withdifferent temperatures from the dusty torus. From the decomposition,the temperature of the innermost dusty torus shows the range between900-2000 K. For the high-redshiftquasars, AKARI traced rest-frameoptical and near-infrared spectra of AGNs. Combining with WISE data,we havefound that the temperature of the innermost dusty torus in high redshift quasarsis lower than that in typical quasars. The hydrogen H$\alpha$ emission line from the braod emission line region in thequasars also shows narrow full widthat half maximumof 3000$-$4000 km s$^{-1}$. These results indicatethat the dusty torus and the broad emission line region are more extendedthan those of typical quasars.
THE 18 ㎛ LUMINOSITY FUNCTION OF GALAXIES WITH AKARI
Toba, Yoshiki,Oyabu, Shinki,Matsuhara, Hideo,Ishihara, Daisuke,Malkan, Matt,Wada, Takehiko,Ohyama, Youichi,Kataza, Hirokazu,Takita, Satoshi The Korean Astronomical Society 2012 天文學論叢 Vol.27 No.4
We present the $18{\mu}m$ luminosity function (LF) of galaxies at 0.006 < z < 0.8 (the average redshift is ~ 0.04) using the AKARI mid-infrared All-Sky Survey catalogue. We have selected 243 galaxies at $18{\mu}m$ from the Sloan Digital Sky Survey (SDSS) spectroscopic region. These galaxies then have been classified into five types; Seyfert 1 galaxies (Sy1, including quasars), Seyfert 2 galaxies (Sy2), low ionization narrow emission line galaxies (LINER), galaxies that are likely to contain both star formation and Active Galactic Nuclei (AGN) activities (composites), and star forming galaxies (SF) using optical emission lines such as the line width of $H{\alpha}$ or the emission line ratios of [OIII]/$H{\beta}$ and [NII]/$H{\alpha}$. As a result of constructing the LF of Sy1 and Sy2, we found the following results; (i) the number density ratio of Sy2 to Sy1 is $1.64{\pm}0.37$, larger than the results obtained from optical LF and (ii) the fraction of Sy2 in the entire AGN population may decrease with $18{\mu}m$ luminosity. These results suggest that most of the AGNs in the local universe are obscured by dust and the torus structure probably depends on the mid-infrared luminosity.
Yoshiki Toba,SHINKI OYABU,Hideo Matsuhara,DAISUKE ISHIHARA,Matt A. Malkan,Takehiko Wada,YOUICHI OHYAMA,Hirokazu Kataza,SATOSHI TAKITA,Chisato Yamauchi 한국천문학회 2017 天文學論叢 Vol.32 No.1
We demonstrate the luminosity dependence of the covering factor (CF) of active galactic nuclei (AGNs), based on AKARI mid-infrared all-sky survey catalog. Combining the AKARI with Sloan Digital Sky Survey (SDSS) spectroscopic data, we selected 243 galaxies at 9 $\mu$m and 255 galaxies at 18 $\mu$m. We then identified 64 AGNs at 9 $\mu$m and 105 AGNs at 18 $\mu$m by their optical emission lines. Following that, we estimated the CF as the fraction of type 2 AGN in all AGNs. We found that the CF decreased with increasing 18 $\mu$m luminosity, regardless of the choice of type2 AGN classification criteria.
LABORATORY EXPERIMENTS OF OFF-AXIS MIRROR OPTICS OF ALUMINUM FOR SPACE INFRARED MISSIONS
Shinji Oseki,SHINKI OYABU,DAISUKE ISHIHARA,Keigo Enya,Kanae Haze,Takayuki Kotani,HIDEHIRO KANEDA,Miho Nishiyama,Lyu Abe,Tomoyasu Yamamuro 한국천문학회 2017 天文學論叢 Vol.32 No.1
We report our research on aluminum mirror optics for future infrared astronomical satellites. For space infrared missions, cooling the whole instrument is crucial to suppress the infrared background and detector noise. In this aspect, aluminum is appropriate for cryogenic optics, because the same material can be used for the whole structure of the instrument including optical components thanks to its excellent machinability, which helps to mitigate optical misalignment at low temperatures. We have fabricated aluminum mirrors with ultra-precision machining and measured the wave front errors (WFEs) of the mirrors with a Fizeau interferometer. Based on the power spectral densities of the WFEs, we confirmed that the surface accuracy of all the mirrors satisfied the requirements for the SPICA Coronagraph Instrument. We then integrated the mirrors into an optical system, and examined the image quality of the system with an optical laser. As a result, the total WFE is estimated to be 33 nm (rms) from the Strehl ratio. This is consistent with the WFEs estimated from the measurement of the individual mirrors.
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.
Misaki Hanaoka,HIDEHIRO KANEDA,SHINKI OYABU,Yasuki Hattori,Kotomi Tanaka,Sota Ukai,Kazuyuki Shichi,Takehiko Wada,Toyoaki Suzuki,Kentaroh Watanabe,Koichi Nagase,Shunsuke Baba,Chihiro Kochi 한국천문학회 2017 天文學論叢 Vol.32 No.1
To realize large-format compact array detectors covering a wide far-infrared wavelength range up to 200 $\mu$m, we have been developing Blocked-Impurity-Band (BIB) type Ge detectors with the room-temperature surface-activated wafer bonding technology provided by Mitsubishi Heavy Industries. We fabricated various types of $p^+$-$i$ junction devices which possessed a BIB-type structure, and evaluated their spectral response curves using a Fourier transform spectrometer. From the Hall effect measurement, we also obtained the physical characteristics of the $p^+$ layers which constituted the $p^+$-$i$ junction devices. The overall result of our measurement shows that the $p^+$-$i$ junction devices have a promising applicability as a new far-infrared detector to cover a wavelength range of 100--200 μm.
STUDY OF CO2/H2O ICE ABUNDANCE RATIOS IN NEARBY GALAXIES WITH THE AKARI NEAR-INFRARED SPECTROSCOPY
MITSUYOSHI YAMAGISHI,HIDEHIRO KANEDA,SHINKI OYABU,DAISUKE ISHIHARA,TAKASHI ONAKA,TAKASHI SHIMONISHI,Toyoaki Suzuki 한국천문학회 2017 天文學論叢 Vol.32 No.1
We study $\mathrm{CO_2/H_2O}$ ice abundance ratios in nearby galaxies using $AKARI$ near-infrared slit spectroscopy. Past studies of the ices intensively examined $\mathrm{CO_2/H_2O}$ ratios mainly in our Galaxy, and found that there were considerable variations in the $\mathrm{CO_2/H_2O}$ ratios from object to object. The cause of the variations is, however, still under debate. As a result of the analysis of our sample that includes 1031 regions in 158 galaxies, the $\mathrm{CO_2/H_2O}$ ratios are in a range of 0.05--0.30. In the dataset, we find that the $\mathrm{CO_2/H_2O}$ ratios positively correlate with the Br$\alpha$/PAH 3.3 $\mu$m ratios which reflect the massive star formation activity. Furthermore, we find that the $\mathrm{CO_2/H_2O}$ ratios positively correlate with the specific star formation rates of the galaxies where the ices are detected, that reflect the evolutionary stage of a galaxy. These results suggest that the $\mathrm{CO_2/H_2O}$ ratios are enhanced in active star-forming regions and young galaxies.
A SYSTEMATIC STUDY OF DUST IN EARLY-TYPE GALAXIES WITH AKARI
Takuma Kokusho,HIDEHIRO KANEDA,TORU KONDO,SHINKI OYABU,MITSUYOSHI YAMAGISHI,Katsuhiro Murata 한국천문학회 2017 天文學論叢 Vol.32 No.1
Early-type galaxies (ETGs) are generally dominated by old low-mass stars, which are not very productive of dust, and hot interstellar plasmas, which are very destructive of dust. Thus ETGs provide harsh environments for survival of dust. It has been found that some ETGs contain a large amount of dust, and yet its supply mechanism is not understood well. We present the result of a systematic study of dust in ETGs with the AKARI mid- and far-infrared all-sky surveys. From the AKARI result and the $Ks$ band data obtained by ground-based telescopes, we find that there is a global correlation between the dust mass and stellar luminosity. We also compare the AKARI all-sky survey result with the CO data to discuss origins of dust in ETGs.