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SURVEY OF DUSTY ACTIVE GALACTIC NUCLEI BASED ON THE MID-INFRARED ALL-SKY SURVEY CATALOG
Oyabu, S.,Ishihara, D.,Yamada, R.,Kaneda, H.,Yamagishi, M.,Toba, Y.,Matsuhara, H.,Nakagawa, T.,Malkan, M.,Shirahata, M. The Korean Astronomical Society 2012 天文學論叢 Vol.27 No.4
Many observations have found evidence of the presence of a large number of heavily obscured Active Galactic Nuclei (AGNs). However, the nature of this population is only poorly understood because heavy obscuration by dust prevents one from finding them at optical wavelengths. Mid-infrared AGN searches can overcome this obstacle by penetrating through dust and by detecting direct emission from the dust torus. Thus, we can identify most of the AGN population, including type-2 and buried AGNs. Using the AKARI mid-infrared all-sky survey, we performed an AGN search in the nearby universe. Utilizing the 2MASS photometry, we selected mid-infrared-excess sources and carried out near-infrared spectroscopic observations in the AKARI Phase 3. During these follow-up observations, we have found three galaxies that show strong near-infrared red continuum from hot dust with a temperature of about 500 K, but do not show any AGN features in other wavelengths. The most suitable explanation of near-infrared continuum is the presence of central AGNs. Therefore, we conclude that they are AGNs obscured by dust. We performed X-ray observations of the two galaxies with SUZAKU. No detections in the 0.4-10 keV suggest that the column density may be much higher than $N_H=10^{23.5}cm^{-2}$. Comparing the masses of the host galaxies with those of the SDSS AGNs, we find that the host galaxies of the dusty AGNs discovered with AKARI are less massive populations than those of optically selected AGNs.
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.
Yamada, R.,Oyabu, S.,Kaneda, H.,Yamagishi, M.,Ishihara, D.,Kim, J.H.,Im, M.,Toba, Y.,Matsuhara, H. The Korean Astronomical Society 2012 天文學論叢 Vol.27 No.4
We investigate the relation between star formation activity and PAH $3.3{\mu}m$ emission. Our targets are mid-infrared-excess galaxies selected from the AKARI all-sky survey point source catalog. We performed AKARI near-infrared spectroscopy for them. As a result, we obtained $2.5-5{\mu}m$spectra of 79 galaxies, and selected 35 star-forming galaxies out of them. Comparing the PAH $3.3{\mu}m$ luminosities with the infrared luminosities, we find a linear correlation between them. However, by adding the results from literatures for luminous infrared galaxies and ultra-luminous infrared galaxies that are more luminous than our sample, the ratio of the PAH to the infrared luminosity is found to decrease towards the luminous end.
Pen, B.,Oyabu, T.,Hidaka, S.,Hidari, H. Asian Australasian Association of Animal Productio 2005 Animal Bioscience Vol.18 No.4
Ten 18.5-month old Holstein steers were allocated into two diet groups of five and fed either concentrates as control group or potato by-products based silage (PBS) as experimental group for six months to investigate the effect of PBS on growth performance, carcass characteristics and fatty acid composition of carcass fats. The PBS diet consisted, in a DM basis, of 74.5% PBS, 16% hay, and 9.5% soybean milk residue (SMR). The control diet consisted, in a DM basis, of 82.5% concentrates and 17.5% hay. There were no significant differences in the overall average daily gain (ADG), dry matter intake (DMI), feed efficiency, yield score and meat quality score of dressed carcass between the two diet groups. There were no statistical differences in DM, crude protein (CP), and ether extract (EE) of beef and melting point of all adipose tissues from steers fed both diets. The PBS-fed steers tended to have lower Warner Bratzler shear (WBS) values than in the concentrate-fed steers (13.0 vs. 17.7 lb, p<0.1). At both sampling times 3 and 6 months of feeding period, PBS-fed steers had higher proportions of polyunsaturated fatty acids (PUFA), especially linoleic (C18:2) acids in subcutaneous fat than in control group (p<0.05). PBS-fed steers had significantly higher proportions of PUFA, especially C18:2 fatty acids than in concentrate-fed steers in carcass fats (p<0.05). In conclusion, feeding PBS to fattening steers has shown to have the same potential as concentrate feeding in terms of effect on the growth performance, feed efficiency, and carcass characteristics. Interestingly, PBS also seems preferable to concentrates because it increased the proportion of C18:2 fatty acid composition of carcass fats which is valuable for beef consumers.
PROPERTIES OF DUST IN EARLY-TYPE GALAXIES BASED ON THE ALL-SKY-SURVEY DATA AND NEAR-INFRARED SPECTRA
Mori, T.,Oyabu, S.,Kaneda, H.,Ishihara, D.,Yamagishi, M. The Korean Astronomical Society 2012 天文學論叢 Vol.27 No.4
We present the properties of dust and the near-infrared spectral features in nearby early-type galaxies. The properties of dust are obtained from the AKARI far-infrared all-sky survey diffuse map. The AKARI/IRC is used for the near-infrared spectra. We improve spectral data with the new dark subtraction method on the basis of the knowledge acquired in our laboratory experiments of the engineering-model detector for the IRC. We have succeeded in fitting the continuum by a power-law function and detecting CO and SiO absorption features in early-type galaxy spectra. Comparing the properties of dust and near-infrared spectral features, we find that the power-law slope depends on dust temperature, but not on the dust mass, which suggests that low-luminosity AGNs may contribute to the changes in the power-law slope and dust temperature.
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.
SYSTEMATIC STUDY OF INTERSTELLAR ICES IN NEARBY GALAXIES
Yamagishi, M.,Kaneda, H.,Oyabu, S.,Ishihara, D.,Onaka, T.,Shimonishi, T.,Suzuki, T. The Korean Astronomical Society 2012 天文學論叢 Vol.27 No.4
The absorption features due to interstellar ices, especially $H_2O$ and $CO_2$ ices, provide us with crucial information on present and past interstellar environments, and thus the evolutionary histories of galaxies. Before AKARI, however, few detections of ices were reported for nearby galaxies. The AKARI's unique capability of near-infrared spectroscopy with high sensitivity enables us to systematically study ices in nearby galaxies. Thus we have explored many near-infrared spectra ($2.5-5{\mu}m$) of the 211 pointed observations, searching for the absorption features of ices. As a result, out of 122 nearby galaxies, we have significantly detected $H_2O$ ice from 36 galaxies and $CO_2$ ice from 9 galaxies. It is notable that the ices are detected not only in late-type galaxies but also in early-type galaxies. We find that $CO_2$ ice is more compactly distributed near the galactic center than $H_2O$ ice. Finally, we suggest that the gas density of a molecular cloud and UV radiation may be important factors to determine the abundance of ices.
NEAR-INFRARED HIGH-RESOLUTION SPECTROSCOPY OF THE OBSCURED AGN IRAS 01250+2832
Shirahata, M.,Usuda, T.,Oyabu, S.,Nakagawa, T.,Yamamura, I. The Korean Astronomical Society 2012 天文學論叢 Vol.27 No.4
We provide a new physical insight on the hot molecular clouds near the nucleus of the heavily obscured AGN IRAS 01250+2832, based on the results of near-infrared high-resolution spectroscopy of gaseous CO ro-vibrational absorption lines with Subaru/IRCS. The detected CO absorption lines up to highly excited rotational levels reveal that hot dense molecular clouds exist around the AGN under the peculiar physical conditions.
THE CENTRAL REGION OF THE BARRED SPIRAL GALAXY NGC 1097 PROBED BY AKARI NEAR-INFRARED SPECTROSCOPY
Kondo, T.,Kaneda, H.,Oyabu, S.,Ishihara, D.,Mori, T.,Yamagishi, M.,Onaka, T.,Sakon, I.,Suzuki, T. The Korean Astronomical Society 2012 天文學論叢 Vol.27 No.4
With AKARI, we carried out near-infrared spectroscopy of the nearby barred spiral galaxy, NGC 1097, categorized as Seyfert 1 with a circumnuclear starburst ring. Our observations mapped the galactic center region. As a result, we obtain the spatial distributions of the polycyclic aromatic hydrocarbon $3.3{\mu}m$ and the aliphatic hydrocarbon $3.4-3.6{\mu}m$ emission. The former is detected from all the observed regions and the latter is enhanced near the bar connecting the ring with the nucleus. In addition, we detect absorption features due to $H_2O$ ice and CO/SiO at the ring and the galactic center, while we detect the hydrogen recombination line $Br{\alpha}$ only from the ring. Hence the observed spectra change dramatically within the central 1 kpc region.