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PROPERTIES OF DUST IN VARIOUS ENVIRONMENTS OF NEARBY GALAXIES
HIDEHIRO KANEDA,Takuma Kokusho,Rika Yamada,DAISUKE ISHIHARA,SHINKI OYABU,TORU KONDO,MITSUYOSHI YAMAGISHI,Akiko Yasuda,TAKASHI ONAKA,Toyoaki Suzuki 한국천문학회 2017 天文學論叢 Vol.32 No.1
We have performed systematic studies of the properties of dust in various environments of nearby galaxies with AKARI. The unique capabilities of AKARI, such as near-infrared (near-IR) spectroscopy combined with all-sky coverage in the mid- and far-IR, enable us to study processing of dust, particularly carbonaceous grains includings polycyclic aromatic hydrocarbons (PAHs), for unbiased samples of nearby galaxies. In this paper, we first review our recent results on individual galaxies, highlighting the uniqueness of AKARI data for studies of nearby galaxies. Then we present results of our systematic studies on nearby starburst and early-type galaxies. From the former study based on the near-IR spectroscopy and mid-IR all-sky survey data, we find that the properties of PAHs change systematically from IR galaxies to ultra-luminous IR galaxies, depending on the IR luminosity of a galaxy or galaxy population. From the latter study based on the mid- and far-IR all-sky survey data, we find that there is a global correlation between the amounts of dust and old stars in early-type galaxies, giving an observational constraint on the origin of the dust.
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.
Yamagishi, Mitsuyoshi,Kaneda, Hidehiro,Ishihara, Daisuke,Oyabu, Shinki,Onaka, Takashi,Shimonishi, Takashi,Suzuki, Toyoaki,Minh, Young Chol IOP Publishing 2013 ASTROPHYSICAL JOURNAL LETTERS - Vol.773 No.2
<P>With AKARI, we obtain the spatially resolved near-infrared (NIR) (2.5-5.0 mu m) spectra for the nearby starburst galaxy M 82. These spectra clearly show absorption features due to interstellar ices. Based on the spectra, we created the column density maps of H2O and CO2 ices. As a result, we find that the spatial distribution of H2O ice is significantly different from that of CO2 ice; H2O ice is widely distributed, while CO2 ice is concentrated near the galactic center. Our result reveals for the first time variations in CO2/H2O ice abundance ratio on a galactic scale, suggesting that an ice-forming interstellar environment changes within a galaxy. We discuss the cause of the spatial variations in the ice abundance ratio, utilizing spectral information on the hydrogen recombination Br alpha and Br beta lines and the polycyclic aromatic hydrocarbon 3.3 mu m emission appearing in the AKARI NIR spectra.</P>
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.
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.
DEVELOPMENT OF A CRYOGENIC TESTING SYSTEM FOR MID-INFRARED DETECTORS ON SPICA
Miho Nishiyama,Hidehiro Kaneda,Daisuke Ishihara,Shinji Oseki,Nami Takeuchi,Takahiro Nagayama,Takehiko Wada 한국천문학회 2017 天文學論叢 Vol.32 No.1
For future space IR missions, such as SPICA, it is crucial to establish an experimental method for evaluating the performance of mid-IR detectors. In particular, the wavelength dependence of the sensitivity is important but difficult to be measured properly. We are now preparing a testing system for mid-IR Si:As/Si:Sb detectors on SPICA. We have designed a cryogenic optical system in which IR signal light from a pinhole is collimated, passed through an optical filter, and focused onto a detector. With this system, we can measure the photoresponse of the detector for various IR light using optical filters with different wavelength properties. We have fabricated aluminum mirrors which are adopted to minimize thermal distortion effects and evaluated the surface figure errors. The total wavefront error of the optical system is 1.3 μm RMS, which is small enough for the target wavelengths (20 - 37 μm) of SPICA. The point spread function measured at a room temperature is consistent with that predicted by the simulation. We report the optical performance of the system at cryogenic temperatures.
AKARI OBSERVATIONS OF MASSIVE STAR-FORMING REGIONS INDICATIVE OF LARGE-SCALE CLOUD-CLOUD COLLISIONS
Yasuki Hattori,HIDEHIRO KANEDA,DAISUKE ISHIHARA,MITSUYOSHI YAMAGISHI,TORU KONDO,Hidetoshi Sano 한국천문학회 2017 天文學論叢 Vol.32 No.1
We present our AKARI study of massive star forming regions where a large-scale cloud-cloud collision possibly contributes to massive star formation. Our targets are Spitzer bubbles, which consist of two types of bubbles, closed and broken ones; the latter is a candidate of the objects created by cloud-cloud collisions. We performed mid- and far-infrared surface photometry toward Spitzer bubbles to obtain the relationship between the total infrared luminosity, $L_{\rm{IR}}$, and the bubble radius, $R$. As a result, we find that $L_{\rm{IR}}$ is roughly proportional to ${R}^\beta$ where ${\beta}=2.1{\pm}0.4$. Broken bubbles tend to have larger radii than closed bubbles for the same $L_{\rm{IR}}$.
DEVELOPMENT OF NEW STITCHING INTERFEROMETRY FOR THE SPICA TELESCOPE
Asa Yamanaka,HIDEHIRO KANEDA,MITSUYOSHI YAMAGISHI,TORU KONDO,Takuma Kokusho,Kotomi Tanaka,Misaki Hanaoka,TAKAO NAKAGAWA,Mitsunobu Kawada,Naoki Isobe,Toshiaki Arai,TAKASHI ONAKA 한국천문학회 2017 天文學論叢 Vol.32 No.1
The telescope to be onboard SPICA (Space Infrared Telescope for Cosmology and Astrophysics) has an aperture diameter of 2.5 m and its imaging performance is to be diffraction-limited at a wavelength of 20 μm at the operating temperature of < 8 K. Because manufacturing precise autocollimating flat mirrors (ACFs) with sizes comparable to the SPICA telescope is not technically feasible, we plan to use sub-aperture stitching interferometry through ACFs for optical testing of the telescope. We have verified the applicability of the sub-aperture stitching technique to the SPICA telescope by performing stitching experiments in a vacuum at a room temperature, using the 800-mm telescope and a 300-mm ACF. We have also developed a new method to reduce uncertainties possibly caused by cryogenic and gravitational deformations of ACFs.
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.