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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.
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.
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.