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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>
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.
THE CURRENT STATUS OF THE AKARI MID-INFRARED ALL-SKY DIFFUSE MAPS
TOMOYA AMATSUTSU,DAISUKE ISHIHARA,TORU KONDO,HIDEHIRO KANEDA,SHINKI OYABU,MITSUYOSHI YAMAGISHI,KEICHIRO NAKAMICHI,Hidetoshi Sano,TAKASHI ONAKA 한국천문학회 2017 天文學論叢 Vol.32 No.1
We are creating all-sky diffuse maps from the AKARI mid-infrared survey datawith the two photometric bands centered at wavelengths of 9 and 18~$\micron$. The AKARI mid-infrared diffuse maps achieve higher spatial resolution and higher sensitivitythan the IRAS maps. In particular, the 9~$\micron$ data are unique resources as anall-sky tracer of the emission of polycyclic aromatic hydrocarbons (PAHs). However, the original data suffer many artifacts. Thus, we have been developing correction methods. Among them, we have recently improvedcorrection methods for the non-linearity and the reset anomaly of the detector response. These corrections successfully reduce the artifact level down to 0.1\,MJy sr$^{-1}$ on average,% reduce the intensity error from a $\sim 0.2 \ \mjysr$ level down to $\sim 0.1 \ \mjysr$,which is essential for discussion onfaint extended emission (e.g., the Galactic PAH emission). We have also made progress in the subtraction of the scattered lightcaused in the camera optics. We plan to release the improved diffuse maps to the public within a year.
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 $L_{\rm{IR}}$.
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.
Hidetoshi Sano,TOMOYA AMATSUTSU,TORU KONDO,KEICHIRO NAKAMICHI,MITSUYOSHI YAMAGISHI,DAISUKE ISHIHARA,SHINKI OYABU,HIDEHIRO KANEDA,KENGO TACHIHARA,YASUO FUKUI 한국천문학회 2017 天文學論叢 Vol.32 No.1
We present a comparative study of CO and polycyclic aromatic hydrocarbon (PAH) emission toward a region including the massive star-forming regions of NGC 6334 and NGC 6357. We use the NANTEN $^{12}$CO($J$=1--0) data and the $AKARI$ 9 $\mu$m All-Sky diffuse map in order to evaluate the calibration accuracy of the $AKARI$ data. We confirm that the overall CO distribution shows a good spatial correspondence with the PAH emission, and their intensities exhibit a good power-law correlation with a spatial resolution down to 4$\rq{}$ over the region of 10$^\circ$$\times$10$^\circ$. We also reveal poorer correlation for small scale structures between the two quantities toward NGC 6357, due to strong UV radiation from local sources. Larger scatter in the correlation toward NGC 6357 indicates higher ionization degree and/or PAH excitation than that of NGC 6334.