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Mori, T.I.,Sakon, I.,Onaka, T.,Umehata, H.,Kaneda, H.,Ohsawa, R. The Korean Astronomical Society 2012 天文學論叢 Vol.27 No.4
We present the results of the near-infrared (NIR) to mid-infrared (MIR) slit spectroscopic observations of the diffuse emission toward nine positions in the nearby irregular galaxy Large Magellanic Cloud (LMC) with the Infrared Camera (IRC) on board AKARI. The unique characteristic of AKARI/IRC provides a great opportunity to analyze variations in the unidentified infrared (UIR) bands based on continuous spectra from 2.5 to $13.4{\mu}m$ of the same slit area. The observed variation of $I_{3.3}/I_{11.3}$ suggests destruction of small-sized UIR band carriers, polycyclic aromatic hydrocarbons (PAHs) in harsh environments. This result demonstrates that the UIR $3.3{\mu}m$ band provides us powerful information on the excitation conditions and/or the size distribution of PAHs, which is of importance for understanding the evolutionary process of hydrocarbon grains in the Universe. It also suggests a new diagnostic diagram of two band ratios, such as $I_{3.3}/I_{11.3}$ versus $I_{7.7}/I_{11.3}$, for the interstellar radiation conditions. We discuss on the applicability of the diagnostic diagram to other astronomical objects, comparing the LMC results with those observed in other galaxies such as NGC 6946, NGC 1313, and M51.
AKARI MID- TO FAR-INFRARED OBSERVATIONS OF DIFFUSE GALACTIC EMISSION
Sakon, I.,Onaka, T.,Mori, T.I.,Ohsawa, R.,Doi, Y.,Okada, Y.,Kaneda, H.,Ootsubo, T. The Korean Astronomical Society 2012 天文學論叢 Vol.27 No.4
We have collected dozens of mid-infrared spectra showing UIR bands from diffuse Galactic emitting regions with the AKARI's Infrared Camera (IRC) onboard AKARI, as part of the ISMGN Mission Program. The datasets cover various directions in the inner Galactic Plane ($|l|$ < 70 deg), in the outer Galactic Plane ($|l|$ > 70 deg), and in the off-Plane ($|b|$ > 2 deg). The variations in the UIR band ratios are examined in terms of the radiation environments judged from the far-infrared ($50-170{\mu}m$) spectral energy distribution (SED) made with AKARI/FIS All Sky Survey data at each slit position where mid-IR spectra were obtained. We have found that the band ratios of $6.2{\mu}m/11.2{\mu}m$ and $7.7{\mu}m/11.2{\mu}m$ toward the inner Galaxy are systematically higher than those toward the outer Galaxy and off the Galactic plane. Likely causes of the variations in properties of UIR bands in diffuse emission on a Galactic scale are discussed in this paper.
INVESTIGATION OF PAHs IN GALACTIC PLANETARY NEBULAE WITH THE AKARI/IRC AND THE SPITZER/IRS
Ohsawa, R.,Onaka, T.,Sakon, I.,Mori, T.I.,Yamamura, I.,Matsuura, M.,Kaneda, H.,Bernard-Salas, J.,Berne, O.,Joblin, C. The Korean Astronomical Society 2012 天文學論叢 Vol.27 No.4
Polycyclic aromatic hydrocarbons (PAHs) in Galactic planetary nebulae (PNe) are investigated by means of the unidentified infrared (UIR) bands. Continuous near- to mid-infrared spectra of PNe are obtained with the AKARI/IRC and the Spitzer/IRS. All 19 PNe in the present study show prominent dust emissions and we investigate the variation in the intensity ratios among the UIR bands. The ionization fraction and the size distribution of PAHs in PNe are derived using the UIR band ratios. We find that the ionization fraction of PAHs in PNe is around 0.0-0.6 and that small PAHs are scarce. The present result indicates a systematic trend of the $3.4{\mu}m$ aliphatic feature to become weak as the PAH ionization fraction increases.
ICE ABSORPTION FEATURES IN NIR SPECTRA OF GALACTIC OBJECTS
TAMAMI I. MORI,TAKASHI ONAKA,ITSUKI SAKON,RYOU OHSAWA,HIDEHIRO KANEDA,MITSUYOSHI YAMAGISHI,YOKO OKADA,MASAHIRO TANAKA,TAKASHI SHIMONISHI 한국천문학회 2017 天文學論叢 Vol.32 No.1
We present results of AKARI/IRC near-infrared (NIR) slit-spectroscopy (2.5--5.0\,$\mu$m, $R \sim 100$) of Galactic sources,focusing on ice absorption features. We investigate the abundance of H$_2$O and CO$_2$ ices and other ice species (CO and XCN ices)along lines of sight towards Galactic \ion{H}{ii} regions, massive YSOs, and infrared diffuse sources. Even among those different kinds of astronomical objects,the abundance ratio of CO$_2$ to H$_2$O ices does not vary significantly,suggesting that the pathway to CO$_2$ ice formation driven by UV irradiation is not effectiveat least among the present targets.
INTERSTELLAR DUST IN M51 FROM IRC IMAGES
Egusa, Fumi,Sakon, I.,Onaka, T.,Matsuhara, H.,Arimatsu, K.,Suzuki, T.,Wada, T.,The IRC team, The IRC team The Korean Astronomical Society 2012 天文學論叢 Vol.27 No.4
We present the IRC images of M51, a pair of interacting galaxies. Given the high angular resolution (7.4") and the wide field of view (~ 10') covering almost the entire M51 system, we investigate dust properties and their connection to the spiral arm structure. We have applied image-filtering processes including the wavelet analysis to the N3 image, which traces the total stellar mass best among the IRC bands. From this filtered image, the center, arm, and interarm regions are defined. A color, or flux ratio among the MIR bands, has been measured at each pixel (3.7" in size). We find a wide variety of S7/S11 with a difference between arm and interarm regions. We also find that at some positions S11 seems to be higher than predicted by MW dust models. Estimated contributions from the stellar continuum and gas emission lines to the band are not enough to explain this discrepancy. From these results, we deduce that the PAH ionization condition and its fraction to the total dust mass in M51 are different from those in MW.
NEAR-INFRARED PAH FEATURES IN GALACTIC PLANETARY NEBULAE
R. Ohsawa,O.ONAKA,I.SAKON,T.I. MORI,H.KANEDA,M.MATSUURA 한국천문학회 2017 天文學論叢 Vol.32 No.1
Polycyclic aromatic hydrocarbons (PAHs) are considered to be carriers of the unidentified infrared bands, which are ubiquitously observed in the Universe. PAHs are mainly formed around evolved carbon-rich stars and injected into interstellar space. Planetary nebulae (PNe), a late stage of low- and intermediate stellar mass evolution, are suitable objects to investigate the formation and evolution of PAHs. The shortest PAH feature is located in 3.3$\,\mu$m, which is important to examine the excitation and size distribution of PAHs. While the number of samples had been limited before, the high sensitivity of \textit{AKARI}/IRC has drastically increased the number of samples. We obtained the 2--5$\,\mu$m spectra of Galactic PNe with \textit{AKARI}/IRC and compiled a near-infrared spectral catalog, containing 73 PNe. We investigate the detection rate and the evolution of the PAH features. The characteristics of the catalog are illustrated and the origin of the evolution of the PAH features is discussed.
PROCESSING OF INTERSTELLAR MEDIUM AS DIVULGED BY AKARI
TAKASHI ONAKA,TAMAMI I. MORI,RYOU OHSAWA,ITSUKI SAKON,AARON C. BELL,MARK HAMMONDS,TAKASHI SHIMONISHI,DAISUKE ISHIHARA,HIDEHIRO KANEDA,YOKO OKADA,MASAHIRO TANAKA 한국천문학회 2017 天文學論叢 Vol.32 No.1
A wide spectral coverage from near-infrared (NIR) to far-infrared (FIR) of {\it AKARI} both for imaging and spectroscopy enablesus to efficiently study the emission from gas and dust in the interstellar medium (ISM). In particular, the Infrared Camera(IRC) onboard {\it AKARI}offers a unique opportunity to carry out sensitive spectroscopy in the NIR (2--5\,$\mu$m) for the first time from a spaceborn telescope. This spectral range contains a number of important dust bands and gas lines, such as the aromatic and aliphatic emissionbands at 3.3 and 3.4--3.5\,$\mu$m, H$_2$O and CO$_2$ ices at 3.0 and 4.3\,$\mu$m, CO, H$_2$, and \ion{H}{I} gas emission lines. In this paper we concentrate on the aromatic and aliphatic emission and ice absorption features. The balance between dust supply and destruction suggests significant dust processing takingplace as well as dust formation in the ISM. Detailed analysis of the aromatic and aliphatic bands of {\it AKARI} observations for a number of\ion{H}{ii} regions and \ion{H}{ii} region-like objectssuggests processing of carbonaceous dust in the ISM. The ice formation process canalso be studied with IRC NIR spectroscopy efficiently. In this review, dust processing in the ISM divulged by recentanalysis of {\it AKARI} data is discussed.
AKARI INFRARED OBSERVATIONS OF EMBEDDED YSOs IN THE MAGELLANIC CLOUDS
Shimonishi, T.,Onaka, T.,Kato, D.,Sakon, I.,Ita, Y.,Kawamura, A.,Kaneda, H. The Korean Astronomical Society 2012 天文學論叢 Vol.27 No.4
Spectroscopic studies of extragalactic YSOs have shown a great progress in the last few years. Infrared observations with AKARI made significant contributions to that progress. In this proceeding, we are going to introduce our current research on the infrared observations of ices and dust around embedded YSOs in the Magellanic Clouds.
PROCESSING OF INTERSTELLAR DUST GRAINS IN GALAXIES
Kaneda, H.,Ishihara, D.,Onaka, T.,Sakon, I.,Suzuki, T.,Kobata, K.,Kondo, T.,Yamagishi, M.,Yasuda, A. The Korean Astronomical Society 2012 天文學論叢 Vol.27 No.4
We have performed a systematic study of interstellar dust grains in various environments of galaxies. AKARI has revealed the detailed properties of dust grains not only in star-forming regions but also in regions not relevant to star formation, some of which are found not to follow our old empirical knowledge. Because of its unique capabilities, AKARI has provided new knowledge on the processing of large grains and polycyclic aromatic hydrocarbons (PAHs). For example, we detect PAHs from elliptical galaxies, which show unusual spectral features and spatial distributions, demonstrating importance of material processing in the interstellar space. We find that copious amounts of large grains and PAHs are flowing out of starburst galaxies by galactic superwinds, which are being shattered and destroyed in galactic haloes. We discover evidence for graphitization of carbonaceous grains near the center of our Galaxy, providing a clue to understanding the activity of the Galactic center. We review the results obtained from our AKARI program, focusing on the processing of carbonaceous grains in various environments of galaxies.
Planck Collaboration, Planck Collaboration,Giard, M.,Berne, O.,Doi, Y.,Ishihara, D.,Joblin, Ch.,Kaneda, I.,Marshall, D.,Nakagawa, T.,Ohsawa, R.,Onaka, T.,Sakon, I.,Shibai, H.,Ysard, N. The Korean Astronomical Society 2012 天文學論叢 Vol.27 No.4
We show how the rotation emission from isolated interstellar Polycyclic Aromatic Hydrocarbons (PAHs) can explain the so-called anomalous microwave emission (AME). AME has been discovered in the last decade as microwave interstellar emission (10 to 70 GHz) that is in excess compared to the classical emission processes: thermal dust, free-free and synchrotron. The PAHs are the interstellar planar nano-carbons responsible for the near infrared emission bands in the 3 to 15 micron range. Theoretical studies show that under the physical conditions of the interstellar medium (radiation and density) the PAHs adopt supra-thermal rotation velocities, and consequently they are responsible for emission in the microwave range. The first results from the PLANCK mission unexpectedly showed that the AME is not only emitted by specific galactic interstellar clouds, but it is present throughout the galactic plane, and is particularly strong in the cold molecular gas. The comparison of theory and observations shows that the measured emission is fully consistent with rotation emission from interstellar PAHs. We draw the main lines of our PLANCK-AKARI collaborative program which intends to progress on this question by direct comparison of the near infrared (AKARI) and microwave (PLANCK) emissions of the galactic plane.