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AKARI INFRARED CAMERA SURVEY OF THE LARGE MAGELLANIC CLOUD
T. Shimonishi,D. KATO,Y. ITA,T.ONAKA 한국천문학회 2017 天文學論叢 Vol.32 No.1
We conducted an unbiased near- to mid-infrared imaging and spectroscopic survey of the Large Magellanic Cloud (LMC) as a part of the AKARI Mission Program ``Large-area Survey of the LMC'' (LSLMC, PI: T. Onaka). An area of about 10 square degrees of the LMC was observed by five photometric bands (3.2, 7, 11, 15, and 24 $\mu$m) and a low-resolution slitless prism (2 -- 5 $\mu$m, R $\sim$20) equipped with \textit{AKARI}/IRC. We constructed and publicly released photometric and spectroscopic catalogues of point sources in the LMC based on the survey data. The catalogues provide a large number of near-infrared spectral data, coupled with complementary broadband photometric data. Combined use of the present \textit{AKARI} LSLMC catalogues with other infrared point source catalogues of the LMC possesses scientific potential that can be applied to various astronomical studies.
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.
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 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.
Suzuki, T.,Kaneda, H.,Onaka, T. The Korean Astronomical Society 2012 天文學論叢 Vol.27 No.4
Nearby spiral galaxies M101 and M81 are considered to have undergone a galaxy-galaxy interaction. M101 has experienced HI gas infall due to the interaction. With AKARI far-infrared (IR) photometric observations, we found regions with enhanced star forming activity, which are spatially close to regions affected by the interaction. In addition, the relation between the star formation rate (SFR) and the gas content for such regions shows a significant difference from typical spiral arm regions. We discuss possible explanations for star formation processes on a kiloparsec scale and the association with interaction-triggered star formation. We also observed the compact group of galaxies Stephan's Quintet (SQ) with the AKARI Far-infrared Surveyor (FIS). The SQ shows diffuse intergalactic medium (IGM) due to multiple collisions between the member galaxies and the IGM. The intruder galaxy NGC 7318b is currently colliding with the IGM and causes a large-scale shock. The 160 micron image clearly shows the structure along the shock ridge as seen in warm molecular hydrogen line emission and X-ray emission. The far-IR emission from the shocked region comes from the luminous [CII]$158{\mu}m$ line and cold dust (~ 20 K) that coexist with molecular hydrogen gas. Survival of dust grains is indispensable to form molecular hydrogen gas within the collision age (~ 5 Myr). At the stage of the dusty IGM environment, [CII] and $H_2$ lines rather than X-ray emission are powerful cooling channels to release the collision energy.
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.
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.
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.
INFRARED COMPOSITION OF THE LARGE MAGELLANIC CLOUD
Siudek, M.,Pollo, A.,Takeuchi, T.T.,Ita, Y.,Kato, D.,Onaka, T. The Korean Astronomical Society 2012 天文學論叢 Vol.27 No.4
Understanding the birth and evolution of galaxies, and the history of star formation in them, is one of the most important problems in astronomy. Using the data from the AKARI IRC survey of the Large Magellanic Cloud at 3.2, 7, 11, 15, and $24{\mu}m$, we have constructed a multi-wavelength catalog containing data from the cross-correlation with a number of other databases at different wavelengths. We present the first approach with a Support Vector Machine (SVM)-based method to separate different classes of stars in LMC in the color-color and color-magnitude diagrams.