• Journal of The Korean Astronomical Society
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• v.38 no.3
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• pp.365-370
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• 2005

We have made a multi-wavelength study of the X-ray bright giant shell complex 30 Doradus in the Large Magellanic Cloud (LMC). This is the one of the largest H II complexes in the Local Group. The Australia Telescope Compact Array (ATCA) and the Parkes 64-m single dish observations reveal that the distribution and internal motions of H I gas show the effects of fast stellar winds and supernova blasts. The hot emitting gas within the 30 Doradus complex and the entire giant H II complex are encompassed by an expanding H I shell. We investigate the dynamical age of this H I shell and compare to the age of starbursts occurred in the 30 Doradus nebula using the radiative transfer model and the infrared properties.

• Journal of The Korean Astronomical Society
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• v.38 no.4
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• pp.385-414
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• 2005

We have searched for infrared emission from supernova remnants (SNRs) included in the Spitzer Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) field. At the positions of 100 known SNRs, we made 3.6, 4.5, 5.8, and $8.0{\mu}m$ band images covering the radio continuum emitting area of each remnant. In-depth examinations of four band images based on the radio continuum images of SNRs result in the identification of sixteen infrared SNRs in the GLIMPSE field. Eight SNRs show distinct infrared emission in nearly all the four bands, and the other eight SNRs are visible in more than one band. We present four band images for all identified SNRs, and RGB-color images for the first eight SNRs. These images are the first high resolution (<2') images with comparative resolution of the radio continuum for SNRs detected in the mid-infrared region. The images typically show filamentary emission along the radio enhanced SNR boundaries. Most SNRs are well identified in the 4.5 and $5.8{\mu}m$ bands. We give a brief description of the infrared features of the identified SNRs.

• Publications of The Korean Astronomical Society
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• v.32 no.1
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• pp.105-107
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• 2017

We present results of AKARI/IRC near-infrared (NIR) slit-spectroscopy ($2.5-5.0{\mu}m$, R ~ 100) of Galactic sources, focusing on ice absorption features. We investigate the abundance of $H_2O$ and $CO_2$ ices and other ice species (CO and XCN ices) along lines of sight towards Galactic H $\small{II}$ regions, massive YSOs, and infrared diffuse sources. Even among those different kinds of astronomical objects, the abundance ratio of $CO_2$ to $H_2O$ ices does not vary significantly, suggesting that the pathway to $CO_2$ ice formation driven by UV irradiation is not effective at least among the present targets.

• Publications of The Korean Astronomical Society
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• v.32 no.1
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• pp.135-139
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• 2017

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 ultraluminous 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.

• Journal of The Korean Astronomical Society
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• v.32 no.1
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• pp.41-53
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• 1999

We have carried out high-resolution observations along one-dimensional cuts through the three Galactic super-shells GS 064-01-97, GS 090-28-17, and GS 174+02-64 in the HI 21 cm and CO J=l-0 lines. By comparing the HI data with IRAS data, we have derived the distributions of the $I_{100}$ and $T_{100}$ excesses, which are, respectively, the 100 ${\mu}m$ intensity and 100 ${\mu}m$ optical depth in excess of what would be expected from HI emission. We have found that both the $I_{100}$ and $T_{100}$ excesses have good correlations with the CO integrated intensity W co in all three supershells. But the $I_{100}$ excess appears to underestimate $H_2$ column density N($H_2$) by factors of 1.5-3.8. This factor is the ratio of atomic to molecular infrared emissivities, and we show that it can be roughly determined from the HI and IRAS data. By comparing the $T_{100}$ excess with $W_{co}$, we derive the conversion factor X $\equiv$ N ($H_2$) /$W_{co}{\simeq}$ 0.26 - 0.66 in the three supershells. In GS 090- 28-17, which is a very diffuse shell, our result suggests that the region with N($H_2$) $\le$ $3 {\times} 10^{20} cm^{-2}$ does not have observable CO emission, which appears to be consistent with previous results indicating that diffuse molecular gas is not observable in CO. Our results show that the molecular gas has a 60/100 ${\mu}m$ color temperature $T_d$ lower than the atomic gas. The low value of $T_d$ might be due either to the low equilibrium temperature or to the lower abundance of small grains, or a combination of both.

• Publications of The Korean Astronomical Society
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• v.27 no.4
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• pp.271-274
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• 2012

We present the result of systematic AKARI IRC infrared $2.5-5{\mu}m$ spectroscopy of >100 nearby luminous infrared galaxies, to investigate the energetic roles of starbursts and optically-elusive buried AGNs. Based on (1) the equivalent widths of the $3.3{\mu}m$ PAH emission features, (2) the optical depths of absorption features, and (3) continuum slopes, we can disentangle emission from starbursts and AGNs. We find that the energetic importance of buried AGNs increases with increasing galaxy infrared luminosities, suggesting that the AGN-starburst connections (and thereby possible AGN feedback to host galaxies) are luminosity dependent.

• Publications of The Korean Astronomical Society
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• v.27 no.4
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• pp.213-216
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• 2012

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.

• Journal of The Korean Astronomical Society
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• v.37 no.4
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• pp.285-288
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• 2004

Near-infrared imaging photometry supplemented by optical spectroscopy and narrow-band imaging of the H II region Sh 2-128 and its environment are presented. This region contains a developed H II region and the neighboring compact H II region S 128N associated with a pair of water maser sources. Midway between these, the core of a CO cloud is located. The principal ionizing source of Sh 2-128 is an 07 star close to its center. A new spectroscopic distance of 9.4 kpc is derived, very similar to the kinematic distance to the nebula. This implies a galactocentric distance of 13.5 kpc and z = 550 pc. The region is optically thin with abundances close to those predicted by galactocentric gradients. The $JHK_s$ images show that S 128N contains several infrared point sources and nebular emission knots with large near-infrared excesses. One of the three red Ks knots coincides with the compact H II region. A few of the infrared-excess objects are close to known mid- and far-infrared emission peaks. Star counts in J and $K_s$ show the presence of a small cluster of B-type stars, mainly associated with S 128N. The $JHK_s$ photometric properties together with the characteristics of the other objects in the vicinity suggest that Sh 2-128 and S 128N constitute a single complex formed from the same molecular cloud, with ages ${\~}10^6$ and < $3 {\times} 10^5$ years respectively. No molecular hydrogen emission was detected at 2.12 ${\mu}m$. The origin of this remote star forming region is an open problem.

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.89-91
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• 2015

Observed spectra of stars around the Sun have indicated that the Sun is located in a gas cavity, extending to 100pc. This gas cavity is called the "Local Bubble". The density of the interstellar medium (ISM) in the local bubble is about one tenth that of the average for the ISM in the Milky Way. Furthermore, some structures such as gas planes and strings in the local bubble are probably the result of supernovae. These, due to their low temperatures, can not be observed in the visible and infrared. The only way to do so is to measure the spectra of nearby stars so that the light of stars passing through the local bubble is absorbed by existing gas and the resulting spectral lines from absorption can be measured. In this study, we use binary stars to trace the local bubble structures through lines such as the Na I Doublet. First, we determined the observed spectral lines of stars by HARPS and FEROS echelle spectrographs. Then, we made synthetic spectra with the ATLAS9 code. Finally, the difference between the observational and synthetic spectra confirms the existence of the Na I Doublet in the local ISM.

• Publications of The Korean Astronomical Society
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• v.27 no.4
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• pp.299-300
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• 2012

We investigate the relation between star formation activity and PAH $3.3{\mu}m$ emission. Our targets are mid-infrared-excess galaxies selected from the AKARI all-sky survey point source catalog. We performed AKARI near-infrared spectroscopy for them. As a result, we obtained $2.5-5{\mu}m$spectra of 79 galaxies, and selected 35 star-forming galaxies out of them. Comparing the PAH $3.3{\mu}m$ luminosities with the infrared luminosities, we find a linear correlation between them. However, by adding the results from literatures for luminous infrared galaxies and ultra-luminous infrared galaxies that are more luminous than our sample, the ratio of the PAH to the infrared luminosity is found to decrease towards the luminous end.