• Publications of The Korean Astronomical Society
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• v.32 no.1
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• pp.11-15
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• 2017

We present the AKARI far-infrared (FIR) all-sky maps and describe its characteristics, calibration accuracy and scientific capabilities. The AKARI FIR survey has covered 97% of the whole sky in four photometric bands, which cover continuously 50-180 micron with band central wavelengths of 65, 90, 140, and 160 microns. The data have been publicly released in 2014 (Doi et al., 2015) with improved data quality that have been achieved since the last internal data release (Doi et al., 2012). The accuracy of the absolute intensity is ${\leq}10%$ for the brighter regions. Quantitative analysis of the relative intensity accuracy and its dependence upon spatial scan numbers has been carried out. The data for the first time reveal the whole sky distribution of interstellar matter with arcminute-scale spatial resolutions at the peak of dust continuum emission, enabling us to investigate large-scale distribution of interstellar medium in great detail. The filamentary structure covering the whole sky is well traced by the all-sky maps. We describe advantages of the AKARI FIR all-sky maps for the study of interstellar matter comparing to other observational data.

• Journal of The Korean Astronomical Society
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• v.38 no.2
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• pp.169-172
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• 2005

We present CO(3-2), CO(2-1), and 230 GHz (1.3 mm) continuum images of nearby galaxies taken with the Submillimeter Array (SMA). Our main topic is to study the relation between higher-J molecular gas (e.g., CO J=3-2, 2-1) and nuclear activities (e.g., active galactic nuclei [AGNs] and starbursts). The nearby Seyfert 2 galaxy M51 shows strong CO(3-2) emission from the circumnuclear molecular gas, with an intensity twice as strong as that of the CO(1-0) emission. Strong CO(3-2) emission enhancement suggests that the circum nuclear molecular gas in M51 is warm and dense, which may be related to the AGN activities. Molecular gas in the nearby moderate starburst galaxy NGC 6946 is distributed along the large-scale bar or spiral arms and along the minibar, and the multi-J CO line images show very similar distribution to each other. For this galaxy, there is no clear enhancement in higher-J lines as seen in M51, which may be because NGC 6946 does not have clear AGN activities. Based on the results of these two galaxies, the physical conditions of the circum nuclear molecular gas may be related to the AGN activities. We also observed the nearby edge-on starburst galaxy NGC 3628 and the starburst/Seyfert composite galaxy NGC 4945 with the CO(2-1) line and 230 GHz (1.3 mm) continuum emission. These information will give us some hints for understanding the relation between nuclear activities and circum nuclear molecular gas and dust.

• Journal of The Korean Astronomical Society
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• v.48 no.6
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• pp.357-364
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• 2015

We observe ten known 22GHz H₂O maser galaxies during February 19-22, 2011 using the 21 m Tamna telescope of the Korean VLBI Network and a new wide-band digital spectrometer. Simultaneously we searched for 43GHz SiO v = 1, 2, J = 1-0 maser emission. We detect H₂O maser emission towards five sources (M 33, NGC 1052, NGC 1068, NGC 4258, M 82), with non-detections towards the remaining sources (UGC 3193, UGC 3789, Antennae H₂O-West, M 51, NGC 6323) likely due to sensitivity. Our 22GHz spectra are consistent with earlier findings. Our simultaneous 43GHz SiO maser search produced non-detections, yielding - for the first time - upper limits on the 43GHz SiO maser emission in these sources at a 3 σ sensitivity level of 0.018K-0.033K (0.24 Jy-0.44 Jy) in a 1.75 km s⁻¹ velocity resolution. Our findings suggest that any 43GHz SiO masers in these sources (some having starburst-associated H₂O kilomasers) must be faint compared to the 22GHz H₂O maser emission.

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.517-519
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• 2015

A large-scale neutral hydrogen ($H\small{I}$) ring serendipitously found in the Leo I galaxy group is 200 kpc in diameter with $M_{H\small{I}}{\sim}1.67{\times}10^9M_{\odot}$, unique in size in the Local Universe. It is still under debate where this $H\small{I}$ ring originated - whether it has formed out of the gas remaining after the formation of a galaxy group (primordial origin) or been stripped during galaxy-galaxy interactions (tidal origin). We are investigating the optical and $H\small{I}$ gas properties of the dwarf galaxies located within the gas ring in order to probe its formation mechanism. In this work, we present the photometric properties of the dwarfs inside the ring using the CFHT MegaCam $u^{\ast}$, $g^{\prime}$, $r^{\prime}$ and $i^{\prime}$-band data. We discuss the origin of the gas ring based on the stellar age and metal abundance of dwarf galaxies contained within it.

• Journal of The Korean Astronomical Society
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• v.40 no.4
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• pp.187-188
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• 2007

This contribution to the IV Korea-Mexico meeting deals with the hydrodynamics of the matter reinserted within super star clusters (SSCs) by both stellar winds and supernova explosions, results recently printed in The Astrophysical Journal (Silich et al. 2007). The motivation of such a project arose from the persistent presence of the small mass and compact HII regions that sit right on top of many massive and compact SSCs, from which one expects a large mechanical energy power. The data used for our calculations appear only recently (see Smith et al. 2006) for the massive and compact SSC M82-A1. We presented in our paper the calculated flow, derived through analytical and semi-analytical methods, which led to almost identical results. We have found out that the only way of accommodating a compact HII region (4.5 pc in radius, in the case of M82-A1) on top of a 6.3 Myr old and massive (> $10^6M_{\bigodot}$) SSC with a half light radius of 3 pc, requires of two assumptions: a very low heating efficiency (< 10%) within the cluster, what leads to a bimodal solution (see Tenorio-Tagle et al. 2007) and a high pressure in the surrounding medium.

• Publications of The Korean Astronomical Society
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• v.27 no.4
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• pp.253-256
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• 2012

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.

• Publications of The Korean Astronomical Society
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• v.27 no.4
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• pp.353-356
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• 2012

We present new constraints on the cosmic optical background (COB) obtained from an analysis of the Pioneer 10/11 Imaging Photopolarimeter (IPP) data. After careful examination of the data quality, the usable measurements free from the zodiacal light are integrated into sky maps at the blue (${\sim}0.44{\mu}m$) and red (${\sim}0.64{\mu}m$) bands. Accurate starlight subtraction was achieved by referring to all-sky star catalogs and a Galactic stellar population synthesis model down to 32.0 mag. We find that the residual light is separated into two components: one component shows a clear correlation with the thermal $100{\mu}m$ brightness, whilst the other shows a constant level in the lowest $100{\mu}m$ brightness region. The presence of the second component is significant after all the uncertainties and possible residual light in the Galaxy are taken into account, thus it most likely has an extragalactic origin (i.e., the COB). The derived COB brightness is ($(1.8{\pm}0.9){\times}10^{-9}$ and $(1.2{\pm}0.9){\times}10^{-9}\;erg\;s^{-1}\;cm^{-2}\;sr^{-1}\;{\AA}^{-1}$ in the blue and red spectral regions, respectively, or $7.9{\pm}4.0$ and $7.7{\pm}5.8\;nW\;m^{-2}\;sr^{-1}$. Based on a comparison with the integrated brightness of galaxies, we conclude that the bulk of the COB is comprised of normal galaxies which have already been resolved by the current deepest observations. There seems to be little room for contributions from other populations including "first stars" at these wavelengths. On the other hand, the first component of the IPP residual light represents the diffuse Galactic light (DGL)-scattered starlight by the interstellar dust. We derive the mean DGL-to-$100{\mu}m$ brightness ratios of $2.1{\times}10^{-3}$ and $4.6{\times}10^{-3}$ at the two bands, which are roughly consistent with previous observations toward denser dust regions. Extended red emission in the diffuse interstellar medium is also confirmed.

• Journal of The Korean Astronomical Society
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• v.37 no.5
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• pp.563-570
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• 2004

Turbulence is a crucial component of dynamics of astrophysical fluids dynamics, including those of ISM, clusters of galaxies and circumstellar regions. Doppler shifted spectral lines provide a unique source of information on turbulent velocities. We discuss Velocity-Channel Analysis (VCA) and its offspring Velocity Coordinate Spectrum (VCS) that are based on the analytical description of the spectral line statistics. Those techniques are well suited for studies of supersonic turbulence. We stress that a great advantage of VCS is that it does not necessary require good spatial resolution. Addressing the studies of mildly supersonic and subsonic turbulence we discuss the criterion that allows to determine whether Velocity Centroids are dominated by density or velocity. We briefly discuss ways of going beyond power spectra by using of higher order correlations as well as genus analysis. We outline the relation between Spectral Correlation Functions and the statistics available through VCA and VCS.

• Publications of The Korean Astronomical Society
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• v.32 no.1
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• pp.147-149
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• 2017

Since the launch of the Herschel Space Observatory, our understanding about the photo-dissociation regions (PDR) has taken a step forward. In the bandwidth of the Fourier Transform Spectrometer (FTS) of the Spectral and Photometric Imaging REceiver (SPIRE) on board Herschel, ten CO rotational transitions, including J = 4 - 3 to J = 13 - 12, and three fine structure lines, including [$C{\small{I}}$] 609, [$C{\small{I}}$] 370, and [$N{\small{II}}$] $205{\mu}m$, are covered. I present our findings from the FTS observations at the nuclear region of M83, based on the spatially resolved physical parameters derived from the CO spectral line energy distribution (SLED) map and the comparisons with the dust properties and star-formation tracers. This article discusses (1) the potential of using [$N{\small{II}$] 205 and [$C{\small{I}}$] $370{\mu}m$ as star-formation tracers; (2) the excitation mechanisms of warm CO in the nuclear region of M83.

• Journal of The Korean Astronomical Society
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• v.40 no.4
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• pp.161-164
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• 2007

We calculate the evolution of multiple supernova (SN) explosions inside a pre-exiting bubble blown up by winds from massive stars, using one-dimensional hydrodynamic simulations including radiative cooling and thermal conduction effects. First, the development of the wind bubble driven by collective winds from multiple stars during the main sequence is calculated. Then multiple SN explosion is loaded at the center of the bubble and the evolution of the SN remnant is followed for $10^6$ years. We find the size and mass of the SN-driven shell depend on the structure of the pre-existing wind bubble as well as the total SN explosion energy. Most of the explosion energy is lost via radiative cooling, while about 10% remains as kinetic energy and less than 10% as thermal energy of the expanding bubble shell. Thus the photoionization and heating by diffuse radiation emitted by the shock heated gas is the most dominant form of SN feedback into the surrounding interstellar medium.