• Publications of The Korean Astronomical Society
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• v.15 no.spc1
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• pp.1-13
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• 2000

We review the early historical developement of astronomical spectrographs, properties of emission line spectra of HII regions in spiral galaxies, and absorption line features of galactic globular clusters. Emission line spectra of HII regions within three spiral galaxies NGC 300, NGC 1365, and NGC 7793, which were observed from AAT/IPCS, had been analysed, and we discuss the abundances of elements in HII regions and the radial abundace gradients through the galaxies. The radial UBV color variations of two globular clusters, NGC 1851 and NGC 2808, were examined for correlations with radial variations of several absorption lines in the integrated spectra, which were obtained from SAAO 74 inch telescope and image tube spectrograph. Nine giant star's spectra in NGC 3201 were also obtained and analysed for the radial abundance gradients in the globular cluster. The results show that the presence of a radial color gradient in a globular cluster is correlated with the presence of abundance gradients. Finally, we suggest some scientific programs for the new high dispersion spectrograph, which will be installed to the BOAO 1.8m telescope.

• Publications of The Korean Astronomical Society
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• v.27 no.4
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• pp.335-338
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• 2012

We present the $18{\mu}m$ luminosity function (LF) of galaxies at 0.006 < z < 0.8 (the average redshift is ~ 0.04) using the AKARI mid-infrared All-Sky Survey catalogue. We have selected 243 galaxies at $18{\mu}m$ from the Sloan Digital Sky Survey (SDSS) spectroscopic region. These galaxies then have been classified into five types; Seyfert 1 galaxies (Sy1, including quasars), Seyfert 2 galaxies (Sy2), low ionization narrow emission line galaxies (LINER), galaxies that are likely to contain both star formation and Active Galactic Nuclei (AGN) activities (composites), and star forming galaxies (SF) using optical emission lines such as the line width of $H{\alpha}$ or the emission line ratios of [OIII]/$H{\beta}$ and [NII]/$H{\alpha}$. As a result of constructing the LF of Sy1 and Sy2, we found the following results; (i) the number density ratio of Sy2 to Sy1 is $1.64{\pm}0.37$, larger than the results obtained from optical LF and (ii) the fraction of Sy2 in the entire AGN population may decrease with $18{\mu}m$ luminosity. These results suggest that most of the AGNs in the local universe are obscured by dust and the torus structure probably depends on the mid-infrared luminosity.

• Journal of The Korean Astronomical Society
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• v.36 no.3
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• pp.145-148
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• 2003

P-Cygni type Ly$\alpha$ from starburst galaxies, either nearby galaxies or Lyman Break galaxies, are believed to be formed by galactic outflows such as galactic supershells or galactic superwinds. We develope a Monte Carlo code to calculate the Ly$\alpha$ line transfer in a galactic supershell which is expanding and formed of uniform and dusty neutral hydrogen gas. The escape of Ly$\alpha$ photons from the system is achieved by a number of back-scatterings. A series of emission peaks are formed by back-scatterings. When we observe P-Cygni type Ly$\alpha$ emissions of starforming galaxies, we can usually see merely singly-peaked emission. Hence the secondary and the tertiary emission humps should be destroyed. In order to do this, dust should be spatially more extended into the inner cavity than neutral supershell. We find that the kinematic information of the expanding supershell is conserved even in dusty media. We discuss the astrophysical applications of our results.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.1
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• pp.33.1-33.1
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• 2012

We investigate the disk-jet connection of Young Radio Galaxies (YRGs) by comparing emission-line properties with radio luminosity and jet size. By combining new optical spectra for 21 objects with SDSS archival data for 15 objects, we selected a sample of 36 low-redshift YRGs at z < 0.4. We find that YRGs are classified in high- and low-excitation galaxies based on the relative strength of high-to-low excitation line strengths, suggesting that there are two populations in YRGs as similarly found in large radio galaxies, i.e., FRIs and FRIIs. High-excitation galaxies (HEGs) have higher emission line luminosities than low-excitation galaxies (LEGs) at fixed black hole mass and radio luminosity, suggesting that the Eddington ratio is higher in HEGs than in LEGs and that for given radio activity HEGs have higher accretion activity than LEGs. The difference between HEGs and LEGs is probably due to either mass accretion rate or radiative efficiency.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.1
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• pp.58.1-58.1
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• 2013

We present $10{\mu}m-35{\mu}m$ Spitzer spectra of the interstellar medium in the Central Molecular Zone (CMZ), the central 210 pc ${\times}$ 60 pc of the Galactic center (GC). We present maps of the CMZ in ionic and $H_2$ emission, covering a more extensive area than earlier spectroscopic surveys in this region. The radial velocities and intensities of ionic lines and $H_2$ suggest that most of the $H_2$ 0-0 S(0) emission comes from gas along the line-of-sight, as found by previous work. We compare diagnostic line ratios measured in the Spitzer Infrared Nearby Galaxies Survey (SINGS) to our data. Previous work shows that forbidden line ratios can distinguish star-forming galaxies from LINERs and AGNs. Our GC line ratios agree with star-forming galaxies and not with LINERs or AGNs.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.85.1-85.1
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• 2012

Energetic outflow from active galactic nuclei (AGNs) may play a critical role in galaxy evolution. We present a velocity diagnostics for detecting gas outflow in the narrow-line region of Type-2 AGNs using line-of-sight velocity offset of the [O III]${\lambda}5007$ and $H{\alpha}$ emission lines with respect to the systemic velocity of stars in host galaxies. We apply the diagnostics to nearby galaxies at 0.02 < z < 0.05: 3775 AGN-host and 907 star-forming galaxies as a comparison sample, which are selected from the Sloan Digital Sky Survey DR7. After obtaining a best-fit stellar population model for the continuum and a systemic velocity based on stellar lines, we subtract stellar component to measure velocity offsets of each emission line. We find a sample of 169 AGN-host galaxies with outflow signatures, displaying a larger velocity shift of [O III] than that of $H{\alpha}$, as expected in a decelerating outflow model. We find that the offset velocity of [O III] increases with Eddington ratio, suggesting that gas outflow depends on the energetics of AGN.

• Journal of The Korean Astronomical Society
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• v.44 no.2
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• pp.59-65
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• 2011

A small number of active galactic nuclei are known to exhibit prominent double peak emission profiles that are well-fitted by a relativistic accretion disk model. We develop a Monte Carlo code to compute the linear polarization of a double peaked broad emission line arising from Thomson scattering. A Keplerian accretion disk is adopted for the double peak emission line region and the geometry is assumed to be Schwarzschild. Far from the accretion disk where flat Minkowski geometry is appropriate, we place an azimuthally symmetric scattering region in the shape of a spherical shell sliced with ${\Delta}{\mu}=0.1$. Adopting a Monte Carlo method we generate line photons in the accretion disk in arbitrary directions in the local rest frame and follow the geodesic paths of the photons until they hit the scattering region. The profile of the polarized flux is mainly determined by the relative location of the scattering region with respect to the emission source. When the scattering region is in the polar direction, the degree of linear polarization also shows a double peak structure. Under favorable conditions we show that up to 0.6% linear polarization may be obtained. We conclude that spectropolarimetry can be a powerful probe to reveal much information regarding the accretion disk geometry of these active galactic nuclei.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.73.2-73.2
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• 2011

We present a new database of absorption and emission-line measurements based on the entire spectral atlas from the Sloan Digital Sky Survey (SDSS) 7th data release of galaxies within a redshift of 0.2. Our work makes use of the publicly available penalized pixel-fitting(pPXF) and gas and absorption line fitting (gandalf) IDL codes, aiming to improve the existing measurements for stellar kinematics, the strength of various absorption-line features, and the flux and width of the emissions from different species of ionized gas. Our fit to the stellar continuum uses both standard stellar population models and empirical templates obtained by combining a large number of stellar spectra in order to fit a subsample of high-quality SDSS spectra for quiescent galaxies. Furthermore, our fit to the nebular spectrum includes an exhaustive list of both recombination and forbidden lines. Foreground Galactic extinction is implicitly treated in our models, whereas reddening in the SDSS galaxies is included in the form of a simple dust screen component affecting the entire spectrum that is accompanied by a second reddening component affecting only the ionised gas emission. Most notable of our work is that, we provide quality of the fit to assess reliability of the measurements. The quality assessment can be highly effective for finding new classes of objects. For example, based on the quality assessment around the Ha and [NII] nebular lines, we found approximately 1% of the SDSS spectra which classified as "galaxies" by the SDSS pipeline are in fact type I Seyfert AGN.

• Publications of The Korean Astronomical Society
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• v.27 no.4
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• pp.243-248
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• 2012

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.

• Journal of The Korean Astronomical Society
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• v.35 no.4
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• pp.175-185
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• 2002

Almost half of primeval galaxies show P-Cygni type profiles in the Ly$\alpha$ emission line. The main underlying mechanism for the profile formation in these systems is thought to be the frequency re-distribution of the line photons in expanding scattering media surrounding the emission source. A Monte Carlo code is developed to investigate the Ly$\alpha$ line transfer in an optically thick and moving medium with a careful consideration of the scattering in the damping wings. Typical column densities and expansion velocities of neutral hydrogen investigated in this study are $N_{H1}{\~}10^{17-20}\;cm^{-2}$ and ${\Delta}V{\~} 100 km\;s^{-1}$. We investigate the dependence of the emergent profiles on the kinematics and on the column density. Our numerical results are applied to show that the damped Ly$\alpha$ absorbers may possess an expanding H I supershell with bulk flow of ${\~}200 km\;s^{-l}$ and H I column density $N_{H1}{\~}10^{19}\;cm^{-2}$. We briefly discuss the observational implications.