• The Bulletin of The Korean Astronomical Society
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• v.42 no.2
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• pp.58.1-58.1
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• 2017

The NISS (Near-infrared Imaging Spectrometer for Star formation history) is the near-infrared spectro-photometric instrument optimized to the first Next Generation of small satellite (NEXTSat-1). The off-axis optics was developed to cover a wide field of view with 2 deg. ${\times}$ 2 deg. as well as a wide wavelength range from 0.95 to $2.5{\mu}m$. Considering the simple alignment scheme, afocal system was adapted in the optical components. The mechanical structures were tested under the space environment. We have obtained the accurate calibration data using our test facilities under the operational condition. After the final integration of flight model into the satellite, the communication with the satellite and the functional test were passed. The NISS will be launched in early 2018. During around 2-year operation, the spectro-photometric survey covering more than 100 square degree will be performed. To achieve the major scientific objectives for the study of the cosmic star formation in local and distant universe, the main observational targets will be nearby galaxies, galaxy clusters, star-forming regions and low background regions. Here, we report the final performance of the flight model of the NISS.

• Journal of The Korean Astronomical Society
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• v.53 no.5
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• pp.103-115
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• 2020

We analyze the spatially resolved kinematics of gas and stars for a sample of ten hidden type 1 AGNs in order to investigate the nature of their central sources and the scaling relation with host galaxy stellar velocity dispersion. We select our sample from a large number of hidden type 1 AGNs, which are identified based on the presence of a broad (full width at half maximum ≳1000 km s^-1) component in the Hα line profile and which are frequently mis-classified as type 2 AGNs because AGN continuum and broad emission lines are weak or obscured in the optical spectral range. We used the Blue Channel Spectrograph at the 6.5-m Multiple Mirror Telescope to obtain long-slit data with a spatial scale of 0.3 arcsec pixel^-1. We detected broad Hβ lines for only two targets; however, the presence of strong broad Hα lines indicates that the AGNs we selected are all low-luminosity type 1 AGNs. We measured the velocity, velocity dispersion, and flux of stellar continuum and gas emission lines (i.e., Hβ and [O III]) as a function of distance from the center. The spatially resolved gas kinematics traced by Hβ or [O III] are generally similar to the stellar kinematics except for the inner center, where signatures of gas outflows are detected. We compare the luminosity-weighted effective stellar velocity dispersions with the black hole masses and find that our hidden type 1 AGNs, which have relatively low back hole masses, follow the same scaling relation as reverberation-mapped type 1 AGN and more massive inactive galaxies.

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.119-120
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• 2015

We report results of the measurement of the trigonometric parallax of an $H_2O$ maser source in IRAS 22555+6213 with the VLBI Exploration of Radio Astrometry (VERA). The annual parallax was determined to be $0.278{\pm}0.019$ mas, corresponding to a distance of $3.66^{+0.30}_{-0.26}kpc$. Our results confirm that IRAS 22555+6213 is located in the Perseus arm. We computed the peculiar motion of IRAS 22555+6213 to be ($U_{src}$, $V_{src}$, $W_{src}$) = ($0{\pm}1$, $-32{\pm}1$, $9{\pm}1$) $km\;s^{-1}$, where $U_{src}$, $V_{src}$, and $W_{src}$ are directed toward the Galactic center, in the direction of Galactic rotation and toward the Galactic north pole, respectively. IRAS 22555+6213, NGC7538 and Cepheus A lie along the same line of sight, and are within $2^{\circ}$ on the sky. Their parallax distances, with which we derived their absolute position in the Milky Way, show that IRAS 22555+6213 and NGC7538 are associated with the Perseus arm, while Cepheus A is located in the Local arm. We compared the kinematic distances of IRAS 22555+6213 derived with flat and non-flat rotation curve with its parallax distance and found the kinematic distance derived from the non-flat rotation assumption ($-32km\;s^{-1}$ lag) to be consistent with the parallax distance.

• Journal of The Korean Astronomical Society
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• v.43 no.1
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• pp.9-23
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• 2010

In this paper we examined the association of Infrared Dark Cloud (IRDC) cores with YSOs and the geometric properties of the IRDC cores. For this study a total of 13,650 IRDC cores were collected mainly from the catalogs of the IRDC cores published from other studies and partially from our catalog of IRDC cores containing new 789 IRDC core candidates. The YSO candidates were searched for using the GLIMPSE, MSX, and IRAS point sources by the shape of their SED or using activity of water or methanol maser. The association of the IRDC cores with these YSOs was checked by their line-of-sight coincidence within the dimension of the IRDC core. This work found that a total of 4,110 IRDC cores have YSO candidates while 9,540 IRDC cores have no indication of the existence of YSOs. Considering the 12,200 IRDC cores within the GLIMPSE survey region for which the YSO candidates were determined with better sensitivity, we found that 4,098 IRDC cores (34%) have at least one YSO candidate and 1,072 cores among them seem to have embedded YSOs, while the rest 8,102 (66%) have no YSO candidate. Therefore, the ratio of [N(IRDC core with protostars)]/[N(IRDC core without YSO)] for 12,200 IRDC cores is about 0.13. Taking into account this ratio and typical lifetime of high-mass embedded YSOs, we suggest that the IRDC cores would spend about $10^4\sim10^5$ years to form high-mass stars. However, we should note that the GLIMPSE point sources have a minimum detectable luminosity of about $1.2 L_{\odot}$ at a typical IRDC core's distance of ~4 kpc. Therefore, the ratio given here should be a 100ver limit and the estimated lifetime of starless IRDC cores can be an upper limit. The physical parameters of the IRDC cores somewhat vary depending on how many YSO candidates the IRDC cores contain. The IRDC cores with more YSOs tend to be larger, more elongated, and have better darkness contrast than the IRDC cores with fewer or no YSOs.

• Journal of The Korean Astronomical Society
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• v.36 no.4
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• pp.271-282
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• 2003

We present results of a $H^{13}CN$ J=1-0 mapping survey of molecular clouds toward the Galactic Center (GC) region of $-1.6^{\circ}{\le}{\iota}{\le}2^{\circ}$ and $-0.23^{\circ}{\le}b{\le}0.30^{\circ}$ with 2' grid resolution. The $H^{13}CN$ emissions show similar distribution and velocity structures to those of the $H^{12}CN$ emissions, but are found to better trace the feature saturated with $H^{12}CN$ (1-0). The bright components among multi-components of $H^{12}CN$ line profiles usually appear in the $H^{13}CN$ line while most of the dynamically forbidden, weak $H^{12}CN$ components are seldom detected in the $H^{13}CN$ line. We also present results of other complementary observations in $^{12}CO$ (J=1-0) and $^{13}CO$ (J=1-0) lines to estimate physical quantities of the GC clouds, such as fractional abundance of HCN isotopes and mass of the GC cloud complexes. We confirm that the GC has very rich chemistry. The overall fractional abundance of $H^{12}CN$ and $H^{13}CN$ relative to $H_2$ in the GC region is found to be significantly higher than those of any other regions, such as star forming region and dark cloud. Especially cloud complexes nearer to the GC tend to have various higher abundance of HCN. Total mass of the HCN molecular clouds within $[{\iota}]{\le}6^{\circ}$ is estimated to be ${\~}2 {\times}10^7\;M_{\bigodot}$ using the abundances of HCN isotopes, which is fairly consistent with previous other estimates. Masses of four main complexes in the GC range from a few $10^5$ to ${\~}10^7\;M_{\bigodot}$ All the HCN spectra with multi-components for the four main cloud complexes were investigated to compare the line widths of the complexes. The largest mode (45 km $s^{-1}$) of the FWHM distributions among the complexes is in the Clump 2. The value of the mode tends to be smaller at the farther complexes from the GC.

• Journal of The Korean Astronomical Society
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• v.48 no.4
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• pp.213-228
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• 2015

The Horizon Run 4 is a cosmological N-body simulation designed for the study of coupled evolution between galaxies and large-scale structures of the Universe, and for the test of galaxy formation models. Using 6300³ gravitating particles in a cubic box of L_box = 3150 h⁻¹Mpc, we build a dense forest of halo merger trees to trace the halo merger history with a halo mass resolution scale down to M_s = 2.7 × 10¹¹h⁻¹M_⊙. We build a set of particle and halo data, which can serve as testbeds for comparison of cosmological models and gravitational theories with observations. We find that the FoF halo mass function shows a substantial deviation from the universal form with tangible redshift evolution of amplitude and shape. At higher redshifts, the amplitude of the mass function is lower, and the functional form is shifted toward larger values of ln(1/σ). We also find that the baryonic acoustic oscillation feature in the two-point correlation function of mock galaxies becomes broader with a peak position moving to smaller scales and the peak amplitude decreasing for increasing directional cosine μ compared to the linear predictions. From the halo merger trees built from halo data at 75 redshifts, we measure the half-mass epoch of halos and find that less massive halos tend to reach half of their current mass at higher redshifts. Simulation outputs including snapshot data, past lightcone space data, and halo merger data are available at http://sdss.kias.re.kr/astro/Horizon-Run4.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.2
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• pp.68.2-68.2
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• 2013

Camera for QUasars in EArly uNiverse (CQUEAN) is an optical CCD camera system made by Center for Exploration of the Origin of the Universe (CEOU). CQUEAN is developed for follow-up observation of red sources such as high-redshift quasar candidates ($z{\geq}5$), gamma-ray bursts (GRB), brown dwarfs and young stellar objects. The CQUEAN is composed of a science camera with deep-depletion CCD chip which is sensitive at around $1{\mu}m$, a set of custom-made wide-band filters for detection of quasar candidates at z~5, and a guide camera. A focal reducer was developed to secure $4.8^{\prime}{\times}4.8^{\prime}$ field of view, and an in-house user software for efficient data acquisition. CQUEAN was attached to 2.1m Otto Struve Telescope in McDonald Observatory, USA, in August 2010. About 1000 quasar candidates including 3 confirmed with follow-up spectroscopy, have been observed so far, and many high-z galaxy cluster candidates, GRBs and supernovae were also observed. And monitoring of HBC 722, a young stellar object, is under way since 2011. Further enhancement of CQUEAN including the introduction of narrow-band filters is planned.

• Publications of The Korean Astronomical Society
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• v.32 no.1
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• pp.317-319
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• 2017

We propose a cosmological survey to probe star formation and nuclear activity in galaxies at redshifts of z=2-4 by polycyclic aromatic hydrocarbon (PAH) features using the SPICA mid-infrared instrument (SMI) with a spectral resolution of R=20. We will cover a wavelength range of $20-36{\mu}$ that corresponds to z=2-4 for the PAH features (11.3, 7.7, and $6.2{\mu}$). The sensitivity will be $1{\times}10^{-19}W/m^2(5{\sigma})$ in case of a reference survey that covers 4 arcmin2 field in a one-hour observation. It corresponds to $L_{IR}=2{\times}10^{11}L_{\odot}$ at z=3 and will give us more than 10000 galaxies in a 450 hour survey.

• Publications of The Korean Astronomical Society
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• v.32 no.1
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• pp.185-187
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• 2017

Combining the AKARI Point Source Catalog and the 37-month Monitor of All-sky X-ray Image (MAXI) catalog, the infrared and X-ray properties of nearby active galactic nuclei were investigated. The 37-month MAXI catalog tabulates 100 nearby Seyfert galaxies, 73 of which are categorized into Seyfert I galaxies. Among these Seyfert galaxies, 69 ones were found to have an AKARI infrared counterpart. For the Seyfert I galaxies in this sample, a well-known correlation was found between the infrared and X-ray luminosities. However, the observed X-ray luminosity of the Seyfert II galaxies tends to be lower for the infrared luminosity than the Seyfert I galaxies. This suggests that the X-ray absorption is significant in the Seyfert II galaxies. The Seyfert II galaxies seem to have a bimodal distribution of the IR color between $18{\mu}m$ and $90{\mu}m$. Especially, a large fraction of the Seyfert II galaxies exhibits a redder IR color than the Seyfert I galaxies. A possible origin of the redder IR color is briefly discussed, in relation to the star formation activity in the host galaxy, and to the X-ray absorption.

• 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.