• Journal of Astronomy and Space Sciences
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• v.22 no.2
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• pp.89-112
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• 2005

We determine the rotation velocities of 108 spiral and irregular galaxies (XV-Sample) from first-order rotation curves from position-velocity maps, based on short 21-cm observations with the Westerbork Synthesis Radio Telescope (WSRT). To test the usual random motion corrections, we compare the global HI linewidths and the rotation velocities, obtained from kinematical fits to two-dimensional velocity fields for a sample of 28 galaxies (RC-Sample), and find that the most frequently used correction formulae (Tully & Fouque 1985) are not very satisfactory. The rotation velocity parameter (the random-motion corrected HI linewidth: W?), derived with these corrections, may be statistically equal to two times the true rotation velocity, but in individual cases the differences can be large. We analyse, for both RC- and XV-Samples, the dependence of the slope of, and scatter in the Tully-Fisher relation on the definition of the rotation velocity parameters- For the RC-Sample, we find that the scatter in the Tully-Fisher relation can be reduced considerably when the rotation velocities derived from rotation curves are used instead of the random-motion corrected global H I linewidths. No such reduction in the scatter is seen for XV-Sample. We conclude that the reduction of the scatter in the Tully-Fisher relation seems to be related to the use of two-dimensional velocity information: accurate rotation velocity and kinematical inclination.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.71.1-71.1
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• 2019

We report the first high-resolution (sub-arcminute) large-scale mapping $^{12}CO$ and $^{13}CO$ observations of the molecular clouds associated with the giant outer Galaxy H II region CTB 102 (KR 1). These observations were made using a newly commissioned receiver on the 13.7-m radio telescope at the Taeduk Radio astronomy Observatory (TRAO). Our observations show that the molecular clouds have a spatial extent of $60{\times}35pc$ and a total mass of $10^{4.8}-10^{5.0}$ solar mass, Infrared data from WISE and 2MASS were used to identify and classify the YSO population associated with ongoing star formation activity within the molecular clouds. Moving away from the H II region, there is an age/class gradient consistent with sequential star formation. The infrared and molecular line data were combined to estimate the star formation efficiency (SFE) of the entire cloud as well as the SFE for various sub regions of the cloud.

• Journal of The Korean Astronomical Society
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• v.38 no.2
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• pp.97-100
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• 2005

The first Space-VLBI project, VSOP, started successfully with the launch of the dedicated space-VLBI satellite HALCA in 1997. The project has been in scientific operation in the 1.6 GHz and 5 GHz bands, and studies have been done mainly of the jet phenomena related to active galactic nuclei. A second generation space- VLBI project, VSOP-2, has been planned by the working group formed at ISAS/JAXA with many collaborators. The spacecraft is planned to observe in the 8, 22 and 43 GHz bands with cooled receivers for the two higher bands, and with a maximum angular resolution at 43 GHz (7 mm) of about 40 micro-arcseconds. The VSOP-2 satellite will also have the capability of the phase-reference and full polarization observations, which will produce more powerful results than those of the VSOP project. Far-future space-VLBI projects following VSOP and VSOP-2, have a large potential to achieve enough resolution and sensitivity to satisfy astronomers in future.

• Journal of The Korean Astronomical Society
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• v.29 no.spc1
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• pp.193-194
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• 1996

A large scale $^{13}CO$(J=1-0) survey was made for CMa OB1/R1 region in $220^{\circ}{\le}{\iota}{\le}230^{\circ}$ and $-10^{\circ}{\le}b{\le}10^{\circ}$ with a 8' spacing by using the 4 m radio telescope of Nagoya University. 34 isolated clouds were identified in this survey. Among them, two clouds were firstly identified by us. The observed LSR velocity indicate that almost of the all clouds are located in the Local arm, except two extreme velocity. The mass spectrum of the clouds in the Local arm is best fitted by a power-law index of 1.6.

• Journal of The Korean Astronomical Society
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• v.37 no.4
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• pp.223-224
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• 2004

The Tycho supernova remnant (SNR), as one of the few historical SNRs, has been widely studied in various wavebands and previous observations have shown evidence that Tycho is interacting with a dense ambient medium toward the northeast direction, In this paper, we report our high-resolution (16') $^{12}CO$ observation of the remnant using the Nobeyama 45m radio telescope. The Nobeyama data shows that a large molecular cloud surrounds the SNR along the northeastern boundary. We suggest that the Tycho SNR and the molecular cloud are both located in the Perseus arm and that the dense medium interacting with the SNR is possibly the molecular cloud. We also discuss the possible connection between the molecular cloud and the Balmer-dominated optical filaments, and suggest that the preshock gas may be accelerated within the cosmic ray and/or fast neutral precursor.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.1
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• pp.33.2-33.2
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• 2013

We present 12CO ($J=1{\rightarrow}0$) observations of a set of local galaxies (0.04 < z < 0.08) with a large cool gas reservoir, dubbed "HI Monsters". The data were obtained using the Redshift Search Receiver (RSR) on the Five College Radio Astronomy Observatory (FCRAO) 14 m telescope. The sample consists of 20 galaxies with $M_{HI}$ > $3{\times}10^{10}M_{\odot}$ identified by the ALFALFA survey and 8 additional objects with comparable HI mass from a separate LSB galaxy study ($M_{HI}$ > $1.5{\times}10^{10}M_{\odot}$). Our sample selection is purely based on the amount of neutral hydrogen in galaxies, thereby providing a chance to study how atomic and molecular gas relate to each other in these extremely HI-rich systems. We have detected CO in 15 out of 20 ALFALFA selected HI Monsters and 4 out of 8 LSB HI Monsters. We present the global molecular gas properties of the sample and discuss how their molecular gas properties correlate with their star formation activities.

• Journal of the Institute of Convergence Signal Processing
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• v.18 no.1
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• pp.13-20
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• 2017

In this paper, we evaluate the basic test results of the 32 Gbps observational equipment introduced as the back-end system for the wideband VLBI (Very Long Baseline Interferometry) observation of KVN (Korean VLBI Network). Radio astronomers want to make a large radio telescope that has excellent performance in order to observe the superfine structure of a celestial body, but a lot of money is needed. Therefore, in order to increase the sensitivity, the performance improvement of the receiving system and the method of observing the wide frequency bandwidth are introduced. To do this, we adopted a wideband sampling method for converting analog signals to digital with ultra-fast speeds and a wideband sampler for performing digital filtering in order to observe a wide observational frequency bandwidth. The wideband sampler (OCTAD-K) supports up to 16 Gsps-2bits sampling and supports a variety of observational bandwidth using digital filtering techniques. In particular, it is designed to support KVN's 4-frequency simultaneous observation system and VERA(VLBI Exploration of Radio Astrometry)'s 2-beam observation system. It can also support polKVN(Korean VLBI Network), KaVA(KVN and VERA Array), 32Gbps Direct Sampler, Digital Filter, Widebandarization observations and supports the standard VDIF(VLBI Data Interchange Format) format of observed data. In this paper, the performance of the system and the problem solving are described in detail after performing the factory inspection and field test before the system is introduced.

• Journal of Astronomy and Space Sciences
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• v.39 no.2
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• pp.43-50
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• 2022

The unified scheme of Seyfert galaxies hypothesizes that the observed differences between the two categories of Seyfert galaxies, type 1 (Sy1) and type 2 (Sy2) are merely due to the difference in the orientation of the toroidal shape of the obscuring material in the active galactic nuclei. We used in this paper, a sample consisting of 120 Seyfert galaxies at 1.40 × 10⁹ Hz in radio, 2.52 × 10¹⁷ Hz in X-ray and 2.52 × 10²³ Hz in γ-ray luminosities observed by the Fermi Large Area Telescope (Fermi-LAT) in order to test the unified scheme of radio-quiet Seyfert galaxies. Our main results are as follows: (i) We found that the distributions of multiwave luminosities (L_radio, L_X-ray, and L_γ-ray) of Sy1 and Sy2 are completely overlapped with up to a factor of 4. The principal component analysis result reveals that Sy1 and Sy2 also occupy the same parameter spaces, which agrees with the notion that Sy1 and Sy2 are the same class objects. A Kolmogorov-Smirnov test performed on the sub-samples indicates that the null hypothesis (both are from the same population) cannot be rejected with chance probability p ~ 0 and separation distance K = 0.013. This result supports the fact that there is no statistical difference between the properties of Sy1 and Sy2 (ii) We found that the coefficient of the best-fit linear regression equation between the common properties of Sy1 and Sy2 is significant (r > 0.50) which plausibly implies that Sy1 and Sy2 are the same type of objects observed at different viewing angle.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.80.1-80.1
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• 2014

We made simultaneous surveys of 22 GHz water and 44 / 95 GHz methanol masers toward 299 high-mass protostellar objects using the Korea VLBI Network (KVN) 21-m telescope. The sources were selected from the catalog of Red MSX Source (RMS) survey. Initial selection of the sample present high-mass protostellar objects in an evolutionary phase prior to ultra-compact HII regions, which have bolometric luminosities > $10^3L_{\odot}$ but are not associated with any radio continuum emission. After the follow-up work of ongoing RMS survey, final samples contains 56 sources classified as HII regions. We performed a simultaneous survey of 22 GHz water and 44 GHz methanol masers in 2011 and then conducted a simultaneous survey of 22 GHz water and 44 / 95 GHz methanol masers in 2012. The primary scientific goals of these surveys are to investigate the relationship among the three masers and to explore the relationship between each maser and the central star or the parental dense core. The detection rates of two epochs are 42% and 38% for water, 25% and 26% for 44 GHz methanol, and 23% (2012 only) for 95 GHz methanol masers. We performed a statistical analysis on subsample associated with a large data found in literature. In this poster, we will the preliminary data analysis results and discuss the implications.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.2
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• pp.62.2-62.2
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• 2016

We present a newly developed algorithm based on a Bayesian method for 2D tilted-ring analysis of disk galaxies which operates on velocity fields. Compared to the conventional ones based on a chi-squared minimisation procedure, this new Bayesian-based algorithm less suffers from local minima of the model parameters even with high multi-modality of their posterior distributions. Moreover, the Bayesian analysis implemented via Markov Chain Monte Carlo (MCMC) sampling only requires broad ranges of posterior distributions of the parameters, which makes the fitting procedure fully automated. This feature is essential for performing kinematic analysis of an unprecedented number of resolved galaxies from the upcoming Square Kilometre Array (SKA) pathfinders' galaxy surveys. A standalone code, the so-called '2D Bayesian Automated Tilted-ring fitter' (2DBAT) that implements the Bayesian fits of 2D tilted-ring models is developed for deriving rotation curves of galaxies that are at least marginally resolved (> 3 beams across the semi-major axis) and moderately inclined (20 < i < 70 degree). The main layout of 2DBAT and its performance test are discussed using sample galaxies from Australia Telescope Compact Array (ATCA) observations as well as artificial data cubes built based on representative rotation curves of intermediate-mass and massive spiral galaxies.