• The Bulletin of The Korean Astronomical Society
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• v.40 no.2
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• pp.47.2-47.2
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• 2015

We present a large scale structure consisting of eight galaxy filaments around the Virgo cluster in the window of -20 Mpc < SGX, SGZ < 20 Mpc, and 4 Mpc < SGY < 32 Mpc using the HyperLEDA database. While six of the filaments were reported in previous studies, two filaments are newly found in this study. We exploited a large number of faint ($M_B$ < -10) galaxies in comparison with previous studies, which facilitates defining filaments more clearly. The previously known filaments are all in SGY < 16 Mpc and appear to distribute in association with the Virgo cluster in galaxy distribution. Moreover, peculiar velocities of galaxies in these filaments show a distinct offset from the Hubble flow indicating their infall motion toward the Virgo cluster. All of these results confirm that these filamentary structures are under the gravitational influence of the Virgo cluster. Both of the newly discovered filaments are located beyond the 'zero-velocity surface' of the Virgo cluster. One of them is associated in the NGC5353/4 group and the other one appears to penetrates the W and M group of the Virgo cluster. The filamentary structure around the Virgo cluster consisting mainly of the dwarf galaxies allows us to achieve a better understanding of large scale structure and its influence on the build-up of the galaxy cluster at z~0.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.2
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• pp.41.2-41.2
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• 2017

Discovered as the second highest S/N detection of the Planck SZ survey, PLCK G287.0+32.9 is a massive galaxy cluster that belongs to a rare collection of merging clusters that exhibit two radio relics and a radio halo. A feature that makes this cluster even more unique is the separation of the radio relics with one $\sim 400$ kpc to the north-west of the X-ray peak and the other $\sim 2.8$ Mpc to the south-east. This asymmetric configuration requires a complex merging scenario. A key to gaining insight into the events that caused the formation of the merging features is to understand the dark matter mass distribution. Using a weak-lensing technique on deep Subaru and Hubble Space Telescope observations, we map the dark matter mass distribution of PLCK G287.0+32.9. Our investigation detects five significant mass structures. The mass is dominated by a primary structure that is centered near the X-ray peak of the intracluster medium. Four lesser mass structures are detected with two located within $\sim 1\arcmin$ of the primary mass structure, a third to the north-west, and a fourth near the south-east radio relic. Along with these detections, we estimate the mass of each structure and relate their distributions to the intracluster medium and galaxy distributions. In addition, we discuss the relation of the mass structures to the formation of the relics and plausible merging scenarios.

• Journal of Astronomy and Space Sciences
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• v.34 no.3
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• pp.183-197
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• 2017

We present simulations of the optical-band images of high-redshift galaxies utilizing 845 near-ultraviolet (NUV) images of nearby galaxies obtained through the Galaxy Evolution Explorer (GALEX). We compute the concentration (C), asymmetry (A), Gini (G), and $M_{20}$ parameters of the GALEX NUV/Sloan Digital Sky Survey r-band images at z ~ 0 and their artificially redshifted optical images at z = 0.9 and 1.6 in order to quantify the morphology of galaxies at local and high redshifts. The morphological properties of nearby galaxies in the NUV are presented using a combination of morphological parameters, in which early-type galaxies are well separated from late-type galaxies in the $G-M_{20}$, $C-M_{20}$, A-C, and $A-M_{20}$ planes. Based on the distribution of galaxies in the A-C and $G-M_{20}$ planes, we examine the morphological K-correction (i.e., cosmological distance effect and bandshift effect). The cosmological distance effect on the quantitative morphological parameters is found to be significant for early-type galaxies, while late-type galaxies are more greatly affected by the bandshift effect. Knowledge of the morphological K-correction will set the foundation for forthcoming studies on understanding the quantitative assessment of galaxy evolution.

• Journal of the Korea Convergence Society
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• v.8 no.12
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• pp.249-255
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• 2017

Recently, among smart phone functions, cameras are one of the most popular functions and have become one of the most influential functions for purchasing smartphones. However, the basic camera application of the smart phone has a complicated user environment, which is causing many difficulties for the first time user. In this study, Galaxy S7, which is the newest Galaxy S series among the most used Galaxy S series in Korea, was selected and the usability test of the camera application was limited to shooting and editing sharing functions. As a result, first, improvement of icon graphic and label of text form should be provided at the same time to increase the recognition rate and attention of the icon. Second, it is necessary to simplify the structure and provide an intuitive interface in order to facilitate access to various modes and functions. Third, it is necessary to simplify the provision of personalized customized menus or functions in the development of the camera application because it causes a high failure rate and inconvenience in the special functions which are not widely used.

• Publications of The Korean Astronomical Society
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• v.30 no.2
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• pp.409-411
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• 2015

Galaxy clusters, the largest gravitationally bound systems, are an important subject of study to place constraints on cosmological models. Moreover, they are excellent places to test galaxy evolution models in connection to their environments. To date, massive clusters have been found unexpectedly (Kang & Im 2009; Gonzales et al. 2012) and the evolution of galaxies in clusters is still controversial (Elbaz et al. 2007; Faloon et al. 2013). Finding galaxy cluster candidates at z > 1 in a wide, deep imaging survey data will enable us to solve such issues of modern extragalactic astronomy. We report new candidate galaxy clusters in one of the wide and deep survey fields, the European Large Area ISO Survey North1 (ELAIS-N1) and North2 (ELAIS-N2) fields, covering a sky area of $8.75deg^2$ and $4.85deg^2$ each. We also suggest a new useful color selection technique to separate z > 1 galaxies from low - z galaxies by combining multi-wavelength data.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.37.2-37.2
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• 2019

Recent investigations of the double red clump in the color-magnitude diagram of the Milky Way bulge cast serious doubts on the structure and formation origin of the outer bulge. Unlike previous interpretation based on an X-shaped bulge, stellar evolution models and CN-band observations have suggested that this feature is another manifestation of the multiple stellar population phenomenon observed in globular clusters (GCs). This new scenario requires a significant fraction of the outer bulge stars with chemical patterns uniquely observed in GCs. Here we show from homogeneous high-quality spectroscopic data that the red giant branch stars in the outer bulge ($>5.5^{\circ}$ from the Galactic center) are clearly divided into two groups according to Na abundance in the [Na/Fe] - [Fe/H] plane. The Na-rich stars are also enhanced in Al, while the differences in O and Mg are not observed between the two Na groups. The population ratio and the Na and Al differences between the two groups are also comparable with those observed in metal-rich GCs. Since these chemical patterns and characteristics are only explained by stars originated in GCs, this is compelling evidence that the outer bulge was mostly assembled from disrupted proto-GCs in the early history of the Milky Way. We will also discuss the implications of this result on the formation of the early-type galaxies in general.

• The Bulletin of The Korean Astronomical Society
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• v.32 no.2
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• pp.46.2-46.2
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• 2007

• The Bulletin of The Korean Astronomical Society
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• v.44 no.2
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• pp.35.4-35.4
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• 2019

Understanding the interplay between galaxies and dark matter in the universe is one of key challenges in modern astrophysics. This provides an important test of structure formation scenarios and cosmological models. I discuss three aspects of this test: (1) comparing the matter distribution from galaxy redshift surveys with that from weak-lensing surveys, (2) statistical comparison of large-scale structures between observations and cosmological simulations, and (3) multi-wavelength study of galaxies. These tests underscore the importance of combining photometric and spectroscopic surveys in observations along with cosmological simulations for exploring and understanding the structure formation.

• Journal of The Korean Astronomical Society
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• v.30 no.1
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• pp.83-94
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• 1997

We have identified the candidates for the primordial galaxies in the process of formation in the Hubble Deep Field (hereafter HDF). In order to select these objects we have removed objects brighter than 29-th magnitude in the HDF images and smoothed the maps with the Gaussian filters with the FWHM of 0.8' and 4' to obtain the difference maps. This has enabled us to find. very faint diffuse structures close to the sky level. Peaks are identified in the difference map for each of three HDF chips with three filters (F450W, F606W, and F814W). They have the apparent AB magnitudes typically between 29 and 31. The objects identified in different wavelengths filters have a strong cross-correlations. The correlation lengths are about 0.8'. This means that an object found in one filter can be also found as a peak within 0.8' separation in another filter, thus telling the reality of the identified objects. This angular scale is also the size of the primordial galaxies which have strong color fluctuations on their surfaces. Their large-scale distribution quite resembles that of nearby galaxies, supporting the idea that these objects are ancestors of the present bright galaxies forming at statistically high density regions. Inspections on individual objects show that these primordial galaxy candidates have tiny multiple glares embedded in diffuse backgrounds. Their radial light distributions are quite different from that of nearby bright galaxies. We may be now looking at the epoch of galaxy formation.

• Publications of The Korean Astronomical Society
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• v.16 no.1
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• pp.15-20
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• 2001

We observed the thermal transitions of SiO (J=I-0, 2-1) and $^{29}SiO$ (J=l-O) toward the Sgr A molecular clouds. The distribution and the velocity structure of SiO are very similar to previous results for 'quiet' interstellar molecules. We think· that the SiO has been well mixed with other molecules such as $H_2$ which may indicate that the formation of Sgr A molecular clouds was affected by the activities, such as shock waves or energetic photons, from the Galactic center in large scales. The total column density of SiO is about $4.1\times10^{14} cm^{-2}$ and the fractional abundance $SiO/H_2$ appears to be about 10 times larger than those of other clouds in the central region of our galaxy. The derived values are thought to be lower limits since the optical depths of the observed SiO lines are not very thin. The formation of SiO has been known to be critically related to shocks, and our results provide informative data on the environment of our Galactic center.