• 천문학회보
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• 제39권1호
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• pp.41.1-41.1
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• 2014

Although the link between activity in the nuclei of galaxy and galactic mergers has been under scrutiny for several years, it is still unclear to what extent and for which populations of active galaxies merger-triggered activity is relevant. The environment of AGN allows an indirect probe of the past merger history and future merger probability of these systems, suffering less from sensitivity issues while extending to higher redshifts, compared to traditional morphological studies of AGN host galaxies. Here we present results from our investigation of the environment of radio selected sources out to redshift z=2. We employ the first data release J-band catalog from the new near-IR Infrared Medium-Deep Survey (IMS) and 1.4 GHz radio data from the Faint Images of the Radio Sky at Twenty-cm (FIRST) survey and a deep dedicated VLA survey of the VIMOS field, covering a combined total of ~20 sq. degrees. Given the flux limit of the combined radio catalog (0.1 mJy), we probe a radio luminosity range of 10^36-10^44 erg/s. Using the second and fifth closest neighbor density parameters, we test whether active galaxies inhabit denser environments and study these overdensities in terms of both distance to the AGN and its luminosity. We find evidence for a sub-population of radio-selected AGN that resides in significantly overdense environments at small scales, although we do not find significant overdensities for the bulk of our sample. We do not recover any dependence between the AGN radio-luminosity and overdensities. We show that radio-AGN inhabiting the most underdense environments in the field have vigorous ongoing star formation. We interpret these results in terms of the triggering and fuelling mechanism of radio-AGN.

• 천문학논총
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• 제30권2호
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• pp.447-449
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• 2015

Although the link between activity in the nuclei of galaxy and galactic mergers has been under scrutiny for several years, it is still unclear to what extent and for which populations of active galaxies merger-triggered activity is relevant. The environments of AGN allow an indirect probe of the past merger history and future merger probability of these systems, suffering less from sensitivity issues when extended to higher redshifts than traditional morphological studies of AGN host galaxies. Here we present results from our investigation of the environment of radio selected sources out to a redshift z=2. We employ the first data release J-band catalog of the new near-IR Infrared Medium-Deep Survey (IMS), 1.4 GHz radio data from the Faint Images of the Radio Sky at Twenty-cm (FIRST) survey and a deep dedicated VLA survey of the VIMOS field, covering a combined total of 20 sq. degrees. At a flux limit of the combined radio catalog of 0.1 mJy, we probe over 8 orders of magnitude of radio luminosity. Using the second closest neighbor density parameters, we test whether active galaxies inhabit denser environments. We find evidence for a sub-population of radio-selected AGN that reside in significantly overdense environments at small scales, although we do not find significant overdensities for the bulk of our sample. We show that radio-AGN in the most underdense environments have vigorous ongoing star formation. We interpret these results in terms of the triggering and fuelling mechanism of radio-AGN.

• 천문학회지
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• 제37권5호
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• pp.447-454
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• 2004

During the hierarchical formation of large scale structure in the universe, the progressive collapse and merging of dark matter should inevitably drive shocks into the gas, with nonthermal particle acceleration as a natural consequence. Two topics in this regard are discussed, emphasizing what important things nonthermal phenomena may tell us about the structure formation (SF) process itself. 1. Inverse Compton gamma-rays from large scale SF shocks and non-gravitational effects, and the implications for probing the warm-hot intergalactic medium. We utilize a semi-analytic approach based on Monte Carlo merger trees that treats both merger and accretion shocks self-consistently. 2. Production of $^6Li$ by cosmic rays from SF shocks in the early Galaxy, and the implications for probing Galaxy formation and uncertain physics on sub-Galactic scales. Our new observations of metal-poor halo stars with the Subaru High Dispersion Spectrograph are highlighted.

• 한국정보처리학회논문지
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• 제5권10호
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• pp.2615-2626
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• 1998

본 논문에서는 방향성 그래프인 Rotator 그래프와 Faber-Moore 그래프를 병합한 새로운 상호 연결망으로 RFM그래프를 제안하고, RFM그래프에 대하여 고장 허용도, 라우팅 알고리즘, 노드 중복 없는 싸이클, 방송 알고리즘을 분석한다. 또한 2차원 토러스, Strar 그래프, Bubblesort 그래프를 RFM 그래프에 연장비율(dilation) 2와 확장비율(expansion)1에 임베딩하는 방법을 제시한다.

• 천문학회보
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• 제35권2호
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• pp.39.2-39.2
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• 2010

We have investigated the evolution of the galaxy morphology in the hierarchical universe taking advantage of Semi-Analytic Model (SAM). It is well known that the galaxy morphology is related to the dynamical and the chemical evolution. This implies that we need to understand overall physical processes in the galaxy to reproduce its morphology. Thus we implemented gradual hot gas stripping of satellite galaxies in a galaxy cluster and recycling of stellar mass losses into our model in order to describe star formation rate of galaxies accurately. To morphologically classify galaxies, the evolution of disc and bulge components is traced carefully. We compute our models based on the dark matter halo merger trees generated by N-body simulations as well as the Extended Press-Schechter (EPS) formalism. We present morphological differences caused by the use of different merger trees.

• 천문학회보
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• 제42권1호
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• pp.51.1-51.1
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• 2017

The galaxy cluster Abell 115 shows ongoing merger features, which suggest that it might be in an intermediate phase of dynamical evolution. As merging clusters often show, the characteristic hints of A115's merging activities include radio relics, double X-ray peaks, and large offsets between the cluster member galaxies and the X-ray distributions. To constrain the exact stage of the merger, it is necessary to obtain its dark matter distribution. In this study, we carry out a precision weak lensing study of this interesting system based on Subaru images. We present our mass reconstruction together with descriptions on our core procedure of the analysis: Subaru data reduction, galaxy shape measurement, and source selection. We find that Abell 115 consists of two massive dark matter clumps, which closely follow the cluster galaxies. Our weak lensing mass estimate is a few factors lower than the published dynamical mass obtained from velocity dispersion. This large mass discrepancy may be attributed to a significant departure from dynamical equilibrium.

• 천문학회보
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• 제45권1호
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• pp.36.3-37
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• 2020

Recent observation of the neutron star merger event, GW170817, through both gravitational wave (GW) and electromagnetic wave (EM) observations opened a new way of exploring the universe, namely, multi-messenger astronomy (MMA). One of the keys to the success of MMA is a rapid identification of EM counterpart. We will introduce GW follow-up observation project in Korea for hunting GW EM counterpart rapidly and its strategy for prioritization of GW source host galaxy candidates. Our method relies on recent simulation results regarding plausible properties of GW source host galaxies and the low latency localization map from LIGO/Virgo. We will show a test result for both binary neutron star merger events using previous event and describe observing strategy with our facilities for GW events during the ongoing LIGO/Virgo O3 run. Finally, we report the results of optical/NIR follow-up observation of GW190425, the first neutron.

• 경영과정보연구
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• 제35권2호
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• pp.83-97
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• 2016

본 연구에서는 우리나라의 현행 합병 세제 및 자산조정계정의 산정방식의 고찰을 통하여 우리나라의 합병에 대한 규정을 살펴보고 향후 기업구조조정 세제가 정비되어야 할 바를 조망하고자 하였다. 특히 2010년 개정된 자산조정계정의 의미 및 사후 관리 규정의 현황과 문제점을 집중적으로 부각하였다. 우리나라의 합병과 관련된 관련 법규 및 세제는 초창기보다는 여러 가지 측면에서 비약적인 발전을 거듭했음에도 불구하고 아직까지 개선의 여지가 있는 부분이 많이 남아있으며, 법 규정이 미비한 부분을 이용한 조세회피가 가능한 부분이 있어 본 연구에서 개선방안을 제시해 보았다. 첫째, 자산조정계정은 실무상의 회계처리 및 세무조정의 복잡성뿐만 아니라 이를 일정 기간 동안 사후관리 해야 한다는 어려움도 있다. 만약 기업회계의 시가승계 방식을 세법도 그대로 준용한다면 복잡한 자산조정계정의 필요성도 사라지게 된다. 둘째, 합병법인이 지배주주 등인 경우에는 2년 내 포합주식을 일정액 이상 초과 취득한 경우에는 주식교부비율 미충족이라는 문제 때문에 과세이연을 받을 수가 없어서 기업구조조정을 2년이 경과한 시점 이후에나 추진해야 한다는 문제점이 있다. 이러한 현실적 문제를 고려하여 포합주식비율을 현재보다 더욱 완화할 필요가 있다. 마지막으로, 합병 후 사후관리 규정을 현행 2년에서 5년으로 강화해야 할 것이다. 이는 법인세법상에서 고유목적사업준비금이나 일시상각충당금의 설정에 대한 사후관리 요건이 5년으로 규정되어 있기 때문이기도 하다. 또한 주식보유요건과 사업의 계속성 요건도 별도의 규정을 마련하여 사후관리의 요건을 강화할 필요가 있다. 본 연구는 합병관련 정책입안자들 뿐만 아니라 실무에서 합병 관련 회계 및 세무처리를 하는 실무자들에게도 적격합병의 요건을 갖추어 과세이연을 실현할 수 있는 구체적인 요건을 제시한다는데 연구의 목적 및 필요성을 발견할 수 있다. 또한 현행의 자산조정계정이 앞으로 어떤 방향으로 합리적으로 개선 및 보완이 필요한지에 대한 방안을 제시했다는 점에서 공헌점 및 시사점을 찾을 수 있다.

• 천문학논총
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• 제30권2호
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• pp.331-333
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• 2015

Gravitational interactions - mergers and fly-by encounters - between galaxies play a key role as the drivers of their evolution. Here we perform a cosmological N-body simulation using the tree-particle-mesh code GOTPM, and attempt to separate out the effects of mergers and fly-bys between dark matter halos. Once close pair halos are identified by the halo finding algorithm PSB, they are classified into mergers ($E_{12}$ < 0) and fly-by encounters ($E_{12}$ > 0) based on the total energy ($E_{12}$) between two halos. The fly-by and merger fractions as functions of redshift, halo masses, and ambient environments are calculated and the result shows the following.(1) Among Milky-way sized halos ($0.33-2.0{\times}10^{12}h^{-1}M{\odot}$), $5.37{\pm}0.03%$ have experienced major fly-bys and $7.98{\pm}0.04%$ have undergone major mergers since z ~ 1; (2) Among dwarf halos ($0.1-0.33{\times}10^{12}h^{-1}M{\odot}$), $6.42{\pm}0.02%$ went through major fly-bys and $9.51{\pm}0.03%$ experienced major mergers since z ~ 1; (3) Milky-way sized halos in the cluster environment experienced fly-bys (mergers) 4-11(1.5-1.7) times more frequently than those in the field since z ~ 1; and (4) Approaching z = 0, the fly-by fraction decreases sharply with the merger fraction remaining constant, implying that the empirical pair/merger fractions (that decrease from z ~ 1) are in fact driven by the fly-bys, not by the mergers themselves.

• 천문학회보
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• 제42권1호
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• pp.30.1-30.1
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• 2017

In the hope to detect low-surface brightness features (${\mu}_{r^{\prime}}{\sim}27\;mag\;arcsec^{-2}$), we carried out KASI-Yonsei Deep Imaging Survey for Clusters (KYDISC) targeting 14 local clusters at 0.016 < z < 0.145 using Magellan/IMACS telescope and CFHT/MegaCam. Out of 1450 cluster galaxies, 18% of galaxies show the signatures of galaxy mergers. We explore merger-driven changes from various point-of-view. We first examine color-magnitude relations, and find that galaxies related to recent mergers are populated more on blue color than their counterparts. Besides, we find the extremely low frequency of mergers on low-mass red-sequence galaxies, suggesting a migration of red galaxies into the green-valley region through merger-driven star-formation. We also study the mass-size relation of our sample, finding a larger galaxy size in galaxies related to recent mergers. Our results suggest that mergers can simultaneously change properties of galaxies, making outliers on galactic scaling relations.