• 한국지구과학회지
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• 제41권3호
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• pp.211-221
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• 2020

이 연구는 SDSS DR7의 적색이동(z)<0.05이고, 동시에 R_pet>6 arcsec, 단축과 장축의 비(b/a)>0.6인 외부은하 25,308개를 분류하고, 색 영상을 육안으로 조사하여 고리 모양의 구조를 가진 531개 은하를 선별했다. 이 은하들이 일차적 표본으로 사용되었고, 이 중 90개의 외부고리 은하 후보를 선택했다. 후보 은하의 u, g, r, i, z 영상에 대한 표면 측광으로부터 도출한 특성을 조사하여 최종으로 69개의 외부고리 은하를 결정했다. 외부고리 은하는 국부은하의 0.3%를 차지하는 것으로 나타났으며, 두 개의 환경 인자, 즉, 가장 가까운 은하까지의 투영 거리와 국부 배경 은하 밀도를 이용하여, 외부고리 은하의 환경 특성을 조사했다. 외부고리 은하의 환경이 다른 은하의 경우와 비교하여 눈에 띄는 차이의 결과는 보이지 않았다.

• 한국지구과학회지
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• 제43권5호
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• pp.579-590
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• 2022

본 연구는 데이터 과학의 과정에 따른 파이썬 기반의 외부고리 은하 영상 분석 알고리즘 개발을 목적으로 한다. 잠재적 사용자는 학생과 교사를 포함한 시민 과학자로 정하였다. 은하의 실제 데이터를 이용한 분류 연구는 IRAF 라는 전문 소프트웨어가 이용되고 있어 일반인이 접근하기에 한계가 있다. 이에 IRAF를 사용한 선행 연구의 결과와 비교 검증이 가능한 외부고리 은하를 분석 대상 천체로 정하여, 영상 분석 알고리즘을 개발하고 그 결과를 검증하였다. 검증 결과 총 69개의 외부고리 은하 중 50개(72.5%)가 IRAF 결과와 높은 일치를 보였다. 남은 19개(27.5%)는 시선 방향에 겹친 밝은 별의 존재 혹은 은하 내부의 약한 밝기로 인해 IRAF 결과와 다른 낮은 일치를 보였다. 보완 과정을 거친 최종 결과물은 공유 및 교육 자료의 활용도를 높이기 위해 전체 사용된 데이터와 알고리즘, 파이썬 코드 파일 및 사용 설명서를 GitHub에 탑재하였다.

• 천문학회보
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• 제41권2호
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• pp.39.2-40
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• 2016

The molecular gas surrounding an H II region is thought to be a place where star formation can be induced. Such triggered star formation can arise form the overpressurization of existing density enhancements or thought the collapse of a swept up layers of material. In this talk, We will discuss the results of a study of star-formation activity associated with the outer Galaxy ring-shaped H II regions KR 7, KR 81, KR 120 and KR 140 using archival Spitzer and WISE data along with the JHK observations. We used CO data cubes from the FCRAO and TRAO in order to define extent of the molecular cloud associated each HII region. Using the infrared data sets, We identified and classified YSO populations within each molecular cloud using measures such as the class I/II ratio and YSO spatial density. Along with this, one of the main question in the study of star formation is how protostar accrete material from their parent molecular clouds and observations of infall motions are needed to provide direct evidence for accretion. Combining our observation of the YSO population distribution with time scales associated with YSO evolution and HII expansion, we investigated the possible significance of triggered star formation in the molecular cloud surrounding each region.

• 천문학회보
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• 제37권1호
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• pp.38.2-38.2
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• 2012

We use two-dimensional high-resolution MHD simulations to investigate the effects of magnetic fields on the formation and evolution of such substructures as well as on the mass inflow rates to the galaxy center. We find that there exists an outermost x1-orbit relative to which gaseous responses to an imposed stellar bar potential are completely different between inside and outside. Inside this orbit, gas is shocked into dust lanes and infalls to form a nuclear ring. Magnetic fields are compressed in dust lanes, reducing their peak density. Magnetic stress removes further angular momentum of the gas at the shocks and leads to a smaller and more centrally distributed ring, resulting in the mass inflow rates larger, by more than two orders of magnitude, than in the unmagnetized counterparts. Outside the outermost x1-orbit, on the other hand, an MHD dynamo operates near the corotation and bar-end regions, efficiently amplifying magnetic fields. The amplified fields shape into trailing magnetic arms with strong fields and low density. The base of the magnetic arms have a thin layer in which magnetic fields with opposite polarity reconnect via a tearing-mode instability. This produces numerous magnetic islands with large density which propagate along the arms to turn the outer disk into a highly chaotic state.

• 천문학회보
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• 제37권1호
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• pp.72.2-72.2
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• 2012

We present the results of HI 21 cm line observations to explore the nature of the high-velocity (HV) HI gas at - 173${\circ}$, which appears as faint, wing-like, Hi emission that extends to velocities beyond those allowed by Galactic rotation in the low-resolution surveys. We designate this feature as Forbidden Velocity Wing (FVW) 172.8+1.5. Our high-resolution Arecibo HI observations show that FVW 172.8+1.5 is composed of knots, filaments, and ring-like structures distributed over an area of a few degrees in extent. These HV HI emission features are well correlated with the HII complex G173+1.5, which is composed of five Sharpless HII regions distributed along a radio continuum loop of size 4.4${\times}$3.4, or -138 pc ${\times}$ 107 pc, at a distance of 1.8 kpc. G173+1.5 is one of the largest star-forming regions in the outer Galaxy. The HV HI gas and the radio continuum loop seem to trace an expanding shell. Its derived HI parameters including large expansion velocity (55 km/s) imply the SNR interpretation. Hot xray emission is detected within the HII complex, which also supports its SNR origin. The FVW172.8+1.5 is most likely the products of a supernova explosion(s) within the HII complex, possibly in a cluster that triggered the formation of these HII regions.

• 천문학회지
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• 제31권2호
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• pp.161-171
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• 1998

We have mapped about 1.5 square degree regions of Lynds 1299, a well isolated dark cloud in the Outer Galaxy (l = $122^{\circ}$, b = $-7^{\circ}$), in the J = 1- 0 transition of $^{12}CO$ and $^{13}CO$ with the 13.7 m radio telescope at Taeduk Radio Astronomy Observatory (TRAO). We found that there are two velocity components in the molecular emission, at $V_{LSR} = -52 km S^{-1}$ (Cloud A) and -8.8 km $s^{-1}$ (Cloud B), respectively. We have derived physical parameters of two molecular clouds and discussed three different mass estimate techniques. We found that there are large discrepancies between the virial and LTE mass estimates for both clouds. The large virial mass estimate reflects the fact that both are not gravitationally bound. We adopt the mass of $5.6 {\times}10^3 \;M{\bigodot}$ for Cloud A and $1.2{\times}10^3 \;M{\bigodot}$) for Cloud B using conversion factor. Cloud A is found to be associated with a localized star forming site, and its morphology is well matching with that of far-infrared (FIR) dust emission. It shows a clear ring structure with an obvious velocity gradient. We suggest that it may be a remnant cloud from a past episode of massive star formation. Cloud B is found to be unrelated to Cloud A (d = 800 pc) and has no specific velocity structure. The average dust color temperature of the uncontaminated portion of Cloud A is estimated to be 24$\~$27.4 K. The low dust temperature may imply that there is no additional internal heating source within the cloud. The heating of the cloud is probably dominated by the interstellar radiation field except the region directly associated with the new-born B5 star. Overall, the dust properties of Cloud A are similar to those of normal dark cloud even though it does have star forming activity.