• The Bulletin of The Korean Astronomical Society
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• v.36 no.1
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• pp.55.1-55.1
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• 2011

We investigate dynamical evolution of gas in barred galaxies using a high-resolution, grid-based hydrodynamic simulations on two-dimensional cylindrical geometry. Non-axisymmetric gravitational potential of the bar is represented by the Ferrers ellipsoids independent of time. Previous studies on this subject used either particle approaches or treated the bar potential in an incorrect way. The gaseous medium is assumed to be infinitesimally-thin, isothermal, unmagnetized, and initially uniform. To study the effects of various environments on the gas evolution, we vary the gas sound speed as well as the mass of a SMBH located at the center of a galaxy. An introduction of the bar potential produces bar substructure including a pair of dust lane shocks, a nuclear ring, and nuclear spirals. The sound speed affects the position and strength of the bar substructure significantly. As the sound speed increases, the dust lane shocks tend to move closer to the bar major axis, resulting in a smaller-size nuclear ring at the galactocentric radius of about 1 kpc. Nuclear spirals that develop inside a nuclear ring can persist only when either sound speed is low or in the presence of a SMBH; they would otherwise be destroyed by the ring material with eccentric orbits. The mass inflow rates of gas toward the galactic center is also found to be proportional to the sound speed. We find that the sound speed should be 15 km/s or larger if the mass inflow rate is to explain nuclear activities in Seyfert galaxies.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.1
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• pp.63.2-63.2
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• 2011

We present a photometric study of star clusters in three nearby barred spiral galaxies NGC 1300, NGC 1672 and NGC 6217. We use the Hubble Heritage CCD images taken with Advanced Camera for Surveys (ACS) of Hubble Space Telescope (HST) in several filters. We have selected hundreds of star clusters with V $\leq$ 24 mag in each galaxy, based on the morphological parameters and visual inspection. Most of the blue star clusters with B-V $\leq$ 0.5 are strongly concentrated in spiral arms. A significant fraction of these star clusters are distributed in ansae (the joint between spiral arms and bar structure). Some of the blue star clusters are also found in the nuclear starburst region, especially in NGC 1672. A small number of star clusters are found in the bar region. In contrast, the red star clusters with B-V < 0.5 are relatively uniformly located over the entire field of galaxy, and show some central concentration around the bulge. We discuss the physical properties of these star clusters with the expected results from simulations.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.1
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• pp.60.2-60.2
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• 2011

Galactic bars are supposed to be a channel of gas inflow to the galactic center and thus possibly help nuclear star-formation and AGN activities. However, previous studies based on small local samples did not agree with this expectation. We find it necessary to examine the expectation using a large sample and so investigate the effects of bar structures on galactic nuclear activities, based on the Sloan Digital Sky Survey (SDSS) DR7. We used 6,348 late-type galaxies brighter than Mr = -19.0 in the redshift range $0.01{\leq}z{\leq}0.05$. Late-type galaxies are visually classified into barred or unbarred galaxies using SDSS color composite images. We compare the fractions of galaxies showing star-formation and AGN activities among barred and unbarred galaxies as a function of optical color, stellar mass, and black-hole mass. We have found that bar enhances nuclear star-formation activity on galaxies having low stellar mass, and low black-hole mass. This effect is stronger in redder galaxies. In the case of AGN, bar effects are higher in intermediate-mass galaxies. Bars also have an effect on the strength(!) of the star-formation and AGN activity in our sample as well. Thus, it seems that nuclear activities are powered by gas inflow from galactic bar structures perhaps not always but under certain conditions.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.34.1-34.1
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• 2019

To study the formation and evolution of stellar bars and gaseous nuclear rings in barred galaxies in realistic environments, we run fully self-consistent three-dimensional simulations of isolated disk galaxies. We consider two groups of models with cold or warm disks that differ in the radial velocity dispersion. We also vary the gas fraction of the disks. We found that a bar forms earlier and more strongly as the gas fraction increases in the cold disks, while the gas delays the bar formation in the warm disks. The bar formation enhances a central mass concentration which in turn weakens the bar strength temporarily, after which the bar regrows to become stronger in a model with a smaller gas fraction in both cold and warm disks. Although all bars rotate fast in the beginning, they rapidly turn to slow rotators. Gas infalling to the central region forms a dense star-forming nuclear ring. The ring size is very small when it first forms and grows over time. The ring star formation is episodic and bursty due to star formation feedback, and has a good correlation with the mass inflow rate to the ring. Some expanding shells produced by star formation feedback are sheared out in the bar regions and collide with dust lanes to appear as filamentary interbar spurs.

• Proceedings of the Korean Information Science Society Conference
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• 2001.10b
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• pp.382-384
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• 2001

본 논문에서는 홍채의 특징을 효율적으로 추출하기 위한 접근 방법으로서, 웨이블릿 기반의 다해상도 분석 기법을 홍채영상에 적용한 결과에 대하여 소개하고자 한다. 입력장치인 카메라로부터 획득된 사람의 눈 영상에서 처리 대상인 홍채영역 만을 분리 추출한 후, 홍채 특징을 압축적이고 효과적으로 표상하기 위하여 2D 다해상도 웨이블릿 변환을 홍채영상에 적용하는 기법과 실제적인 응용을 위하여 등록된 데이터와 미지의 데이터 사이의 유사도를 측정하는 효율적인 기법을 연구한다. 이러한 기법들을 홍채 인식 시스템에 적용함으로써 처리속도 및 인식률 향상 등으로 고성능의 홍채인식시스템을 구현할 수 있었다.

• Journal of The Korean Astronomical Society
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• v.16 no.1
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• pp.1-5
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• 1983

Four HII regions of the Sd galaxy NGC 7793 were observed using AAT/IPCS. From these spectra we determined abundances of the elements using observed emission lines and electron temperatures. The calculated abundances show that this galaxy does not show any significant radial abundance gradient. The mean oxygen abundance is very much like the Orion nebulae and the nitrogen abundance is similar to the late type barred spiral galaxy NGC 1313.

• Journal of Astronomy and Space Sciences
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• v.9 no.1
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• pp.1-10
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• 1992

Isophote map and luminosity profile of the barred spiral galaxy NGC 7755 are obtained from PDS scanning of PAL 0-471 plate. From the isophote map, NGC 7755 can be classified SBbc(r) with asymmetric bar ring. We get several physical parameters $({M_T}^\circ,U(R)_{CB},U(R)_{CD},D/B,C_{jj},M/L)$ of NGC 7755 from the analysis of the luminosity distribution.

• The Bulletin of The Korean Astronomical Society
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• v.38 no.2
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• pp.39.1-39.1
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• 2013

We use high-resolution hydrodynamic simulations to study nonlinear gas responses to imposed non-axisymmetric stellar potentials in barred-spiral galaxies. The gas is assumed to be infinitesimally thin, isothermal, and unmagnetized. We consider various spiral-arm models with differing strength and pattern speed, while fixing the bar parameters. We find that the extent and shapes of spiral shocks as well as the related mass drift depend rather sensitively on the pattern speed. In models where the arm pattern is rotating more slowly than the bar, the gaseous arms extend from the bar ends all the way to the outer boundary, with a pitch angle slightly smaller than that of the stellar counterpart. The arms drive mass inflows at a rate of ${\sim}0.5-2.5M{\odot}/yr$ to the bar region to which the shock dissipation, external torque, and self-gravitational torque contribute about 50%, 40%, and 10%, respectively. About 85% of the inflowing mass is added to bar substructures such as an inner ring, dust lanes, and a nuclear ring. while the remaining 15% encircles the bar region. On the other hand, models where the arms corotate with the bar exhibit mass outflows, rather than inflows, over most of the arm region. In these models, spiral shocks are much more tightly wound than the stellar arms and cease to exist in the region where $M{\bot}/sinp*{\geq}25-40$, where $M{\bot}$ denotes the Mach number of a rotating gas perpendicular to the arms with pitch angle p*. We demonstrate that the distributions of line-of-sight velocities and densities can be a useful diagnostic tool to distinguish if the arms and bar corotate or not.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.75.1-75.1
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• 2011

We investigate the connection between the presence of bars and AGN activity, using a volume-limited sample of ~6,000 late-type galaxies with axis ratio b/a > 0.6 and $M_r=-19.5+5logh$ at low redshift (0.02 < z ${\leq}$ 0.055), selected from Sloan Digital Sky Survey Data Release 7. Although bars are believed to play an important role in fueling AGNs, it is still an open question whether AGN activity is connected with the presence of bars. We find that the bar fraction in AGN-host galaxies (44.1%) is 2.5 times higher than in non-AGN galaxies (17.6%), implying an AGN-bar connection. However, this trend is simply caused by the fact that AGN-host galaxies are on average more massive and redder than non-AGN galaxies since the bar fraction increases with u-r color and velocity dispersion. When AGN-host and non-AGN galaxies with fixed u-r color and velocity dispersion are compared, the excess of bar fraction in AGN-host galaxies disappears. Among AGN-host galaxies we find no strong difference of the Eddington ratio distributions between barred and non-barred systems. These results indicate that AGN activity is not directly connected with the presence of bars.

• Korean Institute of Interior Design Journal
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• no.28
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• pp.51-59
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• 2001

This Study tried to approach with a new Point of view about Green Design that had been studied on just Aesthetics and Function and it focused on creating a pleasant environment In the Interiors combing with Horticultural therapy as advanced study in Green Design. This study is barred on understanding that nature, human and space should continue to coexist through realizing relationship between nature and human and overcoming denaturalization and dehumanization and have an opportunity to know what a pleasant space for human is. Although pleasant space can be made by many different methods, this study start from the thought that a space with plants is the best to satisfy human's basic emotion. The method of study is through research and analysis with many kinds of references and examples, and then the results were used to make design guide which introduces Green Amenity Space in residential space. The pleasant space that human pursuits should be the human-centered space as well as the space giving them mental and physical satisfaction beyond space with just function and beauty. Therefore Green Amenity Space is the best space with which human is familiar.