• The Bulletin of The Korean Astronomical Society
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• v.42 no.2
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• pp.75.2-75.2
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• 2017

We Investigate dust stripping of Virgo cluster galaxies that are known to suffer HI gas stripping. The gas stripping phenomena of these galaxies may result from either ram pressure induced by the hot intracluster medium or gravitational tidal interactions between galaxies. While much efforts have been made to directly detect gas removed from cluster galaxies, the spatial distributions of dust, which should also be affected, are hardly known. Several previous studies have tried to directly detect the morphology of gas or dust using radio or infrared observations, but such approaches are hard to widely apply because of the limit of observational resolution and sensitivity. In this study, we try a different approach using optical data: measuring the background galaxy reddening by the dust stripped from the Virgo cluster members. Based on optical color excess maps of the background galaxies, we compare the ambient dust distribution with the HI morphology of the Virgo galaxies. We discuss how efficiently dust stripping can be detected with this method and how the stripped dust is associated with the removed gas according to HI gas stripping stage over the sample.

• Journal of The Korean Astronomical Society
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• v.38 no.2
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• pp.245-248
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• 2005

We present mm observations with the IRAM 30m radiotelescope of the HCN (J=1-0) and HCO+ (J=1-0) emission lines from Giant Moleculat Clouds (GMC) in the disk of the Andromeda Galaxy, The selected GMC targets have various morphology and environments, including locations within spiral arms or in interarm regions and with galactocentric radii ranging from 2.4 to 15.5 kpc over the disk. The radial distributions of the ratios HCN/CO and HCO+ /CO are discussed and their values are compared to other galaxies.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.2
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• pp.29.2-29.2
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• 2015

Interactions such as mergers and flybys play a fundamental role in shaping galaxy morphology. We used the Horizon Run 4 cosmological N-body simulations to study the aligments of spins and shapes of interacting haloes as a function of the halo mass and large-scale density. Interactions preferentially occur in the plane of rotation, and in the direction of the major axis of prolate haloes, and the trajectories are preferentially radial and prograde. We found a very strong alignment of the shapes already at redshift as high as 4. The spins are initially unaligned or even anti-aligned, and become more and more aligned as the redshift decreases. The alignment signals are stronger and evolve more at lower densities, and mass plays a secondary role.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.2
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• pp.35.3-35.3
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• 2015

The central molecular zone (CMZ) is a region of rich molecular gas located in the inner few hundred parsecs in barred spiral galaxies. We study the size and morphology evolution of the CMZ of Milky Way-like galaxies both in isolation and in interaction by using N-body/hydrodynamic simulations. Specifically, we examine the gas flows and star formation activities in the central region of the galaxies. We focus in particular on the effects of galaxy interactions, including flybys and minor mergers, on the evolution of the CMZ.

• Journal of The Korean Astronomical Society
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• v.49 no.6
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• pp.239-253
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• 2016

We determined the warp parameters of 192 warped galaxies which are selected from 340 edge-on galaxies using color images as well as r-band isophotal maps. We derive the local background density (${\Sigma}_n$) to examine the dependence of the warp amplitudes on the galaxy environment. We find a clear trend that strongly warped galaxies are likely to be found in high density regions where tidal interactions are supposed to be frequent. However, the correlation between ${\alpha}_{\omega}$ and ${\Sigma}_n$ is too weak for weakly warped galaxies (${\alpha}_{\omega}$ < $4^{\circ}$) and the cumulative distributions of weakly warped galaxies are not significantly different from those of galaxies with no detectable warps. This suggests that tidal interactions do not play a decisive role in the formation of weak warps.

• Publications of The Korean Astronomical Society
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• v.14 no.1
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• pp.1-8
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• 1999

We performed VRI CCD surface photometry of three spiral galaxies of HCG10 in order to understand the effect of interactions in the compact group. The morphology of the largest member NGC 536 seems to be normal but its bulge is thought to be of an oblate spheroid. The central surface brightness of the disk of NGC 536 is much fainter than that of disks of nearby spiral galaxies. The morphologies of NGC 531 and NGG 542 appear to be affected by interactions which lead to a warped disk in NGC 531 and a slightly bent disk in NGC 542. NGC 531 have a boxy bulge and a Freeman Type II disk both of which strongly suggest the presence of a bar in the galaxy. There is a break in the slope of the luminosity profile of NGC 542 which is dominated by the disk component.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.2
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• pp.40.3-41
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• 2016

Previous HI survey data have shown that the central HI gas in the Milky Way that resides within ~1.5 kpc of the Galactic Centre (GC) is tilted by ${\sim}15^{\circ}$ with respect to the Galactic plane. Although several models, such as a tilted disk model, have been suggested to interpret the observed morphology of the HI layer, it is still unknown what causes and how it preserves its tilted structure. We study the behavior of a gas disk near the GC using an N-body / SPH code. Our galaxy model includes four components; nuclear bulge, bulge, disk and halo. We construct a HI model whose radius is 1.3 kpc, scale height is 100 pc and mass is $3.6{\times}10^6M_{\odot}$. We also assume that the gas disk is initially tilted $30^{\circ}$ with respect to the Galactic plane. Here we report our simulation results and discuss the evolution of the tilted gas disk.

• Journal of The Korean Astronomical Society
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• v.29 no.spc1
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• pp.49-51
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• 1996

New population synthesis models, with the effects of metallicity spread and the horizontal-branch (HB) morphology, provide a way to break the well-known age-metallicity degeneracy in the analysis of the integrated light of elliptical galaxies. Our models suggest that the far- UV radiation of these systems is dominated by a minority population of metal-poor, hot HB stars and their post-HB progeny, while the optical radiation is dominated by a metal-rich population. The systematic variation of UV upturn depends on the contribution from metal-poor, hot HB stars and their post-HB progeny, which in turn depends on the ages of old stellar populations in galaxies. Our result implies a prolonged epoch of galaxy formation, in the sense that more massive galaxies (in denser environments) formed first. Our models also suggest that the strenghth of H$\beta$ index is strongly affected by HB stars, and hence previous age estimation without detailed modeling of the HB would underestimate the ages of ellipticals by $\~$7 Gyr.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.73.1-73.1
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• 2011

An understanding of the ultraviolet (UV) properties of nearby galaxies is essential for interpreting images of high redshift systems. In this respect, the prediction of optical-band morphologies at high redshifts requires UV images of local galaxies with various morphologies. We present the simulated optical images of galaxies at high redshifts using diverse and high-quality UV images of nearby galaxies obtained through the Galaxy Evolution Explorer (GALEX). We measured CAS (concentration, asymmetry, clumpiness) as well as Gini/M20 parameters of galaxies at near-ultraviolet (NUV) and simulated optical images to quantify effects of redshift on the appearance of distant stellar systems. We also discuss the change of morphological parameters with redshift.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.2
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• pp.53.3-53.3
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• 2019

Recent work by Ravanbakhsh et al. (2017), Mathuriya et al. (2018) showed that convolutional neural networks (CNN) can be trained to predict cosmological parameters from the visual shape of the large scale structure, i.e. the filaments, clusters and voids of the cosmic density field. These preliminary works used the dark matter density field at redshift zero. We build upon these works by considering realistic mock galaxy catalogues that mimic true observations. We construct light-cones that span the redshift range appropriate for current and near future cosmological surveys such as LSST, EUCLID, WFIRST etc. In summary, we propose a novel multi-image input CNN to track the evolution in the morphology of large scale structures over cosmic time to constrain cosmology and the expansion history of the Universe.