• Journal of The Korean Astronomical Society
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• v.36 no.3
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• pp.223-239
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• 2003

It is now a well established fact that galaxies undergo significant morphological transformation during their lifetimes, manifesting as an evolution along the Hubble sequence from the late to the early Hubble types. The physical processes commonly believed to be responsible for this observed evolution trend, i.e. the major and minor mergers, as well as gas accretion under a barred potential, though demonstrated applicability to selected types of galaxies, on the whole have failed to reproduce the most important statistical and internal properties of galaxies. The secular evolution mechanism reviewed in this paper has the potential to overcome most of the known difficulties of the existing theories to provide a natural and coherent explanation of the properties of present day as well as high-redshift galaxies.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.1
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• pp.54.1-54.1
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• 2011

Formation of self-gravitating gas clouds and hence stars in galaxies is a consequence of both thermal and dynamical evolution of a gaseous medium. Using hydrodynamics simulations including cooling and heating explicitly, we follow simultaneously thermal and dynamical evolution of galactic gas disks to study dynamics and structures of galactic spiral shocks with thermal instability and regulation of the star formation rates (SFRs). We first perform one-dimensional simulations in direction perpendicular to spiral arms. The multiphase gas flows across the arm soon achieve a quasi-steady state characterized by transitions from warm to cold phases at the shock and from cold to warm phases in the postshock expansion zone, producing a substantial fraction of intermediate-temperature gas. Next, we allow a vertical degree of freedom to model vertically stratified disks. The shock front experiences unsteady flapping motions, driving a significant amount of random gas motions, and self-gravity promotes formation of bound clouds inside spiral arms. Finally, we include the star formation feedback in both mechanical (due to supernova explosion) and radiative (due to FUV heating by young stars) forms in the absence of spiral arms. At saturation, gravitationally bound clouds form via thermal and gravitational instabilities, which are compensated by disruption via supernova explosions. We find that the FUV heating regulates the SFRs when gas surface density is low, confirming the prediction of the thermal and dynamical equilibrium model of Ostriker et al. (2010) for star formation regulation.

• 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.

• Publications of The Korean Astronomical Society
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• v.27 no.4
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• pp.293-294
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• 2012

We established a separation scheme to distinguish galaxies from stars with the aid of AKARI/FIS color-color (CC) diagrams. In all the combinations of CC diagrams we can distinguish two separate clouds. It was shown that in all cases one of them contains more than 95% of galaxies and the other one, in most cases, consists in more than 80% of stars (Pollo et al., 2010). Currently we are looking into more detailed classifications. We are especially interested in separating different morphological types of galaxies, mainly within spiral galaxies. Moreover, we study the properties of infrared galaxies.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.1
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• pp.32.2-32.2
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• 2018

We present the structural parameters of ~ 910 dwarf elliptical-like galaxies in the local universe ($z{\lesssim}0.01$) derived from the r-band images of the Sloan Digital SKy Survey (SDSS). We examine the dependence of structural parameters on the morphological types (dS0, dE, dEbc, dSph, and dEblue) and the environment. There is not much difference in the structural parameters among the five subtypes but the mean surface brightness within the effective radius (<${\mu}e$>) of dSph galaxies is clearly different from that of other subtypes. The frequency of disk features such as spiral arm, bar, lens, and rings strongly depends on the morphology of dwarf elliptical-like galaxies with no disk features in dSph galaxies. The absence of disk features and the low surface brightness of dSph galaxies are thought to be closely related to their low mass which leads to different evolution from other subtypes of dwarf elliptical-like galaxies. Density Environments Using IMSNG.

• Bulletin of the Korean Space Science Society
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• 1994.09a
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• pp.43-43
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• 1994

No Abstract. See Full-text

• Bulletin of the Korean Space Science Society
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• 1998.10a
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• pp.20.1-20
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• 1998

No Abstract.See Full-text

• Bulletin of the Korean Space Science Society
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• 2001.11a
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• pp.56-56
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• 2001

• The Bulletin of The Korean Astronomical Society
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• v.24 no.1
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• pp.59-59
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• 1999

• The Bulletin of The Korean Astronomical Society
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• v.6
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• pp.7.3-7.3
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• 1981