• Journal of Astronomy and Space Sciences
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• v.14 no.1
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• pp.1-17
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• 1997

The results of a restricted numerical simulation for the color gradients within globular clusters have been presented. The standard luminosity function of M3 and Salperter's initial mass functions were used to generate model clusters as a fundamental population. Color gradients with the sample clusters for both King and power law cusp models of surface brightness distributions are discussed in the case of using the standard luminosity function. The dependence of color gradients on several parameters for the simulations with Salpter's initial mass functions, such as slope of initial mass functions, cluster ages, metallicities, concentration parameters of King model, and slopes of power law, are also discussed. No significant radial color gradients are shown to the sample clusters which are regenerated by a random number generation technique with various parameters in both of King and power law cusp models of surface brightness distributions. Dynamical mass segregation and stellar evolution of horizontal branch stars and blue stragglers should be included for the general case of model simulations to show the observed radial color gradients within globular clusters.

• Journal of The Korean Astronomical Society
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• v.29 no.2
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• pp.269-278
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• 1996

We present the color-magnitude diagrams (CMD) of more than 24,000 stars in the field of an intermediate age open cluster M11, based on wide field CCD imaging. The morphology of the CMDs varies strikingly as the distance from the center of the cluster increases. From the surface number density analysis, we confirm the mass segregation effect in this cluster: the bright, massive stars are centrally more concetrated than the faint, low mass stars. The slope of the field-corrected surface density with respect to magnitude progressively increases as the radius increases, up to r = 5'. Most of the field stars in or near the cluster main sequence band and in the bright part of the red stars in the CMDs appear to be nearly at the same distance as M11, and they are considered to be the major component of disk stars in the Sagittarius-Carina arm.

• Journal of The Korean Astronomical Society
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• v.39 no.3
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• pp.57-71
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• 2006

We investigated the structural parameters of a sample of 30 dwarf galaxies(15 dEs and 15 dS0s) in the Virgo Cluster using i-band images from the Sloan Digital Sky Survey Data Release 4. Among 28 galaxies for which surface brightness profiles were derived from ellipse fittings, 23 galaxies had a single component that was adequately described by a generalized $S\acute{e}rsic$ function with a shape parameter ranging from n=0.5 to 2, while 5 galaxies(2 dEs and 3 dS0s) had bulge and disk components that were fitted by a generalized $S\acute{e}rsic$ function and an exponential function, respectively. Since the majority of dwarf galaxies in the present sample had a single component, it seems likely that genuine dS0 galaxies that have disk and bulge components are quite rare in the Virgo Cluster. The similarity in structural parameters of genuine dS0 galaxies in the Virgo Cluster with those of Magellanic-type galaxies implies that the progenitors of dwarf lenticular galaxies in the Virgo Cluster were most likely Magellanic-type galaxies if dS0s are harassed late-type spirals.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.1
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• pp.56.2-56.2
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• 2012

We present a study of the asymptotic giant branch (AGB) contribution to the total Ks band luminosity of star clusters in the Large Magellanic Cloud (LMC) as a function of age. AGB stars, a representative intermediate-age population, are a strong source of NIR to MIR emission so that they are a critical component for understanding the near-to-mid infrared observation of galaxies. Current calibration of IR emission in evolutionary population synthesis (EPS) models for galaxies is mainly based on a small number of LMC star clusters. However, each LMC star cluster with intermediate age contains only a few AGB stars so that it suffers from a stochastic effect. Therefore a large number of them are needed for solid calibration of the EPS models. We study physical properties of a large number of LMC star clusters to estimate the Ks band luminosity fraction of AGB stars in star clusters as a function of age. We discuss the stochastic effect in calibrating models, and the importance of this calibration for studying the evolution of not only nearby galaxies but also of high-z galaxies.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.2
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• pp.30.2-30.2
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• 2015

Abell 2744 is a giant merging cluster, called the Pandora's Cluster, at the redshift of z=0.308 (corresponding to a distance of 1270 Mpc). Taking the advantage of the deep high resolution images in the Hubble Frontier Field program, we study the properties of compact stellar systems including globular clusters and ultracompact dwarfs (UCDs) as well as dwarf galaxies in this cluster. We find a rich population of globular clusters and UCDs in Abell 2744. The spatial distribution of these objects is consistent with the mass map derived from lensing analysis, while showing a significant offset from the X-ray map of hot gas. The faint end of the luminosity function of the galaxies in the red sequence is fit by a flat slope, showing no faint upturn. We discuss these finding in relation with the origin of UCDs, formation of red sequence dwarf galaxies, and formation of the Pandora's cluster.

• Journal of The Korean Astronomical Society
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• v.38 no.3
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• pp.345-355
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• 2005

We present a photometric study of the star cluster system in the merging galaxy NGC 1487, based on the BI photometry obtained from the F450W and F814W images in the HST /WFPC2 archive data. We have found about 560 star cluster candidates in NGC 1487, using the morphological parameters of the objects. We have investigated several photometric characteristics of the clusters: color-magnitude diagrams (CMDs), color distribution, spatial distribution, age, size and luminosity function. The CMD of the bright clusters with 18.5 < B < 24 mag in NGC 1487 shows three major populations of clusters: a blue cluster population with $(B-I){\le}0.45$, an intermediate-color cluster population with $0.45<(B-I){\le}1.55$, and a red cluster population with (B - I) > 1.55. The intermediate-color population is the most dominant among the three populations. The brightest clusters in the blue and intermediate- color populations are as bright as $B{\approx}18mag$ ($M_B{\approx}-12mag$), which are three magnitudes brighter than those in the red population. The blue and intermediate-color clusters are strongly concentrated on the bright condensations, while the red clusters are relatively more scattered over the galaxy. The CMD of these clusters is found to be remarkably similar to that of the clusters in the famous interacting system M51. From this we suggest that the intermediate-color clusters were, probably, formed during the merging process which occurred about 500 Myrs ago.

• Bulletin of the Korean Space Science Society
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• 1999.09a
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• pp.34-34
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• 1999

No Abstract, See Full Text

• The Bulletin of The Korean Astronomical Society
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• v.46 no.1
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• pp.47.1-47.1
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• 2021

Cosmic Dawn III (CoDa III) is the last of the series of simulations of the reionization of the Local Group, the galaxy cluster including the Milky Way and the M31. The simulation is based on the constrained initial condition, N-body and hydrodynamic simulation of structure formation, modelling of galaxy formation, calculation of radiation transfer, and calibration against the observed high-redshift galaxy luminosity function. We present various physical properties we observed and important lessons that could stimulate future observations.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.2
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• pp.63.2-63.2
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• 2016

One of the well-known problems in the lambda cold dark matter (${\Lambda}CDM$) models is a missing satellite problem. The slope of the mass function of low mass galaxies predicted by ${\Lambda}CDM$ models is much steeper than that based on the luminosity function of dwarf galaxies in the local universe. This implies that the model prediction is an overestimate of low mass galaxies, or that the current census of dwarf galaxies in the local universe may be an underestimate of dwarf galaxies. Previous studies of galaxy luminosity functions to address this problem are based mostly on the sample of galaxies brighter than Mv ~ -10 in the nearby galaxies. In this study we try to search for ultra-faint galaxies (UFDs), which are much fainter than those in the previous studies. We use multi-field HST ACS images of M60 in the archive. M60 is a giant elliptical galaxy located in the east part of the Virgo cluster, and hosts a large population of globular clusters and UCDs. Little is known about the dwarf galaxies in this galaxy. UFDs are much fainter, much smaller, and have lower surface brightness than normal dwarf galaxies so HST images of massive galaxies are an ideal resource. We present preliminary results of this search.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.1
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• pp.53.3-54
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• 2016

We present a preliminary result of the Fornax cluster survey as a part of the KMTNet Intensive Nearby Southern Galaxy Group Survey (KINGS). We discovered about 200 new dwarf galaxy candidates from the survey of the $8^{\circ}{\times}6^{\circ}$ area around the Fornax cluster. They have magnitudes ranging from V=17.5 to 22 mag (Mv = -13.8 to -9.3), and they are almost complete to V = 20 mag. Surface brightness profiles of most of these galaxies are fit well by a Sersic law with n ~ 1.0. Structural parameters of these galaxies follow well the scaling relations of dwarf galaxies in the fundamental plane. The color-magnitude diagram of these galaxies shows that they are mostly located at the faint end of the red sequence, indicating that they are the probable member of the Fornax cluster. We also derive a luminosity function of the Fornax cluster by combining the new galaxies with the known galaxies in the previous catalogs. We will discuss the future of the KINGS-Fornax.