• The Bulletin of The Korean Astronomical Society
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• v.37 no.1
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• pp.40.2-40.2
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• 2012

Early-type dwarf galaxies are the most numerous galaxies in dense environments, making them ideal probes of the mechanisms that govern galaxy formation and evolution. Despite the common picture of an early-type dwarf galaxy as a quiescent one with no star formation and little gas, recent systematic investigations of early-type dwarf galaxies in the cluster revealed an unexpected variety among these apparently simple objects. In this talk, I review intriguing complexity of early-type dwarf galaxies in the cluster. I will also briefly introduce a new catalog of galaxies in the Virgo cluster using SDSS data, extended Virgo Cluster Catalog (EVCC).

• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.90.2-90.2
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• 2012

Galaxy merging plays a important role to the formation and evolution of galaxy. Early-type galaxies are believed to be formed by galaxy merging. We combined 3 color images in g,r,i band using Stripe82 image of which the surface brightness is 2 mag deeper than that of SDSS image. We classified early-type galaxies which have the merging features, the evidence of galaxy mergers through careful visual inspection. We investigated the IR properties of early-type galaxies with the merging feature using WISE data. We analyzed the star formation according to the type of galaxy. Early-type galaxies with the merging feature show the higher star formation than non-merging galaxies, but the difference is not significant. This results implies that quite a few early-type galaxies might be formed by dry merger, not wet merger. Meanwhile, the most of ULIRGs show tidal tail, on the other hand, early-type galaxies show tidal tail including shell structure. It suggests that ULIRGs have more gas and it might be in early stage of galaxy merging, early-type galaxies might be in the late stage of galaxy merging.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.2
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• pp.77.1-77.1
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• 2011

The sizes of galaxies are correlated with their masses or luminosities, which is known as the 'mass-size relation' or 'luminosity-size relation'. Those relations show scatters in the sense that the sizes of galaxies range somewhat widely at given mass or luminosity, which is largely affected by the morphologies or colors of the sample galaxies. However, the scatters of the relations are still large even when the galaxy sample is limited to red early-type galaxies: at fixed mass or luminosity, the largest red early-type galaxies are larger than the smallest red early-type galaxies by a factor of 4 - 5. This is a progress report of a study on what determines the sizes of red early-type galaxies. We investigate how the sizes of red early-type galaxies depend on several quantities of them, such as color, color gradient, axis ratio, local number density and mass-to-light ratio. The physical implication of those preliminary results is discussed.

• Journal of The Korean Astronomical Society
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• v.46 no.3
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• pp.141-149
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• 2013

We analyze the spiral structure of 1725 nearby spiral galaxies with redshift less than 0.02. We use the color images provided by the Sloan Digital Sky Survey. We determine the arm classes (grand design, multiple-arm, flocculent) and the broad Hubble types (early, intermediate, late) as well as the bar types (SA, SAB, SB) by visual inspection. We find that flocculent galaxies are mostly of late Hubble type while multiple-arm galaxies are likely to be of early Hubble type. The fractional distribution of grand design galaxies is nearly constant along the Hubble type. The dependence of arm class on bar type is not as strong as that of the Hubble type. However, there is about a three times larger fraction of grand design spirals in SB galaxies than in SA galaxies, with nearly constant fractions of multiple-arm galaxies. However, if we consider the Hubble type and bar type together, grand design spirals are more frequent in early types than in late types for SA and SAB galaxies, while they are almost constant along the Hubble type for SB galaxies. There are clear correlations between spiral structures and the local background density: strongly barred, early-type, grand design spirals favor high-density regions, while non-barred, late-type, flocculent galaxies are likely to be found in low-density regions.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.1
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• pp.76.2-76.2
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• 2019

Shells in early-type galaxies are low surface brightness tidal debris, which are wide concentric arcs of overdense stellar regions with large opening angles. The most widely accepted mechanism today for shell formation is the merger scenario, but the dominant merger type producing shells is not clearly understood yet: major/minor and wet/dry mergers. Since shells are regarded as smoking-gun evidence of merging events, detailed understanding of shell galaxies is very useful to constrain the formation process of early-type galaxies. In this study, we investigate the metallicity gradients of eight early-type shell galaxies using CALIFA IFU data to better understand the nature and origins of galaxy shells. We estimate simple stellar population properties out to three effective radius from the measurement of Lick/IDS absorption line indices. We compare the metallicity gradients of shell galaxies with those of normal early-type galaxies in the same mass range. In this presentation, we discuss how much the gradients of shell galaxies are different from those of normal early-type galaxies and what the existence of galaxy shells implies about galaxy formation.

• Journal of The Korean Astronomical Society
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• v.38 no.2
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• pp.145-148
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• 2005

We present a photometric study of galaxies in the central regions of six nearby galaxy clusters at redshift z=0.0231${\~}$0.0951. We have derived BVI photometry of the galaxies from the CCD images obtained at the Bohyunsan Optical Astronomical Observatory (BOAO) in Korea, and JHKs photometry of the bright galaxies from the 2MASS extended source catalog. Comparing the galaxy photometry results with the simple stellar population model of Bruzual & Charlot (2003) in the optical & NIR color-color diagrams, we have estimated the ages and metallicities of early type galaxies. We have found that the observed galaxies had recent star-formation mostly 5 ${\~}$ 7 Gyrs ago but the spread in age estimation is rather large. The average metallicities are [Fe/H]=0.l${\~}$0.5 dex. These results support the hypothesis that large early type galaxies in clusters are formed via hierarchical merging of smaller galaxies.

• The Bulletin of The Korean Astronomical Society
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• v.41 no.2
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• pp.34.2-34.2
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• 2016

We study the mid-infrared (MIR) properties of galaxies in compact groups and their environmental dependence using the Wide-field Infrared Survey Explorer data. We use a sample of 670 compact groups and their 2175 member galaxies with $M_r$ < -19 and 0.01 < z < 0.0741 from Sohn et al. (2016), which were identified through a friends-of-friends algorithm. We find that the MIR [3.4]-[12] colors of early-type galaxies in compact groups are on average bluer than those of early-type galaxies in clusters. Furthermore, we find that when compact groups have both early- and late-type member galaxies, the MIR colors of the late-type galaxies in those compact groups can be bluer than those of late-type galaxies in clusters. We also find that as background galaxy number densities of compact groups increase, compact group galaxies have higher early-type galaxy fractions and bluer MIR colors. These trends are also seen for background galaxies. However, at a given background density, compact group galaxies always have higher early-type galaxy fractions and bluer MIR colors than the background galaxies. Our findings suggest that the properties of compact group galaxies depend on both internal and external environments of the compact groups, and that galaxy evolution is faster in compact groups than in clusters.

• Journal of The Korean Astronomical Society
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• v.50 no.4
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• pp.111-124
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• 2017

The environmental dependence of the morphology of dwarf galaxies in isolated satellite systems is analyzed to understand the origin of the dwarf galaxy morphology using the visually classified morphological types of 5836 local galaxies with $z{\leq}0.01$. We consider six sub-types of dwarf galaxies, dS0, dE, $dE_{bc}$, dSph, $dE_{blue}$, and dI, of which the first four sub-types are considered as early-type and the last two as late-type. The environmental parameters we consider are the projected distance from the host galaxy ($r_p$), local and global background densities, and the host morphology. The spatial distributions of dwarf satellites of early-type galaxies are much different from those of dwarf satellites of late-type galaxies, suggesting the host morphology combined with $r_p$ plays a decisive role on the morphology of the dwarf satellite galaxies. The local and global background densities play no significant role on the morphology of dwarfs in the satellite systems hosted by early-type galaxies. However, in the satellite system hosted by late-type galaxies, the global background densities of dE and dSph satellites are significantly different from those of $dE_{bc}$, $dE_{blue}$, and dI satellites. The blue-cored dwarf satellites ($dE_{bc}$) of early-type galaxies are likely to be located at $r_p$ > 0.3 Mpc to keep their cold gas from the ram pressure stripping by the hot corona of early-type galaxies. The spatial distribution of $dE_{bc}$ satellites of early-type galaxies and their global background densities suggest that their cold gas is intergalactic material accreted before they fall into the satellite systems.

• Publications of The Korean Astronomical Society
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• v.7 no.1
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• pp.63-69
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• 1992

We have systematically investigated the X-ray spectra of normal galaxies, by using the Imaging Proportional Counter (IPC) data in the Einstein data base. We employed the X-ray color-color plot as well as the standard model fitting method which requires higher signal to noise ratio. We discuss X-ray emission mechanisms in terms of their spectral properties and the signature of cooling flows which are most likely present in X-ray bright early type galaxies. On the average, fits to absorbed thermal spectra show that the X-ray emission temperature of spirals is higher than that of ellipticals. This is consistent with our understanding that accreting binaries are a major X-ray source in spirals, while extended gaseous halos are present in ellipticals. The emission temperature becomes lower with increasing X-ray to optical luminosity ratio in E and S0 galaxies. This result is what we would expect if the emission of X-ray faint early type galaxies consists of a large evolved stellar component, while the gaseous emission becomes dominant in X-ray brighter galaxies. We also find a cool, self-absorbed core in some early type galaxies, which directly indicates the presence of cooling flows in such galaxies.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.2
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• pp.46.1-46.1
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• 2017

Late-type galaxies falling into a cluster would evolve being influenced by the interactions with both the cluster and the nearby cluster member galaxies. Most numerical studies, however, tend to focus on the effects of the former with little work done on those of the later. We thus perform numerical study on the evolution of a late-type galaxy falling radially toward the cluster center interacting with neighbouring early-type galaxies, using N-body, hydrodynamical simulations. Based on the information about the typical galaxy encounters obtained by using the galaxy catalog of Coma cluster, we run the simulations for the cases where a Milky Way Galaxy-like late-type galaxy, flying either edge-on or face-on, experiences six consecutive collisions with twice more massive early-type galaxies having hot gas in their halos. Our simulations show that the evolution of the late-type galaxy can be significantly affected by the high-speed multiple collisions with the early-type galaxies, such as on the cold gas content and the star formation activity, particularly through the hydrodynamic interactions between the cold disk and the hot gas halos. By comparing our simulation results with those of others, we claim that the role of the galaxy-galaxy interactions on the evolution of late-type galaxies in clusters could be comparable with that of the galaxy-cluster interactions, depending on the dynamical history.