• The Bulletin of The Korean Astronomical Society
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• v.37 no.2
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• pp.82.2-82.2
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• 2012

We present an investigation of X-ray hot gas halo in 21 early-type galaxies(ETGs) from cross-matched sample of XMM-Newton(2XMM-DR3 catalog) and SDSS DR 7(0.025 < z < 0.085 and Mr <-19.5). It has been controversial whether or not the environment affects X-ray luminosity of ETGs. In this research, we mainly considered how dense the surrounding galaxies of the target galaxy are and how isolated the target galaxy is from the nearest neighboring galaxy. It appears that the second environmental factor has more effects on X-ray luminosity (0.5-2 keV) of hot gas halo than the first one. We found that the closer a galaxy is to the nearest neighboring galaxy, the brighter it is when the galaxy is located within the neighbor galaxy's virial radius. However, when a galaxy is located outside the neighbor's virial radius, the luminosity does not show any trend. In this poster, we report preliminary results from our study.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.1
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• pp.44.4-45
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• 2015

We investigate the properties of galaxies belonging to the filaments in cosmic void regions, using the void catalogue constructed by Pan et al. (2012) from the SDSS DR7. To identify galaxy filaments within a void, voids with 30 or more galaxies are selected as a sample. We identify 3067 filaments in 1050 voids by applying the filament finding algorithm based on minimal spanning tree and reducing processes to spatial distribution of the void galaxies. We study the correlations between galaxy properties and the specific size of filament which quantifies the degree of the filament straightness. For example, the average magnitude and the magnitude of the faintest galaxy in filament decrease as the straightness of the filament increases. We also find that the correlations become stronger in rich filaments than in poor ones with fewer member galaxies. We discuss a physical explanation to our findings and their cosmological implications.

• The Bulletin of The Korean Astronomical Society
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• v.40 no.2
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• pp.32.2-32.2
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• 2015

Which mechanism governs star-formation activity in galaxies is still one of the most important, open questions in galactic astronomy. To address this issue, we investigate the specific star formation rate (sSFR) of late-type galaxies as functions of various structural parameters including the morphology, mass, radius, and mass compactness (MC). We use a sample of ~200,000 late-type galaxies with z = 0.02 ~ 0.2 from SDSS DR7 and a catalog of bulge-disk decomposition (Simard et al. 2011; Mendel et al. 2013). We find a remarkably strong correlation between bulge's MC and galaxy's sSFR, in the sense that galaxies with more compact bulge tend to be of lower sSFR. This seems counter-intuitive given that galactic sSFR is driven predominantly by disks rather than bulges and suggests that the central mass density plays a key role in recent star-forming activity. We discuss the physical cause of the new findings in terms of the bulge growth history and AGN activities.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.2
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• pp.66.1-66.1
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• 2014

We study the environment of the most massive galaxies and the most massive black holes. We use SDSS DR7 data, the catalog from Simard et al. (2011), Mendel et al. (2014), and KIAS value-added galaxy catalog (Choi et al. 2011). Currently, we investigate the number density as an environment around each galaxy. Number densities are measured by $5^{th}$ and $10^{th}$ nearest photometric galaxies within 7000km/s from the spectroscopic galaxies. The most massive galaxies (M > $10^{12}M_{\odot}$) or black holes ($M{\sim}10^{10}M_{\odot}$) tend to reside in very dense regions in comparison with less massive ones. We also present the research plan and future work.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.1
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• pp.37.1-37.1
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• 2012

We present mid-IR (MIR) and near-UV (NUV) properties of red sequence galaxies defined by optical color-magnitude relation. We use the Wide-field Infrared Survey Explorer (WISE) preliminary released data matched with the SDSS DR7/GALEX GR6. The red sequence galaxies with little emission lines show a wide spread of MIR (3.4um-12um) colors, implying a variety of MIR excess emission. We focus on the properties of the red sequence galaxies with MIR excess, comparing the properties of post-starburst galaxies to trace how galaxies migrate to the red sequence.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.1
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• pp.37.2-37.2
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• 2012

The A2199 supercluster at z=0.03 is one of the most massive system in nearby universe. In this supercluster, A2199 is kinematically connected to A2197 and several infalling galaxy groups. Thanks to a high-density environment and complex structures around A2199, this supercluster is an excellent laboratory for studying galaxy evolution. We determine the membership of galaxies in the supercluster using radial velocities of galaxies drawn from the SDSS spectroscopic DR7 data. We present an infrared view of this supercluster using AKARI and WISE data. We compare spatial distributions between early- and late-type galaxies, and also AGNs and star-forming galaxies. We also investigate how local and cluster-scale environments affect galaxy properties, such as IR-properties, star formation rates, and morphology transformations.

• The Bulletin of The Korean Astronomical Society
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• v.37 no.1
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• pp.49.2-49.2
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• 2012

We present an investigation of X-ray hot gas halo in 12 isolated early-type galaxies from cross-matched sample of XMM-Newton and SDSS DR 7(0.025 < z < 0.08588 and Mr <-19.5). Isolated galaxies that the separation between galaxy and the closest neighbor is farther than its virial radius are not affected by environments, and their X-ray hot gas halo can be studied without contribution of intragalactic medium in all circumstances. We find that isolated galaxies in low density have correlation of $L_X-L_R$ and those in high density have no trend. This suggests that internal process is much effective in low density and environmental effects play important role of this relationship in high density. We also find the galaxies affected by environments in the large scale structure. In this paper, we report preliminary results for the study.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.2
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• pp.29.2-29.2
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• 2010

We present elemental abundances of 412 blue compact dwarf galaxies (BCDs) at z=0.2~0.5 using the Sloan Digital Sky Survey (SDSS) DR7. The gas-phase nitrogen to oxygen abundance ratios (N/O) of sample galaxies increase as the oxygen to hydrogen abundance ratios (O/H) decrease. This indicates that the nitrogen is more enriched than the oxygen. We found that there is a noticeable distinction between the merger candidates and the isolated galaxies. Merging candidates show more enrichment of nitrogen abundance compared to isolated galaxies. On the other hand, neon and oxygen abundances for merging candidates are slightly lower than the isolated systems. We discuss the main cause of these trends with internal mixing and mass loss by fast rotation of young massive stars. We also discuss the environmental effect to the relation between specific star formation rate and galaxy mass.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.1
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• pp.58.1-58.1
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• 2011

We present elemental abundances of 95 blue compact dwarf galaxies (BCDs) at z=0.2~0.35 using the Sloan Digital Sky Survey (SDSS) DR7. We derived element abundances using Te method. We found that nitrogen abundance of merging BCDs are more enriched than normal BCDs by fast rotating young massive star. On the other hand, neon and oxygen abundances for merging BCDs are slightly lower than the normal BCDs. This might be result from the dilution by metal-poor gas infall during the interaction. This means that merging BCDs undergone star formation event for a long time than normal BCDs and we trying to explain using STARLIGHT code and various star formation rates (SFRs) ratios. At a result, merging BCDs have older stellar population (>10 Myr) more than normal BCDs and have clear distinction in elements abundances versus Ha/UV diagram. We also discuss the characteristics of post merger candidate using FUV to NUV ratios.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.2
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• pp.41.3-42
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• 2018

Redshift space distortion (RSD) is known as a powerful cosmological probe. The large-scale RSD has been detected by various redshift surveys and continues to be a major target of ongoing surveys. On the other hand, the small-scale RSD, called finger-of-god (FoG) effect, also has cosmological information, because different cosmological parameters cause different halo mass functions and viriarized velocities. We define the "length" of FoG and examine its dependence on cosmological parameters using the Multiverse simulation. We also use the SDSS DR7 data to see how strong constraints current data sets could provide. It is found that the volume-limited subsample D5, consisting of ~100,000 galaxies at z~0.08, yields $\Delta \Omega_m ~ 0.02$.