• Journal of The Korean Astronomical Society
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• v.44 no.5
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• pp.161-175
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• 2011

We examine the dependence of the morphology of spiral galaxies on the environment using the KIAS Value Added Galaxy Catalog (VAGC) which is derived from the Sloan Digital Sky Survey (SDSS) DR7. Our goal is to understand whether the local environment or global conditions dominate in determining the morphology of spiral galaxies. For the analysis, we conduct a morphological classification of galaxies in 20 X-ray selected Abell clusters up to z~0.06, using SDSS color images and the X-ray data from the Northern ROSAT All-Sky (NORAS) catalog. We analyze the distribution of arm classes along the clustercentric radius as well as that of Hubble types. To segregate the effect of local environment from the global environment, we compare the morphological distribution of galaxies in two X-lay luminosity groups, the low-$L_x$ clusters ($L_x$ < $0.15{\times}10^{44}$erg/s) and high-$L_x$ clusters ($L_x$ > $1.8{\times}10^{44}$erg/s). We find that the morphology-clustercentric relation prevails in the cluster environment although there is a brake near the cluster virial radius. The grand design arms comprise about 40% of the cluster spiral galaxies with a weak morphology-clustercentric radius relation for the arm classes, in the sense that flocculent galaxies tend to increase outward, regardless of the X-ray luminosity. From the cumulative radial distribution of cluster galaxies, we found that the low-$L_x$ clusters are fully virialized while the high-$L_x$ clusters are not.

• The Bulletin of The Korean Astronomical Society
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• v.43 no.1
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• pp.33.2-34
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• 2018

Galaxies associated with massive groups/clusters are normally gas deficient in contrast to field galaxies. HI observations on such galaxies have revealed signs of violent gas stripping, the direct evidence of the environmental effect. At the same time, the notable number of passive galaxies at the cluster outskirts indicates the presence of pre-processing that makes galaxies gas-poor before entering clusters. We investigate the possible channels for the production of the gas deficient galaxies using the state-of-the-art cosmological hydrodynamic zoom-in simulations of 16 clusters (Choi&Yi). We find cluster effect and pre-processing together play an important role in producing the gas-poor galaxies and in both cases gas loss qualitatively agrees with the ram pressure stripping description. Among the currently gas-poor cluster galaxies, 34% are pre-processed before the cluster infall. They are mainly satellites that have undergone ram pressure stripping in group halos. 43% deplete quickly after arriving at cluster during their first approach to the center. Some of them are group halo satellites low in the gas at the infall compared to galaxies directly coming from the field. 24% retain gas even after their first pericentric pass mainly because they are falling into low mass clusters and/or they have a circular orbit that minimizes the ram pressure effect. This study highlights the importance of the past history of galaxies, especially in group halos, before joining the current cluster when understanding the excess of passive galaxies in clusters.

• The Bulletin of The Korean Astronomical Society
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• v.39 no.1
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• pp.39.1-39.1
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• 2014

We present the results of our analysis of the RR Lyrae (RRL) variable stars detected in two transition-type dwarf galaxies (dTrans), ESO294-G010 and ESO410-G005 in the Sculptor group, which is known to be one of the closest neighboring galaxy groups to our Local Group. Using deep archival images from the Advanced Camera for Surveys (ACS) onboard the Hubble Space Telescope (HST), we have identified a sample of RR Lyrae candidates in both dTrans galaxies [219 RRab (RR0) and 13 RRc (RR1) variables in ESO294-G010; 225 RRab and 44 RRc stars in ESO410-G005]. The metallicities of the individual RRab stars are calculated via the period-amplitude-[Fe/H] relation derived by Alcock et al. This yields mean metallicities of <[Fe/H]>_{ESO294} = -1.77 +/- 0.03 and <[Fe/H]>_{ESO410} = -1.64+/- 0.03. The RRL metallicity distribution functions (MDFs) are investigated further via simple chemical evolution models; these reveal the relics of the early chemical enrichment processes for these two dTrans galaxies. In the case of both galaxies, the shapes of the RRL MDFs are well-described by pre-enrichment models. This suggests two possible channels for the early chemical evolution for these Sculptor group dTrans galaxies: 1) The ancient stellar populations of our target dwarf galaxies might have formed from the star forming gas which was already enriched through "prompt initial enrichment" or an "initial nucleosynthetic spike" from the very first massive stars, or 2) this pre-enrichment state might have been achieved by the end products from more evolved systems of their nearest neighbor, NGC 55.

• Journal of the Korean earth science society
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• v.25 no.5
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• pp.336-347
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• 2004

This study investigated the effects of the application of a variety of ICTs cause the effects on self-directed learning capability, creativity and problem-solving ability. In order to achieve the above aim, Web-Based Instructions(WBI) and instructions using CD-ROM Titles for the unit of 'the solar system and the galaxy' were applicated and analyzed which belongs to the area of 'the earth' in the subject 'science' for high school students. Instructions using WBI materials and CD-ROM titles were found to be effective on 'self-conception', 'creativity', 'future inclination', 'self-assessment ability', 'openness' and' initiative' improvement all of which belong to self-directed learning characteristics. They did not, however, show meaningful effect on improving 'learning eagemess' and 'responsibility' improvement. On looking into self-directed learning characteristics according to prerequisite learning levels, both groups and these for instruction using CD-ROM learning materials were found to have no effect on interaction. With respect to problem-solving ability improvement which is characteristic of the instruction using ICTs, WBI proved more fruitful than instruction using CD-ROM titles on improving scholastic achievement level. WBI was effective on 'fluency', 'originality' and 'resistance to premature closure'. It on the other hand, was of no use on 'abstraction of titles' and 'elaborateness' These results came from the following characteristics: WBI came into effect on 'fluency' and 'originality' in the areas of variety and vitality, which are characteristic of WBI. In the area of resistance to premature closure WBI was effective on organizing learning contents owing to the animation of picture materials which are variously presented in the web site. As a result of WBI questionnaire about WBI, an excellent effect on the structure of display, quantity of information, indication and instruction, supplementary study and further study were discussed.