• 천문학회보
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• 제38권2호
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• pp.45.2-45.2
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• 2013

We studied recent evolution of M31 and M33 with star-forming regions and hot massive stars. We use GALEX far-UV and near-UV imaging to detect the star-forming regions and trace the recent star formation across the entire disk of galaxies. The GALEX imaging, combining deep sensitivity and entire coverage of these galaxies, provides a complete picture of the recent star formation in M31 and M33, and its variation with environment throughout these galaxies. We also show results from recent extensive surveys in M31 and M33 with Hubble Space Telescope multi-wavelength data including UV filters, which imaged several regions at a linear resolution of less than half a pc in these galaxies. Both datasets allow us to study the hierarchical structure of star formation: the youngest stellar groups are the most compact, and are often arranged withing broader, sparser structures. The derived recent star-formation rates are rather similar for the two galaxies, when scaled for the respective areas.

• 천문학회보
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• 제37권1호
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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.

• 천문학회보
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• 제37권1호
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• pp.34.2-34.2
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• 2012

In the context of structure formation in a hierarchical Universe, the relevance of mergers to radio-loud active galaxies is still under debate. I employ two different observational approaches to investigate the merger history of active galaxies, using several different samples of radio-loud AGN. I will first show results from the investigation of a complete sample of flat-spectrum radio-AGN and their role in a merger-driven evolution of galaxies. In the second part of my talk I will focus on the investigation of the close environment of radio-loud active galaxies, using data from the new VISTA-VIDEO near-infrared survey. Strong evidence is found supporting a close connection between merger events and radio-loud AGN.

• 천문학회지
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• 제37권4호
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• pp.205-210
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• 2004

The interaction of disk galaxies with intergalactic winds has been invoked as a possible mechanism of the generation of galactic warps. Here we discuss conditions under which intergalactic flows can be relevant for warping field galaxies. Constraints include the heating of the outer disk, the level of asymmetry in the vertical distribution of the volume gas density, the angular frequency of the warp, the symmetry of galactic warps amplitude between the approaching and receding sides of the galaxy, and the speed of the intergalactic flow whether subsonic or supersonic. These constraints are discussed in this paper in reference to the proposal of Lopez-Corredoira et al. that warps can be a natural consequence of accretion flows onto the disk.

• 천문학회보
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• 제45권1호
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• pp.29.3-29.3
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• 2020

Cosmology is a study to understand the origin, fundamental property, and evolution of the universe. Nowadays, many observational data of galaxies have become available, and one needs large-volume numerical simulations with good quality of the spatial distribution for a fair comparison with observation data. On the other hand, since galaxies' evolution is affected by both gravitational and baryonic effects, it is nontrivial to populate galaxies only by N-body simulations. However, full hydrodynamic simulations with large volume are computationally costly. Therefore, alternative galaxy assignment methods to N-body simulations are necessary for successful cosmological studies. In this talk, I would like to introduce the MBP-galaxy abundance matching. This novel galaxy assignment method agrees with the spatial distribution of observed galaxies between 0.1Mpc ~ 100Mpc scales. I also would like to introduce mock galaxy catalogs of the Horizon Run 4 and Multiverse simulations, large-volume cosmological N-body simulations done by the Korean community. Finally, I would like to introduce some recent works with those mock galaxies used to understand our universe better.

• Journal of Astronomy and Space Sciences
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• 제34권3호
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• pp.183-197
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• 2017

We present simulations of the optical-band images of high-redshift galaxies utilizing 845 near-ultraviolet (NUV) images of nearby galaxies obtained through the Galaxy Evolution Explorer (GALEX). We compute the concentration (C), asymmetry (A), Gini (G), and $M_{20}$ parameters of the GALEX NUV/Sloan Digital Sky Survey r-band images at z ~ 0 and their artificially redshifted optical images at z = 0.9 and 1.6 in order to quantify the morphology of galaxies at local and high redshifts. The morphological properties of nearby galaxies in the NUV are presented using a combination of morphological parameters, in which early-type galaxies are well separated from late-type galaxies in the $G-M_{20}$, $C-M_{20}$, A-C, and $A-M_{20}$ planes. Based on the distribution of galaxies in the A-C and $G-M_{20}$ planes, we examine the morphological K-correction (i.e., cosmological distance effect and bandshift effect). The cosmological distance effect on the quantitative morphological parameters is found to be significant for early-type galaxies, while late-type galaxies are more greatly affected by the bandshift effect. Knowledge of the morphological K-correction will set the foundation for forthcoming studies on understanding the quantitative assessment of galaxy evolution.

• 천문학회지
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• 제43권6호
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• pp.191-200
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• 2010

We present the Korea Institute for Advanced Study Value-Added Galaxy Catalog (KIAS VAGC), a catalog of galaxies based on the Large Scale Structure (LSS) sample of New York University Value-Added Galaxy Catalog (NYU VAGC) Data Release 7. Our catalog supplements redshifts of 10,497 galaxies with 10 < $r_P\;{\leq}\;17.6$ (1455 with 10 < $r_P\;{\leq}\;14.5$) to the NYU VAGC LSS sample. Redshifts from various existing catalogs such as the Updated Zwicky Catalog, the IRAS Point Source Catalog Redshift Survey, the Third Reference Catalogue of Bright Galaxies, and the Two Degree Field Galaxy Redshift Survey have been put into the NYU VAGC photometric catalog. Our supplementation significantly improves spectroscopic completeness: the area covered by the spectroscopic sample with completeness higher than 95% increases from 2.119 to 1.737 sr. Our catalog also provides morphological types of all galaxies that are determined by the automated morphology classification scheme of Park & Choi (2005), and related parameters, together with fundamental photometry parameters supplied by the NYU VAGC. Our catalog contains matches to objects in the Max Planck for Astronomy (MPA) & Johns Hopkins University (JHU) spectrum measurements (Data Release 7). This new catalog, the KIAS VAGC, is complementary to the NYU VAGC and MPA-JHU catalog.

• 천문학회지
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• 제34권2호
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• pp.59-66
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• 2001

In this paper, we investigate the correlation between the radial ultraviolet color distribution and the shapes of the ultraviolet isophote for elliptical galaxies (M32, NGC 1399) and spiral bulges (of M31, M81) by using their archival UIT images. For M31, M81, and NGC 1399, the radial ultraviolet color distributions show a two-component trend; as the distance from the galactic center increase the color becomes redder in the inner region while it becomes bluer in the outer region. On the other hand, the color of M32 continues to become bluer with the increasing galactocentric distance. We also find, unlike the optical/IR images, significant variations of the position angle and the ellipticity in the ultraviolet isophotes of M31, M81, and NGC 1399 through the inner regions. For M32, the variation is significant in the outer region. Since these variation implies the triaxiality of their intrinsic shapes, we suggest that the early-type galaxies and spiral bulges with a radial color gradient in ultraviolet tend to have a triaxiality. On the other hand, the shape parameter characterized by the fourth order cosine Fourier coefficient of the isophote, a(4)/a, indicates that the systematic deviations of the ultraviolet isophotes of the four galaxies are smaller than $\~0.2\%$ in units of the semi-major axis. The latter result implies that the ultraviolet isophotes of the galaxies have a pure elliptical shape rather than the boxy or disky shapes. Therefore, there is no clear evidence of correlation between the radial ultra-violet color gradient and the boxy/disky shapes of isophotes.

• 천문학회보
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• 제44권1호
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• pp.78.1-78.1
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• 2019

Using a method to correct redshift space distortion (RSD) for individual galaxies, we mapped the real space distributions of galaxies in the Sloan Digital Sky Survey (SDSS) Data Release 7(DR7). We use an ensemble of mock catalogs to demonstrate the reliability of this extension, showing that it allows for an accurate recovery of the real-space correlation functions and galaxy biases. We also demonstrate that, using an iterative method applied to intermediate scale clustering data, we can obtain an unbiased estimate of the growth rate of structure $f\sigma_8$, which is related to the clustering amplitude of matter, to an accuracy of $\sim 10\%$. Applying this method to the Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7), we construct a real-space galaxy catalog spanning the redshift range $0.01 \leq z \leq 0.2$, which contains 584,473 galaxies in the North Galactic Cap (NGC). Using this data we, infer $0.376 \pm 0.038$ at a median redshift z=0.1, which is consistent with the WMAP9 cosmology at $1\sigma$ level. By combining this measurement with the real-space clustering of galaxies and with galaxy-galaxy weak lensing measurements for the same sets of galaxies, we are able to break the degeneracy between $f$, $\sigma_8$ and $b$. From the SDSS DR7 data alone, we obtain the following cosmological constraints at redshift $z=0.1$ for galaxies.

• 천문학회지
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• 제15권1호
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• pp.41-48
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• 1982

PDS was used to get the structure of two barred spiral galaxies NGC 1313 and NGC 1365. The result shows that NGC 1365 has both a deep spheroidal component and an exponential disk, but NGC 1313 has only an prominent exponential component. The luminosity profiles indicate that KGC 1313 is in type I and NGC 1365 belongs to type II. The length scales $({\alpha}^{-1})$ were derived from the exponential luminosity distributions as 1.64 kpc for NGC 1313 and 2.49kpc for KGC 1365.