• 천문학회지
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• 제20권2호
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• pp.49-62
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• 1987

Using the detailed two-dimensional surface photometry of 39 galaxies, the observed profiles are decomposed into spheroid, disk and bar components simultaneously. From the analyses of decomposition parameters, the correlations among the three components are investigated to find the global property of barred galaxies. And the lens and ring components, and spiral arm patterns are also examined with Hubble type and decomposition parameters.

• 천문학회보
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• 제39권1호
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• pp.38.2-38.2
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• 2014

Radial light profiles of bars are known to be related to the morphology of their host galaxies in a way that bars in early type disk galaxies show flat radial light profile, while bars in late type disk galaxies show exponential profile. To quantify how flat or steep bar profiles are, we have performed detailed two-dimensional decompositions on 3.6 micron images for 144 barred galaxies from the Spitzer Survey of Stellar Structure in Galaxies (S4G), and then modeled bar profiles with Sersic functions. We find that bars in classical bulge, higher bulge-to-total (B/T) galaxies are flatter than bars in bulgeless, lower B/T galaxies. In particular, we find that the presence of a bulge almost always guarantees that the bar is flat. Conversely, bulgeless galaxies, mostly have bars with steep profiles. This implies that the light profile of bars may be a dynamical age indicator of bars. We also find that the shape of bars are boxy and do not change with B/T. This indicates that as galaxies evolve, bars change their light profile while keeping their outermost shape boxy.

• 천문학회보
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• 제38권2호
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• pp.37.2-37.2
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• 2013

Recently it turns out that simple-looking elliptical galaxies and lenticular galaxies are more complex and intriguing than expected. One of the most surprising and intriguing findings in extragalactic studies during the last two decades is a discovery that color distribution of the globular clusters in these galaxies is bimodal, suggesting that there are two subpopulations: blue and red globular clusters. We present a determination of the two-dimensional shape parameters of the blue and red globular cluster systems (GCSs) in a large number of bright elliptical galaxies and lenticular galaxies. The position angles of both and red GCSs show a correlation with those of the stellar light distribution, showing that the major axes of the GCSs are well aligned with those of their host galaxies. However, the shapes of the red GCSs show a tight correlation with the stellar light distribution as with the rotation property of their host galaxies, while the shapes of the blue GCSs do much less. These provide clear geometric evidence that the origins of the blue and red globular clusters are distinct and that these galaxies may have dual halos: a blue (metal-poor) halo and a red (metal-rich) halo. These two halos show significant differences in metallicity, structure, and kinematics, indicating that they are formed in two distinguishable ways. The red halos might have formed via dissipational processes with rotation, while the blue halos are through accretion.

• 천문학회지
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• 제47권1호
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• pp.1-13
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• 2014

We analyze the dependence of disk morphology (arm class, Hubble type, bar type) of nearby spiral galaxies on the galaxy environment by using local background density (${\Sigma}_n$), projected distance ($r_p$), and tidal index (T I) as measures of the environment. There is a strong dependence of arm class and Hubble type on the galaxy environment, while the bar type exhibits a weak dependence with a high frequency of SB galaxies in high density regions. Grand design fractions and early-type fractions increase with increasing ${\Sigma}_n$, $1/r_p$, and T I, while fractions of flocculent spirals and late-type spirals decrease. Multiple-arm and intermediate-type spirals exhibit nearly constant fractions with weak trends similar to grand design and early-type spirals. While bar types show only a marginal dependence on ${\Sigma}_n$, they show a fairly clear dependence on $r_p$ with a high frequency of SB galaxies at small $r_p$. The arm class also exhibits a stronger correlation with $r_p$ than ${\Sigma}_n$ and T I, whereas the Hubble type exhibits similar correlations with ${\Sigma}_n$ and $r_p$. This suggests that the arm class is mostly affected by the nearest neighbor while the Hubble type is affected by the local densities contributed by neighboring galaxies as well as the nearest neighbor.

• 천문학논총
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• 제30권2호
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• pp.503-505
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• 2015

The galaxy cluster is an important object for investigating the large scale structure and evolution of galaxies. Recent wide and deep near-IR surveys provide an opportunity to search for galaxy clusters in the high redshift universe. We have identified candidate clusters of 0.8< z <1.2 from the $25deg^2$ SA22 field using an optical-near-IR dataset from merged UKIDSS DXS, IMS and CFHTLS catalogs. Using these candidates, we investigate the star forming activity of member galaxies. Consequently, at z ~1, the star forming activity of cluster galaxies is not distinguishable from those of field galaxies, which is different from members in local clusters. This means the environmental effect becomes more important for $M_{\ast}>10^{10}M_{\odot}$ galaxies at z <1.

• 천문학회보
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• 제37권2호
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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.

• 천문학회지
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• 제26권1호
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• pp.13-32
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• 1993

We have conducted BVI photographic surface photometry of four spiral galaxies NGC1087, NGC2715, NGC2844 and NGC3593, by making use of the Kiso Schmidt plates. Detailed examination of the morphological properties of the galaxies using isophotal maps and luminosity profiles showed that all the program galaxies have some peculiarities in their luminosity distributions. NGC1087 and NGC2715 have extremely small nuclei with inner rings which contain several bright HII regions. NGC2844 has a very large bulge whose luminosity dominates over the disk luminosity in all the radii. The I-band luminosity profile of NGC3593 shows shallower gradient than B- and V-band profiles. We were able to successfully decompose the luminosity profile into a bulge following de Vaucouleurs $\gamma^{1/4}-law$ and an exponential disk only for NGC 3953. Other galaxies have more complicated luminosit profiles.

• 천문학회보
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• 제41권1호
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• pp.67.3-68
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• 2016

We present evidence of the bar driven secular evolution on disks from z~0.8 to z~0.01. Using $3.6{\mu}m$ images of nearby galaxies from the Spitzer Survey of Stellar Structure in Galaxies (S4G) and images from the Cosmological Evolution Survey (COSMOS), we find that barred galaxies show a light deficit in the disk surrounding the bar within the bar radius. We quantify this light deficit and find that galaxies with a stronger bar (longer, higher Bar/T) show a more pronounced light deficit. We examine snapshots from N-body simulations and confirm that as a barred galaxy evolves, the bar becomes longer and the light deficit becomes more pronounced. Theoretical studies have predicted that bars evolve by capturing nearby disk stars and employing them to make the bar more elongated and stronger. Therefore the light deficit in the disk is likely produced by bars, and thus bars play a major role in shaping their host galaxies, redistributing not only the gaseous but also the stellar mass within galaxies, with important consequences to their subsequent evolution.

• 천문학회보
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• 제43권2호
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• pp.35.3-36
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• 2018

One of the most prevalent knowledge about disk galaxies, which dominate the population of the local Universe, is that they consist of stellar structures with different kinematics, such as thin disk, bulge, and halo. Therefore, investigating when and how these components develop in a galaxy is the key to understanding the evolution of galaxies. Using the NewHorizon simulation, we can resolve the detailed structures of galaxies, in the field environment, from the early Universe where star formation and mergers were most active. We first decompose stellar particles in a galaxy into a disk and a dispersion-dominated, spheroidal, component based on their orbits and then see how these components evolve in terms of mass and structure. At high redshift z~3, galaxies are mostly dispersion-dominated as stars are formed misaligned with the galactic rotational axis. At z=1~2, massive galaxies start to dominantly form disk stars, while less massive galaxies do much later. Furthermore, massive galaxies are forming thinner and larger disks with time, and the preexistent disks are heated or even disrupted to become a part of dispersion-dominated component. Thus, the mass growth of spheroidal components at later epochs is dominated by disrupted stars with disk origins and accreted stars at large radii.

• 천문학회보
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• 제38권2호
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• pp.53.2-53.2
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• 2013

외부 고리를 갖는 은하들(Outer ring galaxies)을 SDSS dr7 목록에서 분류하여, 이들이 갖는 특징과 링 구조(Ring structure)를 형성하는데 외부환경의 요인이 있는지 조사하고자 했다. z<0.05, b/a>0.6, R>6"의 조건에서 25,308개의 은하들을 추출하였고, SDSS image tool을 이용하여 531개의 외부 고리 은하(Outer ring galaxies)또는 외부고리를 갖고 있는 것처럼 보이는 은하(Ring-like galaxies)를 육안으로 분류하였다. 5개(u, g, r, i, z)의 필터로 관측되어진 CCD 이미지의 분석으로 최종적으로 69개의 외부고리 은하(Outer ring galaxies)를 선정하였다. 통계적으로 전체 은하에서 외부 고리 은하가 차지하는 비율이 약 0.2726%라는 결과를 얻게 되었고, 은하들의 주변의 환경을 조사한 결과 배경밀도와 비리얼 반경에 있어서 다른 형태의 고리를 갖고 있는 은하들과의 유의미한 특이점은 보이지 않았다.