• 천문학회보
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• 제41권1호
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• pp.69.2-69.2
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• 2016

We study the environmental dependence of the mass-size relation for the most massive early type galaxies (M>$10^{10.7}M_{\odot}$) in the redshift range 0.10~0.15. The sizes of galaxies are measured by non-parametric method. We find that galaxies more massive than $10^{11.1}M_{\odot}$ show the environmental dependence in the mass-size relation. The galaxies with M>$10^{11.1}M_{\odot}$ located in the densest, cluster like environment have larger sizes and extended surface brightness profiles than their counterparts located in a low dense environment. We also find that the environmental dependence of the mass-size relation is more significant for the brightest cluster galaxies (BCGs) than non-BCGs. We use the semi analytic galaxy formation simulation based on the Millennium 1 Simulation for interpretation. Our result can be explained with a hierarchical growth of the most massive galaxies through dissipation-less merger in dense environment.

• 천문학회보
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• 제38권1호
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• pp.37.1-37.1
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• 2013

We present a result of a statistical studies on nuclear activities of compact group galaxies. It is suggested that the galaxy interaction can trigger the nuclear activity by producing the gas inflow to the center of galaxies. To understand the connection between galaxy interaction and nuclear activity, we study the fraction of Active Galactic Nuclei (AGN) host galaxies in compact groups, known as the most favored environment for galaxy interaction. We select 59 spectroscopically confirmed compact groups in the SDSS DR6. Using the emission line ratio, we determine the spectral types of compact group galaxies and obtain the fraction of AGN-host galaxies. We compare this fraction with those in other galaxy environments. For the early type galaxies, we find that the AGN fraction of compact group galaxies are lower than field galaxies, but higher than cluster galaxies. On the other hand, the AGN fraction of compact group galaxies is similar to those for field and cluster environment for the late type galaxies. Implications of this result will be discussed.

• 천문학회보
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• 제36권1호
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• pp.58.2-58.2
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• 2011

Park, Gott, & Choi (2008) found that when a galaxy is located within the virial radius from its closest neighbor and the neighbor is an elliptical, the probability of the galaxy to be an elliptical is very sensitive to the large-scale background density over a few Mpc scales. They suggested that the large-scale dependence can be arise if the temperature of a diffuse hot gas held by elliptical galaxies are higher in higher density environment. In this study, to understand the large-scale environment affects the X-ray properties of individual galaxies, we investigated the dependence of the X-ray luminosities of the elliptical galaxies on the large-scale environment using X-ray and optical data which we selected from the ROSAT All-Sky Survey and the Sloan Digital Sky Survey Data Release 7. To exclude galaxies embedded in an intra-group/cluster medium which could enhance their observed X-ray luminosity, we used isolated elliptical galaxies.

• 천문학논총
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• 제25권3호
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• pp.65-69
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• 2010

Observations of large samples of galaxies from low to high redshifts are composing a picture of remarkable simplicity: (1) The star formation rate (SFR) of starforming galaxies scales almost linearly with mass, strongly decline with cosmic time, and exhibits very small scatter around the average relation. (2) Due to the high observed SFRs the mass of galaxies at high redshifts must increase very rapidly, and yet the mass function of star forming galaxies evolves only very slightly with redshift. (3) At all redshifts the fraction of quenched (passively evolving) galaxies increases with galactic stellar mass and with local overdensity, with the remarkable property that the relative efficiency of "mass quenching" is independent of environment, and that of "environment quenching" is independent of mass. In a recent paper by the zCOSMOS collaboration, Peng et al. (2010) demonstrate that these three empirical facts suffice to account for the observed evolution of the galaxy mass function and naturally generate the "double-Schechter" mass function for quenched galaxies.

• 한국지구과학회지
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• 제41권3호
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• pp.211-221
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• 2020

이 연구는 SDSS DR7의 적색이동(z)<0.05이고, 동시에 R_pet>6 arcsec, 단축과 장축의 비(b/a)>0.6인 외부은하 25,308개를 분류하고, 색 영상을 육안으로 조사하여 고리 모양의 구조를 가진 531개 은하를 선별했다. 이 은하들이 일차적 표본으로 사용되었고, 이 중 90개의 외부고리 은하 후보를 선택했다. 후보 은하의 u, g, r, i, z 영상에 대한 표면 측광으로부터 도출한 특성을 조사하여 최종으로 69개의 외부고리 은하를 결정했다. 외부고리 은하는 국부은하의 0.3%를 차지하는 것으로 나타났으며, 두 개의 환경 인자, 즉, 가장 가까운 은하까지의 투영 거리와 국부 배경 은하 밀도를 이용하여, 외부고리 은하의 환경 특성을 조사했다. 외부고리 은하의 환경이 다른 은하의 경우와 비교하여 눈에 띄는 차이의 결과는 보이지 않았다.

• 천문학논총
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• 제30권2호
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• pp.491-494
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• 2015

We present 12CO (2-1) data for four spiral galaxies (NGC 4330, NGC 4402, NGC 4522, NGC 4569) in the Virgo cluster that are undergoing different ram pressure stages. The goal is to probe the detailed molecular gas properties under strong intra-cluster medium (ICM) pressure using high-resolution millimeter data taken with the Submillimeter Array (SMA). Combining this with Institut de RadioAstronomie $Millim{\acute{e}}trique$ (IRAM) data, we also study spatially resolved temperature and density distributions of the molecular gas. Comparing with multi-wavelength data (optical, $H\small{I}$, UV, $H{\alpha}$), we discuss how molecular gas properties and star formation activity change when a galaxy experiences $H\small{I}$ stripping. This study suggests that ICM pressure can modify the physical and chemical properties of the molecular gas significantly even if stripping does not take place. We discuss how this affects the star formation rate and galaxy evolution in the cluster environment.

• 천문학회보
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• 제45권1호
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• pp.64.1-64.1
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• 2020

Galaxy groups are the place where many galaxies feel the impact of the surroundings (e.g., merging, tidal interaction, ram pressure stripping) before joining bigger structures like (sub)clusters. A significant fraction of galaxies is quenched in the group environment. Such "pre-processing" of galaxies in groups is likely to affect galaxy evolution tremendously. To better understand how environmental processes in galaxy groups affect molecular gas, star formation activity, and galaxy evolution, we carried out CO imaging observations of group galaxies, using the Atacama Compact Array (ALMA/ACA). We selected all the targets that have been detected in the GEMS-HI survey for two groups, making the sample of 40 galaxies (18 galaxies in IC 1459 group and 22 galaxies in NGC 4636 group). Our ALMA/ACA observation is the first CO imaging survey for two groups. In this work, we present CO images of group galaxies, together with their star formation maps and HI images. Our ACA CO data show the asymmetric distribution of molecular gas in some of our samples. We discuss the impact of the group environment on molecular gas and star formation activity.

• 천문학회보
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• 제39권2호
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• pp.55.2-55.2
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• 2014

Role of environments is one of today's most widely discussed and debated topic in the field of extra-galactic astronomy. Extreme morphology-density relations found in low-mass galaxies are considered to be the result of an effective role played by environment in the evolution of these galaxies. I will present the results from our dedicated study of early-type dwarf galaxies (dEs) in different environments using imaging and spectroscopic data. We find that Virgo cluster dEs have a variety of structural and kinematic properties. A significant fraction of dEs possesses disk features, such as spiral arm and bar, while a central nucleus seems to be universal in these low mass galaxies. We also find that a majority of dEs are fast rotator and their rotation curves are much steeper than that of spiral galaxies of similar mass. Finally I will discuss how the different environmental mechanisms, i.e., gas-stripping or tidal interaction, can contribute to form heterogeneous dEs in Virgo cluster.

• 천문학회보
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• 제37권2호
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• pp.88.1-88.1
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• 2012

We utilize Sloan Digital Sky Survey DR7 spectroscopic data of ~340 star forming galaxies in the Virgo cluster to investigate their chemical properties depending on the environments. The chemical evolution of galaxies is linked to their star formation histories (SFHs), as well as to the gas interchange in different environments. In this sense, galaxy metallicity could be an observable parameter providing information on the impact of the environment on the galaxy SFH and/or the galaxy gas content. Thus, we derived gaseous metallicity (e.g., oxygen abundance) of star forming galaxies located in different regions of the Virgo cluster using well-known empirical calibrations. We also estimated their star formation rate (SFR) using H alpha luminosity. Inorder to investigate the chemical properties of these galaxies, we examined relations between various parameters: metallicity vs. luminosity, SFR vs. luminosity, and metallicity vs. cluster-centric radius. From our results, we discuss environmental effects of cluster to the chemical properties of star forming galaxies.

• 천문학회지
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• 제49권6호
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• pp.239-253
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• 2016

We determined the warp parameters of 192 warped galaxies which are selected from 340 edge-on galaxies using color images as well as r-band isophotal maps. We derive the local background density (${\Sigma}_n$) to examine the dependence of the warp amplitudes on the galaxy environment. We find a clear trend that strongly warped galaxies are likely to be found in high density regions where tidal interactions are supposed to be frequent. However, the correlation between ${\alpha}_{\omega}$ and ${\Sigma}_n$ is too weak for weakly warped galaxies (${\alpha}_{\omega}$ < $4^{\circ}$) and the cumulative distributions of weakly warped galaxies are not significantly different from those of galaxies with no detectable warps. This suggests that tidal interactions do not play a decisive role in the formation of weak warps.