나. 연. 소 : 나의 연구를 소개합니다
YAM 회원들이 게재한 논문을 소개하고 직접 논문의 포인트를 설명하는 코너입니다. 많은 관심과 citation(?) 을 부탁드립니다 :^).
1. 강이정 (연세대학교)
제목 : Early-type Host Galaxies of Type Ia Supernovae. I. Evidence for Downsizing
저자 : Kang, Yijung; Kim, Young-Lo; Lim, Dongwook; Chung, Chul; Lee, Young-Wook
Abstract
Type Ia supernova (SN Ia) cosmology provides the most direct evidence for the presence of dark energy. This result is based on the assumption that the lookback time evolution of SN Ia luminosity, after light curve corrections, would be negligible. Recent studies show, however, that the Hubble residual (HR) of SN Ia is correlated with the mass and morphology of host galaxies, implying the possible dependence of SN Ia luminosity on host galaxy properties. In order to investigate this more directly, we have initiated a spectroscopic survey for early-type host galaxies, for which population age and metallicity can be more reliably determined from the absorption lines. In this first paper of the series, we present here the results from high signal-to-noise ratio (≳100 per pixel) spectra for 27 nearby host galaxies in the southern hemisphere. For the first time in host galaxy studies, we find a significant (∼3.9σ) correlation between host galaxy mass (velocity dispersion) and population age, which is consistent with the “downsizing” trend among non-host early-type galaxies. This result is rather insensitive to the choice of population synthesis models. Since we find no correlation with metallicity, our result suggests that stellar population age is mainly responsible for the relation between host mass and HR. If confirmed, this would imply that the luminosity evolution plays a major role in the systematic uncertainties of SN Ia cosmology.
Link
http://adsabs.harvard.edu/abs/2016ApJS..223....7K
저자 : Kang, Yijung; Kim, Young-Lo; Lim, Dongwook; Chung, Chul; Lee, Young-Wook
Abstract
Type Ia supernova (SN Ia) cosmology provides the most direct evidence for the presence of dark energy. This result is based on the assumption that the lookback time evolution of SN Ia luminosity, after light curve corrections, would be negligible. Recent studies show, however, that the Hubble residual (HR) of SN Ia is correlated with the mass and morphology of host galaxies, implying the possible dependence of SN Ia luminosity on host galaxy properties. In order to investigate this more directly, we have initiated a spectroscopic survey for early-type host galaxies, for which population age and metallicity can be more reliably determined from the absorption lines. In this first paper of the series, we present here the results from high signal-to-noise ratio (≳100 per pixel) spectra for 27 nearby host galaxies in the southern hemisphere. For the first time in host galaxy studies, we find a significant (∼3.9σ) correlation between host galaxy mass (velocity dispersion) and population age, which is consistent with the “downsizing” trend among non-host early-type galaxies. This result is rather insensitive to the choice of population synthesis models. Since we find no correlation with metallicity, our result suggests that stellar population age is mainly responsible for the relation between host mass and HR. If confirmed, this would imply that the luminosity evolution plays a major role in the systematic uncertainties of SN Ia cosmology.
Link
http://adsabs.harvard.edu/abs/2016ApJS..223....7K
Ia형 초신성(Type Ia Supernovae)의 밝기가 모은하의 특성, 특히 질량과 상관 관계를 갖는다는 기존 연구들에 의한 결과가 어떤 물리적인 원인으로 비롯한 것인지 알아내기 위한 연구를 수행하였다. 이를 위해 이들의 조기형 모은하 (Early-type Host galaxies)의 긴 슬릿 분광 관측을 통해 수소 흡수선 및 중원소 흡수선의 세기를 측정하여 이들의 나이와 중원소 함량을 결정하였다. 이로부터 나이가 많은 조기형 모은하일 수록 더 무거운 질량을 갖는다는 상관 관계를 확인하였다.
2. 이광호 (서울대학교)
제목 : Dependence of Barred Galaxy Fraction on Galaxy Properties and Environment
저자 : Lee, Gwang-Ho; Park, Changbom; Lee, Myung Gyoon; Choi, Yun-Young
Abstract
We investigate the dependence of the occurrence of bars in galaxies on galaxy properties and environment. We use a volume-limited sample of 33,391 galaxies brighter than Mr = -19.5 + 5logh at 0.02 <= z <= 0.05489, drawn from the Sloan Digital Sky Survey Data Release 7. We classify the galaxies into early and late types, and identify bars by visual inspection. Among 10,674 late-type galaxies with axis ratio b/a > 0.60, we find 3240 barred galaxies (f bar = 30.4%) which divide into 2542 strong bars (f SB1 = 23.8%) and 698 weak bars (f SB2 = 6.5%). We find that f SB1 increases as u - r color becomes redder and that it has a maximum value at intermediate velocity dispersion (σ sime150 km s-1). This trend suggests that strong bars are dominantly hosted by intermediate-mass systems. Weak bars prefer bluer galaxies with lower mass and lower concentration. In the case of strong bars, their dependence on the concentration index appears only for massive galaxies with σ > 150 km s-1. We also find that f bar does not directly depend on the large-scale background density when other physical parameters (u - r color or σ) are fixed. We discover that f SB1decreases as the separation to the nearest neighbor galaxy becomes smaller than 0.1 times the virial radius of the neighbor regardless of neighbor's morphology. These results imply that strong bars are likely to be destroyed during strong tidal interactions and that the mechanism for this phenomenon is gravitational and not hydrodynamical. The fraction of weak bars has no correlation with environmental parameters. We do not find any direct evidence for environmental stimulation of bar formation.
Link
http://adsabs.harvard.edu/abs/2012ApJ...745..125L
저자 : Lee, Gwang-Ho; Park, Changbom; Lee, Myung Gyoon; Choi, Yun-Young
Abstract
We investigate the dependence of the occurrence of bars in galaxies on galaxy properties and environment. We use a volume-limited sample of 33,391 galaxies brighter than Mr = -19.5 + 5logh at 0.02 <= z <= 0.05489, drawn from the Sloan Digital Sky Survey Data Release 7. We classify the galaxies into early and late types, and identify bars by visual inspection. Among 10,674 late-type galaxies with axis ratio b/a > 0.60, we find 3240 barred galaxies (f bar = 30.4%) which divide into 2542 strong bars (f SB1 = 23.8%) and 698 weak bars (f SB2 = 6.5%). We find that f SB1 increases as u - r color becomes redder and that it has a maximum value at intermediate velocity dispersion (σ sime150 km s-1). This trend suggests that strong bars are dominantly hosted by intermediate-mass systems. Weak bars prefer bluer galaxies with lower mass and lower concentration. In the case of strong bars, their dependence on the concentration index appears only for massive galaxies with σ > 150 km s-1. We also find that f bar does not directly depend on the large-scale background density when other physical parameters (u - r color or σ) are fixed. We discover that f SB1decreases as the separation to the nearest neighbor galaxy becomes smaller than 0.1 times the virial radius of the neighbor regardless of neighbor's morphology. These results imply that strong bars are likely to be destroyed during strong tidal interactions and that the mechanism for this phenomenon is gravitational and not hydrodynamical. The fraction of weak bars has no correlation with environmental parameters. We do not find any direct evidence for environmental stimulation of bar formation.
Link
http://adsabs.harvard.edu/abs/2012ApJ...745..125L
이 연구는 은하의 막대 구조가 어떠한 은하의 내외부 환경 조건에서 존재할 수 있는지에 대해 조사한 것이다. 은하의 막대 비율은 red하거나 중간 정도의 질량을 가진 은하에서 높게 나타남을 발견하였으며, 은하의 주변 밀도와 막대 비율은 뚜렷한 상관 관계를 보이지 않았다. 그러나 이웃한 은하와 매우 가깝게 상호작용을 할 경우, 막대비율은 많이 감소한다. 이는 은하의 강한 상호작용이 막대 구조를 와해시킴을 의미한다.
3. 이광호 (서울대학교)
제목 : Do Bars Trigger Activity in Galactic Nuclei?
저자 : Lee, Gwang-Ho; Woo, Jong-Hak; Lee, Myung Gyoon; Hwang, Ho Seong; Lee, Jong Chul; Sohn, Jubee; Lee, Jong Hwan
Abstract
We investigate the connection between the presence of bars and active galactic nucleus (AGN) activity, using a volume-limited sample of ~9000 late-type galaxies with axis ratio b/a > 0.6 and Mr < -19.5 + 5 log h at low redshift (0.02 <= z <~ 0.055), selected from Sloan Digital Sky Survey Data Release 7. We find that the bar fraction in AGN-host galaxies (42.6%) is ~2.5 times higher than in non-AGN galaxies (15.6%), and that the AGN fraction is a factor of two higher in strong-barred galaxies (34.5%) than in non-barred galaxies (15.0%). However, these trends are simply caused by the fact that AGN-host galaxies are on average more massive and redder than non-AGN galaxies because the fraction of strong-barred galaxies (f SB) increases with u - r color and stellar velocity dispersion. When u - r color and velocity dispersion (or stellar mass) are fixed, both the excess of f SB in AGN-host galaxies and the enhanced AGN fraction in strong-barred galaxies disappears. Among AGN-host galaxies we find no strong difference of the Eddington ratio distributions between barred and non-barred systems. These results indicate that AGN activity is not dominated by the presence of bars, and that AGN power is not enhanced by bars. In conclusion, we do not find clear evidence that bars trigger AGN activity.
Link
http://adsabs.harvard.edu/abs/2012ApJ...750..141L
저자 : Lee, Gwang-Ho; Woo, Jong-Hak; Lee, Myung Gyoon; Hwang, Ho Seong; Lee, Jong Chul; Sohn, Jubee; Lee, Jong Hwan
Abstract
We investigate the connection between the presence of bars and active galactic nucleus (AGN) activity, using a volume-limited sample of ~9000 late-type galaxies with axis ratio b/a > 0.6 and Mr < -19.5 + 5 log h at low redshift (0.02 <= z <~ 0.055), selected from Sloan Digital Sky Survey Data Release 7. We find that the bar fraction in AGN-host galaxies (42.6%) is ~2.5 times higher than in non-AGN galaxies (15.6%), and that the AGN fraction is a factor of two higher in strong-barred galaxies (34.5%) than in non-barred galaxies (15.0%). However, these trends are simply caused by the fact that AGN-host galaxies are on average more massive and redder than non-AGN galaxies because the fraction of strong-barred galaxies (f SB) increases with u - r color and stellar velocity dispersion. When u - r color and velocity dispersion (or stellar mass) are fixed, both the excess of f SB in AGN-host galaxies and the enhanced AGN fraction in strong-barred galaxies disappears. Among AGN-host galaxies we find no strong difference of the Eddington ratio distributions between barred and non-barred systems. These results indicate that AGN activity is not dominated by the presence of bars, and that AGN power is not enhanced by bars. In conclusion, we do not find clear evidence that bars trigger AGN activity.
Link
http://adsabs.harvard.edu/abs/2012ApJ...750..141L
이 연구는 막대나선은하의 막대 구조와 은하핵의 활동성 유무의 관계에 대해 살펴본 것으로, 다양한 은하 특성 파라미터 상에서 막대의 비율과 AGN 비율 간의 관계를 조사하였다. 결과적으로 우리는 AGN 활동과 막대의 유무 사이에는 뚜렷한 관계가 없음을 확인하였다.
4. 이광호 (서울대학교)
제목 : Galaxy Evolution in the Mid-infrared Green Valley: A Case of the A2199 Supercluster
저자 : Lee, Gwang-Ho; Hwang, Ho Seong; Lee, Myung Gyoon; Ko, Jongwan; Sohn, Jubee; Shim, Hyunjin; Diaferio, Antonaldo
Abstract
We study the mid-infrared (MIR) properties of the galaxies in the A2199 supercluster at z = 0.03 to understand the star formation activity of galaxy groups and clusters in the supercluster environment. Using the Wide-field Infrared Survey Explorer data, we find no dependence of mass-normalized integrated star formation rates of galaxy groups/clusters on their virial masses. We classify the supercluster galaxies into three classes in the MIR color-luminosity diagram: MIR blue cloud (massive, quiescent, and mostly early-type), MIR star-forming sequence (mostly late-type), and MIR green valley galaxies. These MIR green valley galaxies are distinguishable from the optical green valley galaxies in the sense that they belong to the optical red sequence. We find that the fraction of each MIR class does not depend on the virial mass of each group/cluster. We compare the cumulative distributions of surface galaxy number density and cluster/group-centric distance for the three MIR classes. MIR green valley galaxies show the distribution between MIR blue cloud and MIR star-forming (SF) sequence galaxies. However, if we fix galaxy morphology, early- and late-type MIR green valley galaxies show different distributions. Our results suggest a possible evolutionary scenario of these galaxies: (1) late-type MIR SF sequence galaxies → (2) late-type MIR green valley galaxies → (3) early-type MIR green valley galaxies → (4) early-type MIR blue cloud galaxies. In this sequence, the star formation of galaxies is quenched before the galaxies enter the MIR green valley, and then morphological transformation occurs in the MIR green valley.
Link
http://adsabs.harvard.edu/abs/2015ApJ...800...80L
저자 : Lee, Gwang-Ho; Hwang, Ho Seong; Lee, Myung Gyoon; Ko, Jongwan; Sohn, Jubee; Shim, Hyunjin; Diaferio, Antonaldo
Abstract
We study the mid-infrared (MIR) properties of the galaxies in the A2199 supercluster at z = 0.03 to understand the star formation activity of galaxy groups and clusters in the supercluster environment. Using the Wide-field Infrared Survey Explorer data, we find no dependence of mass-normalized integrated star formation rates of galaxy groups/clusters on their virial masses. We classify the supercluster galaxies into three classes in the MIR color-luminosity diagram: MIR blue cloud (massive, quiescent, and mostly early-type), MIR star-forming sequence (mostly late-type), and MIR green valley galaxies. These MIR green valley galaxies are distinguishable from the optical green valley galaxies in the sense that they belong to the optical red sequence. We find that the fraction of each MIR class does not depend on the virial mass of each group/cluster. We compare the cumulative distributions of surface galaxy number density and cluster/group-centric distance for the three MIR classes. MIR green valley galaxies show the distribution between MIR blue cloud and MIR star-forming (SF) sequence galaxies. However, if we fix galaxy morphology, early- and late-type MIR green valley galaxies show different distributions. Our results suggest a possible evolutionary scenario of these galaxies: (1) late-type MIR SF sequence galaxies → (2) late-type MIR green valley galaxies → (3) early-type MIR green valley galaxies → (4) early-type MIR blue cloud galaxies. In this sequence, the star formation of galaxies is quenched before the galaxies enter the MIR green valley, and then morphological transformation occurs in the MIR green valley.
Link
http://adsabs.harvard.edu/abs/2015ApJ...800...80L
이 연구는 가까운 초은하단 A2199 은하 구성원들의 중적외선 특성과 환경 효과에 대한 것이다. WISE 중적외선 자료를 이용하여 은하들의 중적외선 광도-색지수 분포를 살펴보았으며, 이 분포도에서 "mid-infrared green valley"를 정의하였다. 우리는 mid-infrared green valley에서 일어나는 은하 진화의 특성과 환경이 미치는 영향을 조사하였다.
5. 장석준 (세종대학교)
제목 : Formation of Raman Scattering Wings around H alpha, H beta, and Pa alpha in Active Galactic
저자 : Chang, Seok-Jun; Heo, Jeong-Eun; Di Mille, Francesco; Angeloni, Rodolfo; Palma, Tali; Lee, Hee-Won
Abstract
Powered by a supermassive black hole with an accretion disk, the spectra of active galactic nuclei (AGNs) are characterized by prominent emission lines including Balmer lines. The unification schemes of AGNs require the existence of a thick molecular torus that may hide the broad emission line region from the view of observers near the equatorial direction. In this configuration, one may expect that the far-UV radiation from the central engine can be Raman scattered by neutral hydrogen to reappear around Balmer and Paschen emission lines, which can be identified with broad wings. We produce Hα, Hβ, and Paα wings using a Monte Carlo technique to investigate their properties. The neutral scattering region is assumed to be a cylindrical torus specified by the inner and outer radii and the height. While the covering factor of the scattering region affects the overall strengths of the wings, the wing widths are primarily dependent on the neutral hydrogen column density {N}{{H} {{I}}} being roughly proportional to {N}{{H} {{I}}}1/2. In particular, with {N}{{H} {{I}}}={10}23 {{cm}}-2 the Hα wings typically show a width ∼ 2× {10}4 {km} {{{s}}}-1. We also find that Hα and Paα wing profiles are asymmetric with the red part stronger than the blue part and an opposite behavior is seen for Hβ wings.
Link
http://adsabs.harvard.edu/abs/2015ApJ...814...98C
저자 : Chang, Seok-Jun; Heo, Jeong-Eun; Di Mille, Francesco; Angeloni, Rodolfo; Palma, Tali; Lee, Hee-Won
Abstract
Powered by a supermassive black hole with an accretion disk, the spectra of active galactic nuclei (AGNs) are characterized by prominent emission lines including Balmer lines. The unification schemes of AGNs require the existence of a thick molecular torus that may hide the broad emission line region from the view of observers near the equatorial direction. In this configuration, one may expect that the far-UV radiation from the central engine can be Raman scattered by neutral hydrogen to reappear around Balmer and Paschen emission lines, which can be identified with broad wings. We produce Hα, Hβ, and Paα wings using a Monte Carlo technique to investigate their properties. The neutral scattering region is assumed to be a cylindrical torus specified by the inner and outer radii and the height. While the covering factor of the scattering region affects the overall strengths of the wings, the wing widths are primarily dependent on the neutral hydrogen column density {N}{{H} {{I}}} being roughly proportional to {N}{{H} {{I}}}1/2. In particular, with {N}{{H} {{I}}}={10}23 {{cm}}-2 the Hα wings typically show a width ∼ 2× {10}4 {km} {{{s}}}-1. We also find that Hα and Paα wing profiles are asymmetric with the red part stronger than the blue part and an opposite behavior is seen for Hβ wings.
Link
http://adsabs.harvard.edu/abs/2015ApJ...814...98C
AGN 통합 모형에서 토러스 모양의 중성수소지역을 가정하였다. 그리고 거대질량 블랙홀에서 나오는 라이먼 계열 근처의 자외선 광자를 산란지역으로 입사시켜 라만 산란되어 나오는 H alpha, H beta 그리고 Pa alpha 광자들의 스펙트럼을 시뮬레이션을 통해 얻어 내고 분석하였다.