text: Yonsei Astronomy | Site / Paper
  Authors: Kim, Jenny J.; Lee, Young-Wook
  Publication: The Astrophysical Journal, Volume 869, Number 35, 2018 December
  Introduction (Kor): 구상성단의 화학적 진화에 대한 새로운 고찰
  Introduction (Eng):In order to investigate the origin of multiple stellar populations found in globular clusters (GCs) in the halo and bulge of the Milky Way, we have constructed chemical evolution models for their putative low-mass progenitors. In light of recent theoretical developments, we assume that supernova blast waves undergo blowout without expelling the pre-enriched ambient gas, while relatively slow winds of massive stars (WMSs), together with the winds and ejecta from low- to high-mass asymptotic giant branch stars, are all locally retained in these less massive systems. Interestingly, we find that the observed Na–O anti-correlations in metal-poor GCs can be reproduced when multiple episodes of starburst and enrichment are allowed to continue in these subsystems. A specific form of star formation history with decreasing time intervals between the successive stellar generations, however, is required to obtain this result, which is in good agreement with the parameters obtained from synthetic horizontal branch models. The "mass budget problem" is also much alleviated by our models without ad hoc assumptions on star formation efficiency, initial mass function, and the preferential loss of first-generation stars. We also apply these models to investigate the origin of super-He-rich red clump stars in the metal-rich bulge suggested by Lee et al. We find that chemical enrichment by the WMSs can naturally reproduce the required strong He enhancement in metal-rich subsystems. Our results further underscore that gas expulsion or retention is a key factor in understanding the multiple populations in GCs.
  Authors: Yoon, Mijin; Jee, M. James; Tyson, J. Anthony; Schmidt, Samuel; Wittman, David; Choi, Ami
  Publication: The Astrophysical Journal, Volume 870, Number 2, 2019 January 15
  Introduction (Kor): DLS 서베이를 활용한 우주론과 바리온 피드백 변수의 결정
  Introduction (Eng):We present cosmological parameter measurements from the Deep Lens Survey (DLS) using galaxy-mass and galaxy-galaxy power spectra in the multipole range ℓ=250∼2000. We measure galaxy-galaxy power spectra from two lens bins centered at z∼0.27 and 0.54 and galaxy-mass power spectra by cross-correlating the positions of galaxies in these two lens bins with galaxy shapes in two source bins centered at z∼0.64 and 1.1. We marginalize over a baryonic feedback process using a single-parameter representation and a sum of neutrino masses, as well as photometric redshift and shear calibration systematic uncertainties. For a flat ΛCDM cosmology, we determine S8=0.810+0.039−0.031, in good agreement with our previous DLS cosmic shear and the Planck Cosmic Microwave Background (CMB) measurements. Without the baryonic feedback marginalization, S8 decreases by ∼0.05 because the dark matter-only power spectrum lacks the suppression at the highest ℓ's due to Active Galactic Nuclei (AGN) feedback. Together with the Planck CMB measurement, we constrain the baryonic feedback parameter to Abaryon=1.07+0.31−0.39, which suggests an interesting possibility that the actual AGN feedback might be stronger than the recipe used in the OWLS simulations. The interpretation is limited by the validity of the baryonic feedback simulation and the one-parameter representation of the effect.
  Authors: Andrew K. Bradshaw, M. James Jee, J. Anthony Tyson
  Publication: Monthly Notices of the Royal Astronomical Society, 2019 January
  Introduction (Kor): 다중렌즈에 의해 발생하는 E/B 모드 현상연구
  Introduction (Eng): We explore the weak lensing E- and B-mode shear signals of a field of galaxy clusters using both large-scale structure N-body simulations and multicolour Suprime-cam & Hubble Space Telescope observations. Using the ray-traced and observed shears along with photometric redshift catalogues, we generate mass maps of the foreground overdensities by optimally filtering the tangential shear that they induce on background galaxies. We then develop and test a method to approximate the foreground structure as a superposition of Navarro-Frenk-White-like haloes by locating these overdensities and determining their mass and redshift, thereby modelling the background correlated shear field as a sum of lensings induced by the foreground clusters. We demonstrate that the B-mode maps and shear correlation functions, which are generated by similarly filtering the cross shear in this method, are in agreement with observations and are related to the estimated cluster masses and locations as well as the distribution of background sources. Using the foreground mass model, we identify several sources of weak lensing B modes including leakage and edge effects, source clustering, and multiple lensing which can be observed in deep cosmic shear surveys.
  Authors: Han, San; Smith, Rory; Choi, Hoseung; Cortese, Luca; Catinella, Barbara; Contini, Emanuele; Yi, Sukyoung K.
  Publication: The Astrophysical Journal, 2018 October
  Introduction (Kor): 은하단 확대 시뮬레이션 YZiCS를 이용한 암흑 헤일로의 전처리 및 질량 손실에 관한 연구
  Introduction (Eng): To understand the galaxy population in clusters today, we should also consider the impact of previous environments prior to cluster infall, namely preprocessing. We use the Yonsei Zoom-in Cluster Simulation, a hydrodynamic high-resolution zoom-in simulation of 15 clusters, and focus on the tidal stripping suffered by the dark matter halos of cluster members due to preprocessing. We find that ∼48% of today's cluster members were once satellites of other hosts. This is slightly higher than previous estimates, in part because we consider not just group-mass hosts but hosts of all masses. Thus, we find that the preprocessed fraction is poorly correlated with cluster mass and is instead related to each cluster's recent mass growth rate. Hosts less massive than groups are significant contributors, providing more than one-third of the total preprocessed fraction. We find that halo mass loss is a clear function of the time spent in hosts. However, two factors can increase the mass-loss rate considerably: the mass ratio of a satellite to its host and the cosmological epoch when the satellite was hosted. The latter means we may have previously underestimated the role of high-redshift groups. From a sample of heavily tidally stripped members in clusters today, nearly three-quarters were previously in a host. Thus, visibly disturbed cluster members are more likely to have experienced preprocessing. Being hosted before cluster infall enables cluster members to experience tidal stripping for extended durations compared to direct cluster infall and at earlier epochs when hosts were more destructive.
  Authors: Jung, Seoyoung L.; Choi, Hoseung; Wong, O. Ivy; Kimm, Taysun; Chung, Aeree; Yi, Sukyoung K.
  Introduction (Kor): 우주론적 유체 역학 시뮬레이션을 이용한 은하단 내 저 기체함량 은하의 기원 연구
  Introduction (Eng): The environmental effect is commonly used to explain the excess of gas-poor galaxies in galaxy clusters. Meanwhile, the presence of gas-poor galaxies at cluster outskirts, where galaxies have not spent enough time to feel the cluster environmental effect, hints at the presence of preprocessing. Using cosmological hydrodynamic simulations on 16 clusters, we investigate the mechanisms of gas depletion of galaxies found inside clusters. The gas-depletion mechanisms can be categorized into three channels based on where and when they took place. First, 34% of our galaxies are gas poor before entering clusters ("preprocessing"). They are mainly satellites that have undergone the environmental effect inside group halos. Second, 43% of the sample quickly became gas deficient in clusters before the first pericentric pass ("fast cluster processing"). Some of them were group satellites that are low in gas at the time of cluster entry compared to the galaxies directly coming from the field. Even the galaxies with large gas fractions take this channel if they fall into massive clusters (≳1014.5 M ⊙) or approach cluster centers through radial orbits. Third, 24% of our sample retain gas even after their first pericentric pass ("slow cluster processing") as they fall into the less massive clusters or have circular orbits. The relative importance of each channel varies with a cluster's mass, while the exact degree of significance is subject to large uncertainties. Group preprocessing accounts for one-third of the total gas depletion, but it also determines the gas fraction of galaxies at their cluster entry, which in turn determines whether a galaxy should take the fast or slow cluster processing.
  Authors: Young-Wook Lee, Seungsoo Hong, Dongwook Lim, Chul Chung, Sohee Jang, Jenny, J. Kim, and Seok-Joo Joo
  Publication: The Astrophysical Journal Letters, 862, L8, 2018 July
  Introduction (Kor): Double red clump 연구를 통한 우리은하 Bulge 형성 기원 연구
  Introduction (Eng): Two red clumps (RCs) observed in the color–magnitude diagram of the Milky Way bulge are widely accepted as evidence for an X-shaped structure that originated from the bar instability. A drastically different interpretation has been suggested, however, based on the He-enhanced multiple stellar population phenomenon as is observed in globular clusters (GCs). Because these two scenarios imply very different pictures of the formation of the bulge and elliptical galaxies, understanding the origin of the double RC is of crucial importance. Here we report our discovery that the stars in the two RCs show a significant (>5.3σ) difference in CN-band strength, in stark contrast to that expected in the X-shaped bulge scenario. The difference in CN abundance and the population ratio between the two RCs are comparable to those observed in GCs between the first- and later-generation stars. Because CN-strong stars trace a population with enhanced N, Na, and He abundances that originated in GCs, this is direct evidence that the double RC is due to the multiple population phenomenon, and that a significant population of stars in the Milky Way bulge were assembled from disrupted proto-GCs. Our result also calls for the major revision of the 3D structure of the Milky Way bulge, given that the current view is based on the previous interpretation of the double RC phenomenon.
  Authors : Jongwan Ko and M. James Jee
  Publication: Astrophysical Journal, 2018 August
  Introduction (Kor) : 가장 먼 은하단에서의 ICL 검출을 통해 그 기원을 연구
  Introduction (Eng) : Intracluster stars are believed to be unbound from their progenitor galaxies and diffused throughout the galaxy cluster, creating intracluster light (ICL). However, when and how these stars form are still in debate. To directly constrain the origin, one powerful method is to study clusters at the epoch when mature galaxy clusters began to appear. We report measurements of the spatial distribution, color, and quantity of diffuse intracluster stars for a massive galaxy cluster at a redshift of 1.24. This is the most distant galaxy cluster to date for which those three properties of the ICL have been quantified simultaneously. Our detection of the significant ICL fraction in this unprecedentedly high redshift regime strongly indicates that intracluster stars, contrary to most previous studies, might have formed during a short period and early in the history of the Virgo-like massive cluster formation and might be concurrent with the formation of the brightest cluster galaxy.
  Authors : Hoseung Choi, Sukyoung K. Yi, Yohan Dubois, Taysun Kimm, Julien. E. G. Devriendt, and Christophe Pichon
  Publication: Astrophysical Journal, 2018 April
  Introduction (Kor) : Horizon-AGN 시뮬레이션을 활용한 타원은하 회전의 환경 영향에 대한 연구
  Introduction (Eng) : The diversity in the ETG spin has drawn much attention for the last decade. We analyzed the Horizon-AGN simulation, a cosmological galaxy formation simulation of 100Mpc/h cube, to investigate the differences in the evolution of ETGs with different spin properties. We found that massive central ETGs form through numerous mergers and are preferentially very slowly rotating. However, group and cluster satellite ETGs, which are multiple times more numerous than the massive central ETGs, show slow rotation not because of mergers but because of environmental tidal interactions such as fly-bys or tidal force of the cluster potential. This differential evolutionary track may appear as distinct features in spin versus stellar mass plot, for example.
  Authors : Kyle Finner, M. James Jee, Nathan Golovich, David Wittman, William Dawson, Daniel Gruen, Anton M. Koekemoer, Brian C. Lemaux, and Stella Seitz
  Publication: Astrophysical Journal, 2017 December
  Introduction (Kor) : 허블 우주망원경과 수바루 망원경을 이용하여 하늘에서 두번째로 SZ 효과가 큰 PLCK G287.0+32.9 은하단의 암흑물질 연구
  Introduction (Eng) : The second most significant detection of the Planck Sunyaev−Zel'dovich survey, PLCK G287.0+32.9 (z = 0.385), boasts two similarly bright radio relics and a radio halo. A key missing puzzle for the merging scenario reconstruction is the underlying dark matter distribution in high resolution. We present a joint Subaru Telescope and Hubble Space Telescope weak-lensing analysis of the cluster. Our analysis shows that the mass distribution features four significant substructures.
  First Weak-lensing Results from "See Change": Quantifying Dark Matter in the Two z ≳ 1.5 High-redshift Galaxy Clusters SPT-CL J2040-4451 and IDCS J1426+3508
  Authors : Jee, M. James; Ko, Jongwan; Perlmutter, Saul; Gonzalez, Anthony; Brodwin, Mark; Linder, Eric; Eisenhardt, Peter
  Publication: Astrophysical Journal, 2017 October
  Introduction (Kor) : 허블 우주망원경을 이용한 고 적색편이 은하단의 암흑물질 함량 결정
  Introduction (Eng) : First use of the Wide Field Camera 3 (WFC3) on Hubble to quantify dark matter in two interesting high-z clusters
  Authors : Jongwon Park, Rory Smith, Sukyoung K. Yi
  Publication: Astrophysical Journal, 2017 August
  Introduction (Kor) : AGN FB 효과를 고려하면, 충돌하는 두 원반 은하의 별 생성률이 예상보다 적게 증가한다.
  Introduction (Eng) : Using numerical hydrodynamics simulations, we studied the effect of AGN feedback on the evolution of merging disk galaxies with various conditions.
  Authors : Jinsu Rhee, Rory Smith, Hoseung Choi, Sukyoung K. Yi, Yara Jaffe, Geame Candlish, and Ruben Sanchez-Janssen
  Publication: Astrophysical Journal, 2017 July
  Introduction (Kor) : 우주론적 유체역학 수치모사의 결과를 이용하여, 은하단에 병합한 은하들의 특징등을 위상공간분석을 통해 분석하는 논문입니다.
  Introduction (Eng) : Using cosmological hydrodynamic simulations, we provide phase-space diagrams as a tool for understanding cluster environmental effects which can be directly compared with real observations of galaxy clusters.