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The astrophysics and cosmology group consists of prof. Changbom Park, research profs. Juhan Kim and Ho Seong Hwang, and eight research fellows. In 2014 Prof. Park is carrying out the Korea Dark Energy Survey (KDES) project, which aims to uncover the nature of the dark energy component of the universe. Prof. Park led the Korean Scientist Group (KSG) participating in the Sloan Digital Sky Survey (SDSS) III that ended in June 2014. KIAS joined the succeeding survey SDSS-IV that started in July 2014 and consists of three survey programs, APOGEE-2, MaNGA, and eBOSS. At the end of 2014 KIAS joined the Mid-Scale Dark Energy Spectroscopic Instrument (DESI), which plans to construct a new wide-field multi-object spectrograph and operate it on the Mayall telescope at Kitt Peak in Arizona in the 2018-2022 time frame for dark energy-related sciences. Prof. Park works as the director of the KIAS Center for Advanced Computation. He also works for the KIAS trans-disciplinary research program as the Chair of the Planning and Steering Committees. He is working as the Editor-in-Chief of Journal of the Korean Astronomical Society. He is leading a group of astronomers, the Survey Science Group, which holds meetings to study and plan the future major astronomical survey projects. Individual members of the astrophysics group have been active in his/her research in 2014. Research Prof. Juhan Kim and Prof. Park analyzed large cosmological simulation data of Horizon Run 4 (HR4) that was run on the Tachyon-II cluster of KISTI supercomputing center. A huge set of halo merging trees was built and extensively used to test the standard LCDM cosmological model against various observations. Research Prof. Ho Seong Hwang joined the astrophysics group in September 2014. He works on comparison of the galaxy distribution from dense redshift surveys with the matter distribution from weak-lensing analysis of galaxy clusters. He is using wide-field galaxy redshift surveys such as HectoMAP to study the properties of observed large-scale structures (LSS) in comparison with those from the Horizon Runs. Dr. Jeong-Sun Hwang and Prof. Park are making a series of numerical simulations of interacting galaxies that have hot gas halos in the initial galaxy models. They studied the distance encounters of early- and late-type galaxies, focusing on the effects of the hot halo gas and the intracluster medium on galaxy properties. Dr. Hwang moved to Kyung-Hee university. Dr. L'Huillier, Profs. C. Park and J. Kim are studying the rates and types of halo interactions as a function of the small- and large-scale environments and their redshift evolution using HR4. They are also studying LSS using cosmological simulations to constrain the growth factor of cosmic structures. Dr. Seokcheon Lee worked on the standard perturbation theory (SPT) and the Lagrangian theory to improve them for the exact solutions without using the de Sitter approximation. Using SPT he investigates the difference in quasi-linear matter power spectra among the models that have the same CMB temperature power spectrum. He is also studying the methods of measuring the bias factor from observations. Dr. Sungwook E. Hong is studying the optimal algorithm for the target allocation of the robotic fiber positioning system and the metrology system of TAIPAN, a project of Australian Astronomical Observatory. With Profs. C. Park and J. Kim, he applied the one-to-one correspondency galaxy assignment scheme to HR4, and studied the properties of mock galaxies such as velocity dispersion of galaxy groups with those of SDSS galaxy sample. Together with Prof. C. Park, Dr. Xiao-Dong Li is applying the Alcock-Pacyznski test to the large-scale density gradient field and the cosmic skeleton constructed from galaxy distributions. He made many tests using the HR3 mock survey data. He also worked on constraining the holographic dark energy model, and a work probing the possible high order evolution in dark energy equation of state. Dr. Hyunmi Song is studying the large-scale environment of SDSS DR7 quasars using the latest SDSS DR12 Baryon Oscillation Spectroscopic Survey CMASS galaxies. The properties of quasars are inspected as a function of the background galaxy density. Dr. Bernardo Cervantes Sodi is studying the frequency of barred galaxies as a function of environment. With prof. Cheng Li in Shanghai, he found a significant trend for early-type galaxies with a bar to be more strongly clustered on scales from a few 100 kpc to 1 Mpc when compared to unbarred early-type galaxies. This indicates that the presence of a bar in early-type galaxies depends on the location within their host dark matter halos. Raphael Gobat joined the astrophysics group in September 2014. His main scientific interests are distant galaxy clusters and galaxy evolution at high redshifts. During this last four months his work has been a continuation of his recent studies on environmental signatures in the properties of satellites of z~2 galaxies. Dr. Fadia Salmi also joined the astrophysics group in September 2014. She is working with Ho Seong Hwang and collaborators to estimate the sizes of a large number of galaxies at intermediate redshifts. The goal is to study the relation between sizes and stellar masses at intermediate redshifts and to quantify the number of compact galaxies. Publication
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