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The astrophysics and cosmology group of Korea Institute for Advanced Study consists of prof. Changbom Park, research prof. Juhan Kim, and nine research fellows. In 2013 Prof. Park started a new science project called Korea Dark Energy Survey (KDES), which is aiming to develop theories of dark energy measurement and to uncover the nature of the dark energy component of the universe. Prof. Park is leading the Korean Scientist Group participating in the Sloan Digital Sky Survey (SDSS) III that will continue through June 2014. In 2013 KIAS signed the MOU with by the Astrophysical Research Consortium to join the upcoming new survey, SDSS-IV. The survey will start in July 2014 and consists of three survey programs, the APO Galactic Evolution Experiment 2 (APOGEE-2), the Mapping Nearby Galaxies at APO (MaNGA) survey, and the Extended Baryon Oscillation Spectroscopic Survey (eBOSS). Prof. Park is the Lead Scientist of the Korean Scientists Group, which consists of three KIAS research fellows and members in the Korea Astronomy and Space Science Institute (one senior scientist, a postdoc, and unlimited number of students). Prof. Park works as the director of the KIAS computer center, Center for Advanced Computation (KIAS CAC). He also works for the KIAS trans-disciplinary research program that started in 2012. He is working as the Editor-in-Chief of Journal of the Korean Astronomical Society. He created and is leading a group of astronomers, the Survey Science Group, who gather together to study and plan the future major astronomical survey projects. Individual members of the astrophysics and cosmology group have been active in his/her research in 2013. Prof. Park and Research Prof. Juhan Kim are working on simulation of the HectoMAP survey that is being carried out by Margaret Geller's group at Harvard-Smithsonian Center for Astrophysics. Prof. Kim is making a new medium resolution large cosmological simulation called Horizon Run 4 on the Tachyon-II cluster of KISTI supercomputer center. Prof. Park and Kim, together with Prof. Yun-Young Choi at Kyung Hee University, also studied the topology of Luminous Red Galaxies from the Sloan Digital Sky Survey Data Release 7 to constrain cosmology and non-Gaussianity in the primordial density fluctuations. Dr. Jeong-Sun Hwang and Prof. Park have worked on distant interactions between early- and late-type galaxies using N-body/hydrodynamic simulations. Varying the orbital parameters of the interactions, they analyzed the amplitude of the star burst and total mass of stars formed due to the encounters in excess of those of the isolated cases. In particular, the effects of hot gas surrounding a more massive early-type galaxy on the star formation activity of a late-type galaxy through hydrodynamic interactions are carefully examined. Dr. Benjamin L'Huillier, together with Prof. Park and Prof. Juhan Kim, has studied the effects of the initial conditions on the statistics of the large-scale structures of the Universe in cosmological N-body simulations. Importance of carefully choosing the order of perturbation theory, starting redshift, glass/grid pre-initial configuration, and N-body code are thoroughly examined. Dr. L'Huillier and Prof. Park are also studying the galaxy interaction type and rate as a function of the large-scale environment and its redshift evolution using a series of N-body simulations. Dr. Seokcheon Lee has worked on the method of using the growth of structure for constraining the matter density and Hubble expansion rate. This work is published at Journal of Cosmology and Astroparticle Physics on Feb. 2014. He is also working on the Eulerian (Lagrangian) perturbation theories to forecast the signal in baryon acoustic oscillation. These works improve the current approximate calculations for the dark energy models. This will show the correct dark energy dependence of observables. He published a paper titled as "Optimal strategies : theoretical approaches to the parameterization of the dark energy equation of state" at Astrophysics and Space Science on Jan. 2014. Dr. Cristiano Sabiu has been working on cosmological constraints from the geometrical distortions in the large scale structure of galaxies, using the Alcock-Paczynski test. In collaboration with Maayane Soumagnac (UCL, London), he has been analyzing the SDSS Baryon Oscillation Spectroscopic Survey in search of baryonic effects in the cross-correlation between the galaxy luminosity and number density fields. In in work with Prof. Bruce Bassett (UCT, Cape Town) has put observational constraints on possible deviations from the standard redshift-distance relations, which may result from exotic models of gravity. Dr. Sungwook E. Hong, a KDES research fellow, has participated in the development of TAIPAN, a precursor of a spectroscopy instrument for the Giant Magellan Telescope (GMT) made by Australian Astronomical Observatory. He has developed the automatic system for the measurement of focal-ratio degradation (FRD) of optical fiber and tested FRD of various fiber types and configurations used in TAIPAN. He has also studied the optimal algorithm for the identification and target selection of Starbugs, the robotic fiber positioning system of TAIPAN and GMT. Dr. Xiao-Dong Li joined KIAS as a KDES research fellow in March 2013. Together with Prof. Park, he is working on a project applying the Alcock-Pacyznski test to the large scale structure by using the gradient field and the orientation of the cosmic skeleton constructed from galaxy distribution. He tested the ideas on the Horizon Run 3 mock survey data, and is planning to applying these methods to the BOSS galaxy and quasar data. Together with his Chinese collaborators, he also finished a work constraining the holographic dark energy model from the Planck data combined with low redshift data, and a work probing the possible high order evolution in dark energy equation of state by using the most recent BAO, CMB, and supernovae data. Dr. Hyunmi Song, a new KDES research fellow, and Prof. Park are trying to find the connection between quasars and their host dark matter halos. Quasars are rare and very bright objects that enable us to explore the early universe. Their connection with the underlying matter density field is very poorly known. Using the quasar catalog from the Sloan Digital Sky Survey Data Release 7 they have identified the quasar groups and made a statistical analyses. A quantitative comparison with cosmological simulations will be made with the better knowledge on the quasar phenomenon. Dr. Annie Hou has been focusing on the nature of green galaxies, which show intermediate properties between the two (more dominant) populations of red and blue galaxies. Using the KIAS_VAGC of the SDSS galaxies, she has looked at the correlations between various properties, such as star formation rate, signs of merger activity and stellar mass, to investigate the possible underlying physical processes that result in observed properties of these galaxies which appear to be in a 'transitional' state. Additionally, she has worked on finishing a last paper from her PhD thesis, which involves looking at the role of pre-processing in SDSS groups and clusters. Dr. Bernardo Cervantes Sodi joined the KIAS Astrophysics group in October 2013. His fields of interest are galaxy structure, evolution and morphology, focusing specially on the spin parameter of disc galaxies. More recently, using carefully selected samples from the Sloan Digital Sky Survey, he is studying internal properties of galaxies that might influence the likelihood of galaxies hosting bars, finding that low spinning galaxies poor in gas present a higher occurrence of hosting strong bars, when compared with high spinning, gas rich galaxies. Another important property that seems relevant on establishing the likelihood of galaxies hosting bars is the ration between mass in stars and the mass in the dark matter halo, showing that the more dark matter dominated galaxies are more stable against bar instabilities. Prof. Park is collaborating with Prof. A. N. Ramaprakash at The Inter-University Centre for Astronomy and Astrophysics (IUCAA) in India on making a survey of interacting galaxy systems and large-scale distribution of galaxies. For this purpose he participated in developing a spectrometer and camera system employing fiber-based IFUs, called Devasthal Optical Telescope Integral Field Spectrograph (hereafter DOTIFS) to be used on the upcoming 3.6m Devasthal telescope. For this purpose Mr. Haeun Chung of Seoul National University, a research assistant of KIAS, was sent to IUCAA to participate in development of the DOTIFS. He will also carry out the survey of interacting galaxies when the system is completed. Publication
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