2015.1 ~ 2015.12

The Astrophysics and Cosmology group is headed by Prof. Changbom Park and Research Profs. Juhan Kim and Ho Seong Hwang. There are nine research fellows: Dr. Bejamin L’Huillier, Dr. Seokcheon Lee, Dr. Sungwook Hong, Dr. Xiao-Dong Li, Dr. Hyunmi Song, Dr. Raphael Gobat, Dr. Fadia Salmi, Dr. Stephen Appleby, and Dr. Jihye Shin.

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 is leading the Korean Scientist Group (KSG) participating in the Sloan Digital Sky Survey (SDSS) IV that started in July 2014. SDSS IV consists of three survey programs, APOGEE-2, MaNGA, and eBOSS. He is also a member of 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 worked as the director of the KIAS Center for Advanced Computation. He also worked 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 2015. Research Prof. Juhan Kim investigated, with prof. Park, the cosmological nonlinear density evolution by analyzing the density fluctuations and phase-phase correlations of density modes observed in cosmological simulations. Also they studied the effects of nonlinear clustering on one-point probability distribution functions of matter density and halo mass functions that previous linear approaches have failed to successfully reproduce. With Ji-sook Park, a research assistant, he also studied the galaxy formation model to populate simulated halos with galaxies. They applied an advanced method to the halo-galaxy correspondence model to recover observed galaxy luminosity functions from simulations.

Research Prof. Ho Seong Hwang made a cosmological test of the Lambda Cold Dark Matter (LCDM) model using the observed and simulated large-scale structures of the universe. Using the HectoMAP galaxy redshift survey and the Horizon Run 4 (HR4) simulation, he compared the physical properties of observed large-scale structures with those of simulated ones. He found that overall the size, richness and volume distributions of observed large-scale structures at intermediate redshifts are remarkably compatible with the predictions of the LCDM model.

Dr. Seokcheon Lee worked on the cross correlation of Rees-Sciama effect with weak lensing to investigate the properties of dark energy by using the improved standard perturbation theory. This method can be used for the new standard ruler.

Together with Profs. Changbom Park and Juhan Kim and using HR4 simulation data, Dr. L'Huillier is studying the interaction rate of dark matter haloes as well as the alignment of interacting haloes as a function of their environment. With Prof. David Mota (ITA, Norway), Dr. Hans Winther (Oxford) and Prof. Park, he is studying halo interactions in modified gravity.

Dr. Sungwook E. Hong, together with Prof. Park and Prof. Juhan Kim, developed a method to populate dark matter halos with mock galaxies within the HR4 simulation. He is also working on a conceptual design of a new multi-object spectroscopy system.

Dr. Xiao-Dong Li is continuing his work on the application of the Alcock-Pacyznski (AP) test to the large-scale structure. He published a paper on the redshift dependence of the AP effect on the galaxy 2-point correlation. He is now applying this method to SDSS-III observational data.

Dr. Hyunmi Song have worked on the study of correlation between quasar properties and background galaxy density using the SDSS data. She attended the 10th Marseille cosmology conference and the 29th IAU GA. She also visited IAC.

Dr. Raphael Gobat completed his study on the environmental signatures of low mass halos at z~2 on the properties of the galaxies they host. He finds that star formation in satellites of large star-forming galaxies at z~2 is inhibited through interaction with the hot gas retained by the host dark matter halo. In collaboration with Dr. S. Hong, he is investigating the link between cosmological evolution of galaxies and the number of star systems they host containing potentially habitable planets.

Dr. Fadia Salmi worked on the evolution of galaxy size at intermediate redshifts. She used the DLS field data and studied the different biases that could affect the results like the PSF, the size of the fitting region, the input noise image, the fitting methodology.

Dr. Stephen Appleby joined the astrophysics group in September 2015. He has been working with Professor Changbom Park on Minkowski functionals and their generalization. Along with Dr. Dhiraj Hazra (PCCP) and Dr. Spyros Sypsas (APCTP) he works to solve the non-linear Schroedinger equation on cosmological distance scales, to calculate the power spectrum for a dark matter candidate with non-linear pressure support.

Dr. Jihye Shin joined the astrophysics group in December 2015. With research Prof. Juhan Kim, she works on simulations to trace properties of low-mass stellar systems. She will also provide realistic sub-halo mass function for a virgo cluster-like halo using cosmological n-body simulations.