2016.1 ~ 2016.12

The Astrophysics and Cosmology group is headed by Prof. Changbom Park and Research Profs. Juhan Kim and Ho Seong Hwang. There are seven research fellows: Dr. Xiao-Dong Li, Dr. Hyunmi Song, Dr. Raphael Gobat, Dr. Stephen Appleby, Dr. Jihye Shin, Owain Snaith, and Dr. Motonari Tonegawa.

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 Dark Energy Spectroscopic Instrument (DESI) consortium, which plans to construct a new wide-field multi-object spectrograph to carry out dark energy-related survey sciences. He has worked 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 2016. Research Prof. Juhan Kim has been rebuilding the cosmological N-body simulation code (GOTPM). He adopted the Recursive Multi-Section technique to determine the local domain shape for better computing and network performances. He is also studying the cosmic matter-density evolution by solving the Euler equation analytically and numerically in the Lagrangian space.

Research Prof. Ho Seong Hwang made a cosmological test of the Lambda Cold Dark Matter (LCDM) model by comparing the physical properties of large-scale structures of the universe between observations and simulations. He used the HectoMAP galaxy redshift survey and the Horizon Run 4 simulation for the comparison, and found that the size, richness and volume distributions of observed large-scale structures at intermediate redshifts are remarkably similar to the predictions of the LCDM model. He also tested the cosmic variance of galaxy number counts and examined the evolution of scaling relations for quiescent galaxies using the SHELS galaxy redshift survey.

Dr. Sungwook E. Hong, who has move to KASI in December, published a paper on the properties of simulated galaxies from the Horizon Run 4 simulation, and worked with Dr. H. Song and Prof. C. Park to generate a mock AGN sample. Together with Dr. R. Gobat, he also published a paper on the evolution of galactic habitability in the universe. He is working on the conceptual design of a fiber-fed multi-object spectroscopy suitable for the Giant Magellan Telescope, as well as some instrumental collaborations with AAO in Australia and IUCAA in India.

Dr. Xiao-Dong Li and Prof. Park applied the Alcock-Pacyznski (AP) test to the Sloan Digital Sky Survey III galaxies and put very tight cosmological constraints on cosmological parameters such as the density parameter and dark energy equation of state. Dr. Li is also working on a project using the shape of the 2-point correlation function across the line of sight to constrain the cosmological parameters from the volume effect, and another project applying the AP test using the 3-point correlation function.

Dr. Hyunmi Song and Prof. Park have been trying to plant quasars in dark matter halos of a cosmological N-body simulation, Horizon Run 4, to generate mock quasar catalogs. Dr. Hyunmi Song, Prof. Ho Seong Hwang, and Prof. Park worked on the MMT/Hectospec redshift data in the field of the Abell 2199 cluster, and analyzed the spatial and kinematic distributions of the cluster galaxies in comparison with the ICM of the cluster using the Suzaku X-ray data.

Dr. Raphael Gobat and Dr. S. Hong have worked on semi-analytic models of planetary distribution functions in galaxies across cosmic time, with an emphasis on habitable terrestrial planets. Dr. Raphael Gobat has also studied star formation rates and stellar population gradients in early-type galaxies at z>1.5. This represents the first direct confirmation of inside-out quenching in high-redshift non-star forming galaxies.

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, together with Prof. Park, Prof. Kim, and Dr. Snaith, is preparing a large-volume and high-resolution hydrodynamic simulation, to be called Horizon Run 5. She published a paper on the low-end mass function of the Quintuplet cluster. She finished a project on hydrodynamic simulations of the central molecular zone with a realistic Galactic potential.

Dr. Owain Snaith, along with Prof. Kim and Prof. Park, has studied the evolution of the gas power spectrum in cosmological simulations, especially how the power spectrum evolves depending on the resolution of the simulation initial conditions. He is working with Dr. J. Shin on a parameter study in order to tune the simulation code to observations, ready for the Horizon Run 5 simulation later in the year. He is studying dark matter halos in the Illustris simulation and is interested in exploring the chemical evolution of galaxies in simulations using a variety of approaches.

Dr. Motonari Tonegawa, a new research fellow arrived at KIAS on December 1st, works on research topics such as the large-scale structure of the Universe, observational cosmology, and redshift surveys. He tries to measure the velocity dispersion of galaxies in virialized systems and its redshift evolution, through the Finger-of-God effect seen in the two-point correlation function of MMT spectroscopic sample, to compare with the prediction of General Relativity and other cosmology models.