The Astrophysics and Cosmology Group is headed by Prof. Chang­born Park and Research Profs. Juhan Kim and Ena Choi. Postdocs in the group include Drs. Stephen Appleby, Motonari Tonegawa, Hyunsung Jun, Jaehyun Lee, Yonghwi Kim, Junsup Shim, Yongmin Yoon, Jaehong Park, Fuyu Dong, and Ankit Singh.

Prof. Park is carrying out the Korea Dark Energy Survey (KDES) program, which aims to uncover the nature of the dark energy component of the universe. He is leading the Korean Scientist Group (KSG) participating in the recently finished Sloan Digital Sky Survey (SDSS) IV. The MaNGA and eBOSS survey data are being analyzed. He is also a member of the Dark Energy Spec­troscopic Instrument [DESI) consortium, which plans to carry out a deeper redshift survey starting from 2021 . He is leading the Horizon Run 5 [HR5) collaboration. HR5 is a 1 Gpc-volume high resolution (1 pkpc) gravity/hydrodynamics simulation made by an international consortium of Korea, France, and U.K. He has also created a collaboration called the Narrow Band Imaging Survey Collaboration [NBIS) with Purdue, Rutgers, and KASI to observe the Lyman-a objects at high redshifts (2

Individual members of the Astrophysics and Cosmology Group were actively conducting their research in 2020. Research Prof. Juhan Kim has been postprocessing the Horizon Run 5 (HR5) simu­lation data to extract galaxies composed of dark matter, stars, gas, and active galactic nuclei (AGN). He studies the activities of super massive black holes (SMBHs) in the HR5 and compares the results with observations of SMBH demography. He is now collaborating with the Pulsar Timing Array (PTA) team to study long-term gravita­tional wave detection using the HR5 AGN merger history.

QUC Research Prof. Ena Choi studied the chemical enrichment of massive galaxies and their gaseous halos by analyzing high-reso­lution hydrodynamic simulations. By tracking simulation particles, she has found that AGN feedback via radiation-driven winds is capable of ejecting large amounts of metals from galaxies into their halos, resulting in better agreement with observed radial metallicity profiles. She also found that, according to both the simulations and observations, AGN are no more likely to be found in merging systems than in inactive galaxies.

Dr. Motonari Tonegawa studied small-scale redshift-space galaxy clustering using N-body simulations and observations, and found that small-scale clustering can tightly constrain the matter density parameter as well as the velocity bias of galaxies and the gal­axy-halo connection. He worked as a co-chair of the 9th KIAS workshop on Cosmology and Large-scale Structure. With current group members and alumni, new attempts and further effort have been made to conduct the meeting online to cope with the current pandemic. Dr Tonegawa finished his term at KIAS and moved to APCTP.

Dr. Hyunsung 」un studies the role of quasars in heating and pushing their host galaxy, attempting to connect the radiation pressure from the active nucleus known to be effective around parsec-scales to the outflows of gas and dust observed up to thousands of parsecs. He is investigating how massive quasars transport gas to the nucleus. Observing one extremely massive quasar at z=1.47 with a nar­row-band near-lR filter, he found a strong overdensity of star-form­ing, emission-line galaxies 2Mpc away, indicative of quasar activ­ity in massive galaxies happening in the outskirts of protoclusters.

Dr. Yonghwi Kim has been working on classifying and visualizing three-dimensional galaxy data in HR5 simulations and investigating the evolution of super massive black holes and its correlation with the local environment. He has studied the role of radiation pressure in observed luminous quasars and compared them with mock data in the HR5. He also has studied the evolution of disk galaxies in the Hubble sequence using magnetohydrodynamic simulations.

Dr. Jaehyun Lee has been working on HR5 post-processing, and generating galaxy and halo catalogues from the post-processed data. This is an essential step for research using HR5. He made movies to promote HR5 and motivate researchers. He is studying the formation and growth of proto clusters in HR5. He also investi­gated the impact of ram pressure on galaxies in galaxy-cluster-like environments using radiative transfer hydrodynamic simulations of very high spatial resolution.

Dr. Junsup Shim worked on identifying cosmic voids from the mat­ter density field so as to associate them with massive clusters of a particular mass scale by analyzing halo-antihalo pairs in a pair of initial condition inverted simulations. He also investigated the clustering properties of the critical points of density fields by meas­uring their two-point correlation functions and comparing them to the predictions for Gaussian random fields.

Dr. Yongmin Yoon studied star formation enhancement in barred disk galaxies in interacting clusters and the dependence of the Fun­damental Plane of early-type galaxies on age and internal struclure. He also investigated whether or not the frequency of tidal features correlates with the age and internal structure of early-type galaxies.

Dr. Jaehong Park joined the group in May 2020. He has been working on modelling Lyman alpha emitters (LAEs) in HR5 to inves­tigate the properties of LAEs and the relation between LAEs and their environment. This work is one of the activities of the NBIS collaboration. Dr. Park has also been studying the Epoch of Reion­ization, mainly focusing on inferring astrophysical (cosmological) properties from the 21-cm signal. He developed a calibration rec­ipe to correct the photon non-conservation problem that develops in most semi-numerical simulations that adopt the excursion set ap­proach to finding an ionizing map.

Dr. Fuyu Dong joined the group in July 2020. She has been study­ing the Alock-Paczynski test. She has measured the two-point correlation function based on the SDSS data, including the SDSS DR7, BOSS and eBOSS data. She also has been learning to define the galaxy samples in terms of stellar mass and magnitude.

Dr. Ankit Singh joined the group in November 2020. He is cur­rently working on the impact of the large-scale environment on AGNs. He has also been working on how the large-scale filament environment affects the properties of the galaxies residing in it at high redshift.