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● 날짜 : 2015년 11월 24일 (화요일)
● 시간 : 16시 30분
● 장소 : 천문대 영상실
● 강사 : Dr. Hyunbae Park (Korea Astronomy and Space Science Institute)
Title :
Recombination in Intergalactic Medium during the Epoch of Reionization
Abstract :
Clumpiness of intergalactic medium in sub-Mpc scales can boost the recombination rate significantly, thereby affecting the growth of HII bubbles during the Epoch of Reionization (EoR). In this work, we use high-resolution hydrodynamic simulation with radiative-transfer
to assess clumpiness of ionized intergalactic medium extending the mass resolution well below 10^8 M_sun to take into account the structures that can form in pre-ionized medium with T< 10^4 K. This way, we attempts to provide a sub-grid prescription for unresolved
clumping factor for large-scale EoR simulations. During a few megayear after the volume is exposed to the radiation, small-scale structures lead to a large (C>10) clumping factor, thereby hugely boosting the recombination rate. Later (> 10 Myr), the hydrodynamic
feedback flattens out most of the density structures and the clumping factor converges to one. The integral effect of initially high clumpiness does lead to significantly more consumption of photons. When the UV radiation if J_21 = 1 arrives our sample volume at z = 8, for example, small-scales structures lead to 0.45 recombination per H atom in addition to what we expect from the background universe, 0.07 per H atom per 150 Myr. Having lower intensity for ionizing background leads to ionization fronts being trapped at lower densities. Then, self-shielding gas has less chance recombine when ionized. For lower z, more gas is collapsed in structures and, therefore, the net recombination rate is higher. We find a scaling relation of 0.32*(J_21^0.12)((1+z_i)/11)^-1.7 for the additional recombination.
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