ACP Seminar (Astronomy - Cosmology - Particle Physics)

Speaker: Yidong Xu (Chinese Academy of Sciences)
Title: The Direct Collapse Black Holes during the Early EoR and the Neutral Islands during the Late EoR
Date (JST): Thu, Jul 24, 2014, 13:30 - 14:30
Place: Seminar Room A
Related File: 1232.pdf
Abstract: The observed fluctuations of the source-subtracted near-infrared background (NIRB) are > 10 times higher than expected from distant galaxies below the detection limit and first stars. In the first part of this talk, we will propose a novel interpretation in which early, intermediate-mass, accreting direct collapse black holes (DCBHs) could explain the observed fluctuations. We find that a population of highly obscured DCBHs formed in metal-free haloes with virial temperature 104 K at z >~ 12 can explain the observed level of the 3.6 and 4.5 μm fluctuations on scales > 100 arcsec. Albeit Compton-thick, at scales θ > 100 arcsec DCBHs also produce a cosmic X-ray background (0.5–2 keV)-NIRB (4.5 μm) cross-correlation signal that is in agreement with the recent measurements. The intermediate masses of DCBHs make them excellent seeds for the SMBHs observed at z >~ 6.
In the second part of this talk, we will discuss the nature and distribution of large neutral regions during the late epoch of reionization (EoR). Based on the excursion set model, we develop a method to predict the distribution of large scale neutral regions during the late stage of reionization, taking into account the ionizing background after the percolation of HII regions. The large scale neutral regions which we call "neutral islands" are not individual galaxies or minihalos, but larger regions where fewer galaxies formed and hence ionized later, and they are identified in the excursion set model with the first down-crossings of the island barrier. We also take the "bubbles-in-island" effect into account, and obtained the size distribution of the neutral islands. An additional barrier is set to avoid islands being percolated through. We will present our model results of neutral islands scales, their evolution, and the late reionization process.