2017 Fiscal Year Annual Research Report
Understanding formation of supermassive black hole seeds at high-redshift via direct collapse
| Project/Area Number |
16H02163
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| Research Institution | Osaka University |
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Principal Investigator |
Shlosman Isaac 大阪大学, 理学研究科, 招へい教授 (40772405)
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| Co-Investigator(Kenkyū-buntansha) |
長峯 健太郎 大阪大学, 理学研究科, 教授 (50714086)
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| Project Period (FY) |
2016-04-01 – 2019-03-31
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| Keywords | Theoretical Astrophysics / Galaxy Formation / Cosmology / Direct Collapse / Fluid dynamics / Radiation transfer / Numerical simulations |
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| Outline of Annual Research Achievements |
Direct collapse within dark matter (DM) halos is a promising path to form supermassive black hole (SMBH) seeds at high redshifts. The innermost region of the collapse is expected to become optically thick and requires us to follow the radiation field in order to understand its subsequent evolution. So far, the adiabatic approximation has been used exclusively for this purpose. We apply radiative transfer in the flux-limited diffusion (FLD) approximation to solve the evolution of coupled gas and radiation, for isolated halos. For direct collapse within isolated DM halos, we find that (1) the photosphere forms at 1e-6 pc and rapidly expands outward. (2) A central core forms, with a mass of ~1 solar mass, supported by thermal gas pressure gradients and rotation. (3) Growing thermal gas and radiation pressure gradients dissolve it. (4) This process is associated with a strong anisotropic outflow, and another core forms nearby and grows rapidly. (5) Typical radiation luminosity emerging from the photosphere encompassing these cores is ~ 1e+38 erg/s, of order the Eddington luminosity. (6) Adiabatic models have been run for comparison and their evolution differs profoundly from that of the FLD models, by forming a central geometrically-thick disk. Overall, an adiabatic equation of state is not a good approximation to the advanced stage of direct collapse, mainly because the radiation is capable to escape due to a local anisotropy in the optical depth and associated gradients.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
We are achieving originally planned science goals, have published papers in a professional journal, and have given many presentations at conferences/workshops regarding our scientific progress.
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| Strategy for Future Research Activity |
We will apply the FLD radiation transfer with Enzo AMR code to the direct collapse in cosmological initial conditions, and examine the impact of radiation transfer. We will examine the growth of the central core after it becomes optically thick, and follow it until it becomes massive enough to be called a candidate of direct collapse gas sphere. We will then consider the impact of Lyman-alpha radiation transfer and its pressure effects. Due to the anisotropic nature of the inflow/outflow, it's possible that the Ly-a radiation escapes to the bipolar direction.
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