2016 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 | Cosmology / Structure Formation / Supermassive Black Hole / Galaxy Formation / Direct collapse scenario / Fluid dynamics / Numerical simulations / Star formation |
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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 ~ 10^-6 pc and rapidly expands outward. (2) A central core forms, with a mass of ~1 Msun, 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 ~ 10^38 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
For the first time in the world, we have succeeded in applying the FLD radiation transfer with Enzo AMR code to the direct collapse for SMBH seed formation. We have shown that the adiabatic approximation is not a good approximation, and the radiation transfer calculation should be performed for a reliable solution for gas dynamics in the inner part of direct collapse halo. It is also quite intriguing to see the outflow features due to radiation pressure.
The project is proceeding well as planned, and we are going to expand our work into the cosmological halos at high-redshift, and examine the angular momentum extraction mechanism in a more realistic environment where galaxy merger and dark matter halo dynamics are closely involved.
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| Strategy for Future Research Activity |
Having succeeded in applying the FLD radiation transfer with Enzo AMR code to the direct collapse in isolated halos, we will do the same for the cosmological initial conditions, and verify that the same conclusions apply for the high-redshift cosmological halos. The initial test runs seem promising, and we will be able to show for the first time that radiation transfer and pressure play important roles in the direct collapse scenario. We will attempt to run the simulation with a higher resolution and try to resolve the inner flow down to 10^-6 pc, where the photosphere seems to be appearing. We will further examine the role of radiation pressure, as well as the Lyman-alpha photon pressure if time allows.
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