研究実績の概要 |
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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今後の研究の推進方策 |
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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