Achievements & Publications

The effects of radiative transfer on the reionization of an inhomogeneous universe

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Nakamoto, Taishi,   Umemura, Masayuki,   Susa, Hajime

Assuming simple dynamics for the growth of density fluctuations, we implement six-dimensional (6D) radiative transfer calculations to elucidate the effects of photon propagation during the reionization of an inhomogeneous universe. The ionizing sources are postulated to be AGN-like in this paper. The present simulations reveal that radiative transfer effects are...

On the Initial Mass Function of Population III Stars

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Nakamura, Fumitaka,   Umemura, Masayuki

The collapse and fragmentation of filamentary primordial gas clouds are explored using one- and two-dimensional hydrodynamical simulations coupled with the nonequilibrium processes of hydrogen molecule formation. The cloud evolution is computed from the initial central density n$_c$=10-10$^6$ cm$^-3$. The simulations show that depending on the initial density, there are two...

Ultraviolet-background-induced bifurcation of galactic morphology

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Susa, Hajime,   Umemura, Masayuki

Based upon a novel paradigm of galaxy formation under the influence of an ultraviolet background, the evolutionary bifurcation of pre- galactic clouds is compared with observations of elliptical and spiral galaxies. The theory predicts that the dichotomy between dissipational and dissipationless galaxy formation stems from the degree of self-shielding from...

Formation of Primordial Galaxies under Ultraviolet Background Radiation

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Susa, Hajime,   Umemura, Masayuki

The pancake collapse of pregalactic clouds under UV background radiation is explored with a one-dimensional sheet model. Here, attention is concentrated on elucidating the basic physics on the thermal evolution of pregalactic clouds exposed to diffuse UV radiation. So, we treat accurately the radiation transfer for the ionizing photons, with...

Radiation-hydrodynamical collapse of pre-galactic clouds in the ultraviolet background

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Kitayama, T.,   Tajiri, Y.,   Umemura, M.,   Susa, H.,   Ikeuchi, S.

To explain the effects of the ultraviolet (UV) background radiation on the collapse of pre-galactic clouds, we implement a radiation- hydrodynamical calculation, combining one-dimensional spherical hydrodynamics with an accurate treatment of the radiative transfer of ionizing photons. Both absorption and scattering of UV photons are explicitly taken into account. It...

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The effects of radiative transfer on the reionization of an inhomogeneous universe

Nakamoto, Taishi,   Umemura, Masayuki,   Susa, Hajime

Assuming simple dynamics for the growth of density fluctuations, we implement six-dimensional (6D) radiative transfer calculations to elucidate the effects of photon propagation during the reionization of an inhomogeneous universe. The ionizing sources are postulated to be AGN-like in this paper. The present simulations reveal that radiative transfer effects are...

March 2001   Monthly Notices of the Royal Astronomical Society
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On the Initial Mass Function of Population III Stars

Nakamura, Fumitaka,   Umemura, Masayuki

The collapse and fragmentation of filamentary primordial gas clouds are explored using one- and two-dimensional hydrodynamical simulations coupled with the nonequilibrium processes of hydrogen molecule formation. The cloud evolution is computed from the initial central density n$_c$=10-10$^6$ cm$^-3$. The simulations show that depending on the initial density, there are two...

February 2001   The Astrophysical Journal
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Ultraviolet-background-induced bifurcation of galactic morphology

Susa, Hajime,   Umemura, Masayuki

Based upon a novel paradigm of galaxy formation under the influence of an ultraviolet background, the evolutionary bifurcation of pre- galactic clouds is compared with observations of elliptical and spiral galaxies. The theory predicts that the dichotomy between dissipational and dissipationless galaxy formation stems from the degree of self-shielding from...

August 2000   Monthly Notices of the Royal Astronomical Society
Image

Formation of Primordial Galaxies under Ultraviolet Background Radiation

Susa, Hajime,   Umemura, Masayuki

The pancake collapse of pregalactic clouds under UV background radiation is explored with a one-dimensional sheet model. Here, attention is concentrated on elucidating the basic physics on the thermal evolution of pregalactic clouds exposed to diffuse UV radiation. So, we treat accurately the radiation transfer for the ionizing photons, with...

July 2000   The Astrophysical Journal
Image

Radiation-hydrodynamical collapse of pre-galactic clouds in the ultraviolet background

Kitayama, T.,   Tajiri, Y.,   Umemura, M.,   Susa, H.,   Ikeuchi, S.

To explain the effects of the ultraviolet (UV) background radiation on the collapse of pre-galactic clouds, we implement a radiation- hydrodynamical calculation, combining one-dimensional spherical hydrodynamics with an accurate treatment of the radiative transfer of ionizing photons. Both absorption and scattering of UV photons are explicitly taken into account. It...

June 2000   Monthly Notices of the Royal Astronomical Society