研究成果・発表論文

Radiative regulation of Population III star formation

Hasegawa, K.,   Umemura, M.,   & Susa, H.


要旨
We explore the impact of ultraviolet (UV) radiation from massive Population III (Pop III) stars of 25, 40, 80 and 120M$_solar$ on the subsequent Pop III star formation. In this paper, particular attention is paid to the dependence of radiative feedback on the mass of source Pop III star. UV radiation from the source star can work to impede the secondary star formation through the photoheating and photodissociation processes. Recently, Susa and Umemura have shown that the ionizing radiation alleviates the negative effect by H$_2$-dissociating radiation from 120M$_solar$ Pop III star, since an H$_2$ shell formed ahead of an ionizing front can effectively shield H$_2$-dissociating radiation. On the other hand, it is expected that the negative feedback by H$_2$-dissociating radiation can be predominant if a source star is less massive, since a ratio of the H$_2$-dissociating photon number to the ionizing photon number becomes higher. In order to investigate the radiative feedback effects from such less massive stars, we perform three-dimensional radiation hydrodynamic simulations, incorporating the radiative transfer effect of ionizing and H$_2$-dissociating radiation. As a result, we find that if a source star is less massive than åisebox-0.5ex~25M$_solar$, the ionizing radiation cannot suppress the negative feedback of H$_2$-dissociating radiation. Therefore, the fate of the neighbouring clouds around such less massive stars is determined solely by the flux of H$_2$-dissociating radiation from source stars. By making analytic estimates of H$_2$ shell formation and its shielding effect, we derive the criteria for radiation hydrodynamic feedback depending on the source star mass.




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