星族III星形成的辐射调节
Radiative Regulation of Population III Star Formation
摘要：
我们探讨紫外线（UV）辐射的影响，从大规模的第三族（Pop III）的恒星25，40，80，和120 M_太阳对随后的Pop III恒星的形成。本文特别关注辐射反馈对源Pop III星质量的依赖性。来自源星的紫外线辐射可以通过光加热和光解离过程阻碍次级恒星的形成。最近，Susa & Umemura（2006）的研究表明，在120$M_sun的PopIII星中，电离辐射可以抵消H_2离解辐射的负效应，因为电离锋前形成的H_2壳层可以有效地屏蔽H_2离解辐射。另一方面，当源星质量较小时，由于H_2离解光子数与电离光子数的比值变大，H_2离解辐射的负反馈可能占主导地位。为了研究小质量恒星的辐射反馈效应，我们进行了三维辐射流体动力学模拟，包括电离辐射和H_2离解辐射的辐射转移效应。结果表明，当源星质量小于~25M_sun时，电离辐射不能抑制H_2离解辐射的负反馈。因此，这些质量较小的恒星周围的云的命运完全取决于来自源星的H_2离解辐射通量。通过对H_2壳层的形成及其屏蔽效应的解析估计，导出了辐射流体动力学反馈依赖于源星质量的判据。
英文摘要：
We explore the impact of ultraviolet (UV) radiation from massive Population III (Pop III) stars of 25, 40, 80, and 120 M_sun on the subsequent Pop III star formation. In this paper, particular attention is paid to the dependence of radiative feedback on the mass of source Pop III star. UV radiation from the source star can work to impede the secondary star formation through the photoheating and photodissociation processes. Recently, Susa & Umemura (2006) have shown that the ionizing radiation alleviates the negative effect by H_2-dissociating radiation from 120$M_sun PopIII 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 ~25M_sun, the ionizing radiation cannot suppress the negative feedback of H_2-dissociating radiation. Therefore, the fate of the neighboring clouds around such less massive stars is determined solely by the flux of H_2-dissociating radiation from source stars. With 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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