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arXiv 1808.01726astro-ph.GA
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辐射压力对致密恒星系统恒星形成效率和表面密度的限制

Radiation Pressure Limits on the Star Formation Efficiency and Surface Density of Compact Stellar Systems

Roland M. Crocker, Mark R. Krumholz, Todd A. Thompson, Holger Baumgardt, Dougal Mackey

摘要:

在年轻、大质量的星团中,大量的尘埃气体柱包围着恒星的形成,并为恒星的形成提供了燃料,这可能使这些系统在光学上变厚,以至于辐射到红外线。这提出了这样的前景,即由离开恒星表面的光子吸收产生的“直接”辐射压力和由尘埃颗粒吸收然后重新发射的光子产生的“间接”辐射压力可能是此类系统中反馈的重要来源。在这里,我们评估这种可能性,推导出的条件下,一个球状的,自引力,混合气体恒星云可以避免灾难性的破坏的直接和间接辐射压力的综合影响。我们发现,辐射压力设置一个最大的团簇形成效率的$ε_{\rm max} \sim 0.9$在(非常大的)气体表面密度的$\sim 10^5 M_\odot$ PC $^{-2} (Z_\odot/Z) \simeq 20$克厘米$^{-2} (Z_\odot/Z)$,但气体云超过这个限制进行显着的辐射驱动的膨胀在恒星形成过程中,导致最大恒星表面密度非常接近这个值的所有星团。致密恒星系统中心表面质量密度的数据,虽然稀疏和部分混淆的动力学效应,是广泛一致的金属依赖的上限比这个值的存在。我们的结果意味着,这个限制可能会妨碍形成的祖先的中等质量黑洞的系统与$Z \gtrsim 0.2 Z_\odot$。

英文摘要:

The large columns of dusty gas enshrouding and fuelling star-formation in young, massive stellar clusters may render such systems optically thick to radiation well into the infrared. This raises the prospect that both "direct" radiation pressure produced by absorption of photons leaving stellar surfaces and "indirect" radiation pressure from photons absorbed and then re-emitted by dust grains may be important sources of feedback in such systems. Here we evaluate this possibility by deriving the conditions under which a spheroidal, self-gravitating, mixed gas-star cloud can avoid catastrophic disruption by the combined effects of direct and indirect radiation pressure. We show that radiation pressure sets a maximum star cluster formation efficiency of $ε_{\rm max} \sim 0.9$ at a (very large) gas surface density of $\sim 10^5 M_\odot$ pc$^{-2} (Z_\odot/Z) \simeq 20$ g cm$^{-2} (Z_\odot/Z)$, but that gas clouds above this limit undergo significant radiation-driven expansion during star formation, leading to a maximum stellar surface density very near this value for all star clusters. Data on the central surface mass density of compact stellar systems, while sparse and partly confused by dynamical effects, are broadly consistent with the existence of a metallicity-dependent upper-limit comparable to this value. Our results imply that this limit may preclude the formation of the progenitors of intermediate-mass black holes for systems with $Z \gtrsim 0.2 Z_\odot$.

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