保持宇宙电离：星系际气体的光加热和高红移聚集因子
Keeping the Universe ionised: photoheating and the high-redshift clumping factor of the intergalactic gas
摘要：
维持星系际氢离子化所需的临界恒星形成率密度，主要取决于星系际介质（IGM）中再结合的平均速率。这个速率与聚集因子C = <rho_b^2> / avg（rho_b）^2成正比，其中rho_b和avg（rho_b）分别是局域和宇宙平均重子密度，括号< >表示IGM中重组气体的空间平均值。我们进行了一套宇宙学的光滑粒子流体动力学模拟，包括辐射冷却计算的体积加权聚集因子的IGM在红移z >= 6。我们调查的光电离加热均匀的紫外线背景的影响，并发现，光加热强烈地降低了成团因子的增加压力支持平滑小规模的密度波动。即使是我们对聚集因子C = 6的最保守估计，也比通常用于确定恒星形成星系保持z=6 IGM电离能力的聚集因子小五倍。我们的结果意味着，在z = 6时观测到的恒星形成星系的数量可能足以使IGM保持电离状态，前提是IGM在z >~ 9时被再加热，并且逃离恒星形成区域电离IGM的电离光子的比例大于0.25。
英文摘要：
The critical star formation rate density required to keep the intergalactic hydrogen ionised depends crucially on the average rate of recombinations in the intergalactic medium (IGM). This rate is proportional to the clumping factor C = <rho_b^2> / avg(rho_b)^2, where rho_b and avg(rho_b) are the local and cosmic mean baryon density, respectively, and the brackets < > indicate spatial averaging over the recombining gas in the IGM. We perform a suite of cosmological smoothed particle hydrodynamics simulations that include radiative cooling to calculate the volume-weighted clumping factor of the IGM at redshifts z >= 6. We investigate the effect of photoionisation heating by a uniform ultraviolet background and find that photoheating strongly reduces the clumping factor as the increased pressure support smoothes out small-scale density fluctuations. Even our most conservative estimate for the clumping factor, C = 6, is five times smaller than the clumping factor that is usually employed to determine the capacity of star-forming galaxies to keep the z=6 IGM ionised. Our results imply that the observed population of star-forming galaxies at z = 6 may be sufficient to keep the IGM ionised, provided that the IGM was reheated at z >~ 9 and that the fraction of ionising photons that escape star-forming regions to ionise the IGM is larger than 0.25.
机构、总结、中文摘要均由AI分析而来，可能存在错误，请以论文正文为准。
