重子港的 COS 吸收调查：通过多相贝叶斯电离建模揭示环星系气体的物理条件,Monthly Notices of the Royal Astronomical Society

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重子港的 COS 吸收调查：通过多相贝叶斯电离建模揭示环星系气体的物理条件
Monthly Notices of the Royal Astronomical Society ( IF 4.8 ) Pub Date : 2020-11-25 , DOI: 10.1093/mnras/staa3544
Karl J Haislmaier ₁ , Todd M Tripp ₁ , Neal Katz ₁ , J Xavier Prochaska ₂ , Joseph N Burchett ₃ , John M O’Meara ₄ , Jessica K Werk ₅

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类星体吸收系统编码了大量关于星系间和星系周围介质中的丰度、电离结构和物理条件的信息。简单（通常是单相）光电离模型经常用于解码此类数据。使用来自重子港 COS 吸收调查 (CASBaH) 的五个离散吸收体，这些吸收体表现出广泛的检测离子（例如，Mg II、S II--S VI、O II--O VI、Ne VIII），我们展示了几个单相电离模型无法再现完整的一组测量柱密度的示例。为了探索可以自洽地解释不同离子的测量和运动学对齐的模型，我们开发了一个贝叶斯多相电离建模框架，该框架通过其独特的物理条件来表征离散相，并研究 UV 通量场、金属丰度和相对丰度的形状变化。我们的模型需要至少两个（但有利于三个）不同的电离相，范围从 $T \approx 10^{4}$ K 光电离气体到 $T \lesssim 10^{5.8}$ K 的暖热相。对于某些离子，一个明显的单一吸收“成分”包括来自多个相的贡献，并且高达 30% 的 HI 不是来自最低电离相。如果我们假设所有的相都被光电离，我们就无法找到热压平衡的解决方案。然而，通过引入更热的碰撞电离相，我们可以实现平衡的压力。最好的模型表明中等金属度，

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The COS Absorption Survey of Baryon Harbors: Unveiling the Physical Conditions of Circumgalactic Gas through Multiphase Bayesian Ionization Modeling

Quasar absorption systems encode a wealth of information about the abundances, ionization structure, and physical conditions in intergalactic and circumgalactic media. Simple (often single-phase) photoionization models are frequently used to decode such data. Using five discrete absorbers from the COS Absorption Survey of Baryon Harbors (CASBaH) that exhibit a wide range of detected ions (e.g., Mg II, S II--S VI, O II--O VI, Ne VIII), we show several examples where single-phase ionization models cannot reproduce the full set of measured column densities. To explore models that can self-consistently explain the measurements and kinematic alignment of disparate ions, we develop a Bayesian multiphase ionization modeling framework that characterizes discrete phases by their unique physical conditions and also investigates variations in the shape of the UV flux field, metallicity, and relative abundances. Our models require at least two (but favor three) distinct ionization phases ranging from $T \approx 10^{4}$ K photoionized gas to warm-hot phases at $T \lesssim 10^{5.8}$ K. For some ions, an apparently single absorption "component" includes contributions from more than one phase, and up to 30% of the H I is not from the lowest ionization phase. If we assume that all of the phases are photoionized, we cannot find solutions in thermal pressure equilibrium. By introducing hotter, collisionally ionized phases, however, we can achieve balanced pressures. The best models indicate moderate metallicities, often with sub-solar N/$\alpha$, and, in two cases, ionizing flux fields that are softer and brighter than the fiducial Haardt & Madau UV background model.

更新日期：2020-11-25

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