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arXiv 2302.00692astro-ph.GA
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低红移成星星系的冷环星系介质：I --经验模型和平均性质

The cool circumgalactic medium of low-redshift star-forming galaxies: I -- Empirical model and mean properties

Yakov Faerman, Jessica K. Werk

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Submitted to ApJ, 17 pages + appendices, comments welcome
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摘要：

本文提出了一个冷的、$T \approx 10^4$ K环星系介质（CGM）的解析模型，描述了CGM的气体分布、热态和电离态。我们的模型假设（总）压力平衡与环境温暖/热CGM，光电离的超星系辐射场，并允许非热的压力支持，参数化的热压力比，$η= P_{\rm hot,th}/P_{\rm cool,th}$。我们将该模型应用于COS-Halos数据集，发现一个标称模型与$η= 3$，气体分布到$r \approx 0.6 R_{\rm vir}$，和$M_{\rm cool} = 3 \times 10^9~{\rm M_{\odot}}$，对应于体积填充分数的$f_{\rm V,cool} \approx 1\%$，再现HI和低/中间金属离子（CII，CIII，SiII，SiIII，MgII）的平均测得的柱密度。在非热压力或气体质量中的$\pm 0.5$ dex的变化包括物体之间散射的$\sim 2/3$。我们的标称模型生产不足的测量CIV和SiIV列，我们表明，这些可以再现与（i）一个冷却阶段与$M_{\rm cool} \approx 10^{10}~{\rm M_{\odot}}$和$η\approx 5$，或（ii）在中间温度下，冷却或混合气体的附加组件，与$M \approx 1.5 \times 10^{10}~{\rm M_{\odot}}$和占用$\sim 1/2$的总CGM体积。对于具有$f_{\rm V,cool} \approx 1\%$的冷气体，我们提供了云大小的上限，$R_{\rm cl} \lesssim 0.5$ kpc。我们的研究结果表明，对于平均星系CGM，在冷却阶段的质量和非热支持低于估计在以前的作品，和极端的情况下，星系反馈和非热支持可能是不必要的。我们估计了冷气体耗尽和补充的速率，并发现星系上的吸积可以完全被冷凝、流出和IGM吸积所抵消，从而允许$\dot{M}_{\rm cool}\sim0$在长时间尺度上存在。

英文摘要：

We present an analytic model for the cool, $T \approx 10^4$ K, circumgalactic medium (CGM), describing the gas distribution, thermal and ionization state. Our model assumes (total) pressure equilibrium with the ambient warm/hot CGM, photoionization by the metagalactic radiation field, and allows for non-thermal pressure support, parametrized by the ratio of thermal pressures, $η= P_{\rm hot,th}/P_{\rm cool,th}$. We apply the model to the COS-Halos data set and find that a nominal model with $η= 3$, gas distribution out to $r \approx 0.6 R_{\rm vir}$, and $M_{\rm cool} = 3 \times 10^9~{\rm M_{\odot}}$, corresponding to a volume filling fraction of $f_{\rm V,cool} \approx 1\%$, reproduces the mean measured column densities of HI and low/intermediate metal ions (CII, CIII, SiII, SiIII, MgII). Variation of $\pm 0.5$ dex in the non-thermal pressure or gas mass encompasses $\sim 2/3$ of the scatter between objects. Our nominal model underproduces the measured CIV and SiIV columns, and we show these can be reproduced with (i) a cool phase with $M_{\rm cool} \approx 10^{10}~{\rm M_{\odot}}$ and $η\approx 5$, or (ii) an additional component at intermediate temperatures, of cooling or mixing gas, with $M \approx 1.5 \times 10^{10}~{\rm M_{\odot}}$ and occupying $\sim 1/2$ of the total CGM volume. For cool gas with $f_{\rm V,cool} \approx 1\%$ we provide an upper limit on the cloud sizes, $R_{\rm cl} \lesssim 0.5$ kpc. Our results suggest that for the average galaxy CGM, the mass and non-thermal support in the cool phase are lower than estimated in previous works, and extreme scenarios for galactic feedback and non-thermal support may not be necessary. We estimate the rates of cool gas depletion and replenishment, and find accretion onto the galaxy can be entirely offset by condensation, outflows, and IGM accretion, allowing $\dot{M}_{\rm cool}\sim0$ over long timescales.

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