We present an analysis of the origin and properties of the circum-galactic medium (CGM) in a suite of 11 cosmological zoom simulations resembling present day spiral galaxies. On average the galaxies retain about 50\% of the cosmic fraction in baryons, almost equally divided into disc (interstellar medium) gas, cool CGM gas and warm-hot CGM gas. At radii smaller than 50 kpc the CGM is dominated by recycled warm-hot gas injected from the central galaxy, while at larger radii it is dominated by cool gas accreted onto the halo. The recycled gas typically accounts for one-third of the CGM mass. We introduce the novel publicly available analysis tool \textsc{pygad} to compute ion abundances and mock absorption spectra. For Lyman-${\alpha}$ absorption we find good agreement of the simulated equivalent width (EW) distribution and observations out to large radii. Disc galaxies with quiescent assembly histories show significantly more absorption along the disc major axis. By comparing the EW and HI column densities we find that CGM Lyman-${\alpha}$ absorbers are best represented by an effective line-width $b\approx 50 - 70$ km s$^{-1}$ that increases mildly with halo mass, larger than typically assumed.

中文翻译：

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Lyman-α 吸收超出了模拟螺旋星系的圆盘

我们在一套类似于当今螺旋星系的 11 个宇宙学缩放模拟中，对环银河介质 (CGM) 的起源和特性进行了分析。平均而言，星系在重子中保留了大约 50% 的宇宙分数，几乎相等地分为盘状（星际介质）气体、冷 CGM 气体和暖热 CGM 气体。在半径小于 50 kpc 的情况下，CGM 主要是从中央星系注入的回收暖热气体，而在较大的半径上，CGM 主要是吸积到晕上的冷气体。回收气体通常占 CGM 质量的三分之一。我们引入了新颖的公开可用分析工具 \textsc{pygad} 来计算离子丰度和模拟吸收光谱。对于 Lyman-${\alpha}$ 吸收，我们发现模拟等效宽度 (EW) 分布和观察到大半径的良好一致性。具有静止组装历史的盘状星系在盘状主轴上显示出明显更多的吸收。通过比较 EW 和 HI 列密度，我们发现 CGM Lyman-${\alpha}$ 吸收器最好由有效线​​宽 $b\approx 50 - 70$ km s$^{-1}$ 表示，该线宽温和增加具有晕质量，比通常假设的要大。