We analyse the distribution and origin of OVI in the Circumgalactic Medium (CGM) of dark-matter haloes of $\sim 10^{12}$ M$_\odot$ at $z\sim1$ in the VELA cosmological zoom-in simulations. We find that the OVI in the inflowing cold streams is primarily photoionized, while in the bulk volume it is primarily collisionally ionized. The photoionized component dominates the observed column density at large impact parameters ($\gtrsim 0.3 R_{\rm vir}$), while the collisionally ionized component dominates closer in. We find that most of the collisional OVI, by mass, resides in the relatively thin boundaries of the photoionized streams. We discuss how the results are in agreement with analytic predictions of stream and boundary properties, and their compatibility with observations. This allows us to predict the profiles of OVI and other ions in future CGM observations and provides a toy model for interpreting them.

中文翻译：

---

OVI 在 z ∼ 1 大质量星系的宇宙学模拟中追踪具有碰撞电离边界的光电离流

我们在 VELA 宇宙学放大模拟中分析了 OVI 在 $\sim 10^{12}$ M$_\odot$ 暗物质晕环星系介质 (CGM) 中 $z\sim1$ 的分布和起源. 我们发现流入的冷流中的 OVI 主要是光电离的，而在大体积中它主要是碰撞电离。在大的冲击参数（$\gtrsim 0.3 R_{\rm vir}$）下，光离子化的成分在观察到的柱密度中占主导地位，而碰撞电离的成分在更近的地方占主导地位。我们发现，按质量计，大部分碰撞 OVI 位于光离子流的边界相对较薄。我们讨论结果如何与流和边界属性的分析预测一致，以及它们与观测的兼容性。