发表机构
Università degli Studi di Milano-Bicocca; INAF – Osservatorio Astronomico di Trieste; Leiden University; University of Groningen; New York University Abu Dhabi; Università degli Studi dell’Insubria; INFN, Sezione di Milano-Bicocca（米兰比可卡大学; 意大利国家天体物理研究所的里雅斯特天文台; 莱顿大学; 格罗宁根大学; 纽约大学阿布扎比分校; 因斯布鲁克大学; 意大利国家核物理研究所米兰比可卡分部）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究通过对比MUSE观测与模拟，发现类星体CGM密度分布比模拟预测更致密且更团块，需更高分辨率或额外物理机制来解释观测结果。
AI 中文摘要
冷星系周介质（CGM）的小尺度密度分布在星系演化中起着核心作用，但至今仍知之甚少。我们通过将MUSE对$z \sim 3.8$类星体（QSO）星云的CGM发射观测与基于新DaLya模拟套件在最大荧光假设下生成的模拟观测进行比较，为冷CGM密度分布提供了新的约束。此外，还补充了由COLIBRE（m5和m6分辨率）及HELLO模拟生成的模拟观测。我们首先研究了观测和模拟的Ly$\alpha$表面亮度（SB）值的分布，该分布在我们的假设下直接取决于冷气体密度分布，发现观测结果与模拟提供的上限之间存在显著差异，但COLIBRE较高分辨率运行（m5）除外。观测通常显示具有相对较大Ly$\alpha$ SB值的区域覆盖比例更高，并表明在50至200 ckpc的径向距离内，类星体CGM中必须存在至少达到10 cm$^{-3}$的密度。为理解这一差异的起源，我们研究了冷CGM密度分布，发现所有情况下的模拟PDF均与偏斜对数正态分布一致，其中位数约为$10^{-2}$ cm$^{-3}$，团块因子在16至102之间。我们将这些分布的宽度与观测到的HeII/Ly$\alpha$ CGM比值所隐含的宽度进行比较，该比值不依赖于最大荧光假设。假设对数正态PDF的中位数与模拟相似，观测比值要求更宽的PDF，其团块因子至少比模拟预测大8倍。这些结果表明，需要更高分辨率和/或额外的物理机制来重现这些红移处类星体的观测CGM。
英文摘要
The small scale density distribution of the cold circumgalactic medium (CGM) plays a central role in galaxy evolution, yet it is still poorly understood. We provide new constraints on the cold CGM density distribution by comparing the CGM emission from MUSE observations of quasar (QSO) nebulae at $z \sim 3.8$ with mock observations generated from the new DaLya simulation suite under the assumption of maximal fluorescence. These are further complemented by mock observations generated from the COLIBRE (m5 and m6 resolutions) and HELLO simulations. We first investigate the distribution of the observed and simulated Ly$α$ surface brightness (SB) values, which directly depend on the cold gas density distribution under our assumption, finding stark differences between observations and upper limits provided by simulations with the exception of the COLIBRE higher-resolution run (m5). The observations generally show a much larger covering fraction of regions with relatively large Ly$α$ SB values and suggest that densities reaching at least 10 cm$^{-3}$ must be present in the CGM of QSOs within a radial distance of 50 to 200 ckpc. To understand the origin of this discrepancy, we study the cold CGM density distribution finding in all cases simulated PDFs consistent with skewed lognormal ones with medians $\sim 10^{-2}$ cm$^{-3}$ and clumping factors between 16 and 102. We compare the broadness of these distributions to the one implied by the observed HeII/Ly$α$ CGM ratio, which is independent on the assumption of maximum fluorescence. Assuming lognormal PDFs with median values similar to the simulations, the observed ratio requires a broader PDF with a clumping factor at least 8 times larger than predicted by simulations. These results suggest that higher resolution and/or additional physical mechanisms are needed to reproduce the observed CGM of QSOs at these redshifts.
Comments13 pages + 4 appendix pages, 7 + 6 figures, submitted to A&A
