发表机构
INAF – Osservatorio Astronomico di Trieste; Dipartimento di Fisica "G. Occhialini", Università degli Studi di Milano-Bicocca; Department of Physics and Astronomy, University of California, Riverside; Cahill Center for Astrophysics, California Institute of Technology; Institute for Cosmic Ray Research, The University of Tokyo; Kapteyn Astronomical Institute, University of Groningen; Department of Physics, Informatics and Mathematics, University of Modena and Reggio Emilia（意大利国家天体物理研究所的里雅斯特天文台; 米兰比可卡大学G. Occhialini物理系; 加州大学河滨分校物理与天文学系; 加州理工学院卡希尔天体物理学中心; 东京大学宇宙射线研究所; 格罗宁根大学卡普坦天文研究所; 摩德纳和雷焦艾米利亚大学物理、信息学与数学系）
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CLOUDY模拟和观测数据，利用Lya、HeII和Ha发射约束z>2类星体冷CGM的密度分布，发现宽对数正态分布可解释低HeII/Ha比，为理论模型提供比较基础。
AI 中文摘要
高红移类星体周围常规探测到扩展的Lya发射，揭示了巨大的冷星系周介质（CGM）储库。其共振性质使气体密度、电离状态和运动学的解释复杂化，因此HeII和Ha等非共振示踪剂至关重要。扩展先前的解析模型，我们使用CLOUDY光致电离模拟来预测类星体照射气体中的HeII/Ha，覆盖广泛参数范围，包括对数正态密度分布。该比率约束密度涨落，通常用团块因子C量化。我们将模型与z~2.1-4.5类星体周围的扩展Lya、HeII和Ha观测进行比较。在z~2.2，我们用Keck/KCWI观测了13个类星体，并用Keck/MOSFIRE针对具有最显著扩展Lya和HeII发射的系统，提供了首个结合Lya、HeII和Ha测量的统计性类星体-CGM样本。在匹配的至~35 pkpc孔径内，叠加光谱给出Lya/Ha=9.1，HeII/Ha=0.54，HeII/Lya=0.06。单密度模型需要非常高的CGM密度（n>10 cm^-3）或不可信的软AGN光谱才能重现低HeII/Ha比。宽对数正态密度分布反而在较低中值密度下重现该比率，但需要显著的发射加权高密度尾部，在我们的参数化中形式上对应C~10^3-10^4。我们还分析了3.1<z<4.5的26个VLT/MUSE类星体，其中Ha无法从地面观测，发现14个系统具有共空间的扩展Lya和HeII发射。探测到的发射加权HeII/Lya成分在z~2.2和z~3.7之间没有显示出强演化的证据，尽管这并不意味着底层密度PDF不变。这些约束为比较理论模型和模拟塑造高红移类星体CGM物理过程的流体动力学模拟提供了基础。
英文摘要
Extended Lya emission is routinely detected around high-redshift quasars, revealing large reservoirs of cool circumgalactic medium (CGM). Its resonant nature complicates interpretation of gas density, ionization state, and kinematics, making non-resonant tracers such as HeII and Ha essential. Extending previous analytical models, we use CLOUDY photo-ionization simulations to predict HeII/Ha in quasar-illuminated gas over a broad parameter range, including log-normal density distributions. The ratio constrains density fluctuations, commonly quantified by the clumping factor C. We compare the models with extended Lya, HeII, and Ha observations around quasars at z~2.1-4.5. At z~2.2, we observed 13 quasars with Keck/KCWI and targeted the systems with the most prominent extended Lya and HeII emission with Keck/MOSFIRE, providing the first statistical quasar-CGM sample with combined Lya, HeII, and Ha measurements. Within matched apertures out to ~35 pkpc, stacked spectra give Lya/Ha=9.1, HeII/Ha=0.54, and HeII/Lya=0.06. Single-density models require very high CGM densities (n>10 cm^-3) or implausibly soft AGN spectra to reproduce the low HeII/Ha ratio. Broad log-normal density distributions instead reproduce it at lower median densities but require a substantial emissivity-weighted high-density tail, corresponding formally to C~10^3-10^4 in our parameterization. We also analyze 26 VLT/MUSE quasars at 3.1<z<4.5, where Ha is inaccessible from the ground, finding 14 systems with co-spatial extended Lya and HeII emission. The detected, emission-weighted HeII/Lya component shows no evidence for strong evolution between z~2.2 and z~3.7, though this does not imply an invariant underlying density PDF. These constraints provide a basis for comparison with theoretical models and hydrodynamical simulations of the physical processes shaping quasar CGM at high redshift.
Comments21 pages, 15 figures, 6 tables in total, including an 8-page appendix with 9 figures and 5 tables. Submitted to A&A on 6 August 2026
