Jow Dylan L, Wu Xiaohan, Pen Ue-Li
Canadian Institute for Theoretical Astrophysics, University of Toronto, Toronto, ON M5S 3H8, Canada.
Department of Physics, University of Toronto, Toronto, ON M5S 1A7, Canada.
Proc Natl Acad Sci U S A. 2024 Sep 24;121(39):e2406783121. doi: 10.1073/pnas.2406783121. Epub 2024 Sep 17.
We consider the refractive lensing effects of ionized cool ([Formula: see text]) gas cloudlets in the circumgalactic medium (CGM) of galaxies. In particular, we discuss the combined effects of lensing from these cloudlets and scintillation from plasma screens in the Milky Way interstellar medium (ISM). We show that, if the CGM comprises a mist of subparsec cloudlets with column densities of order [Formula: see text] (as predicted by [M. McCourt, S. P. Oh, R. O'Leary, A. M. Madigan, , 5407-5431 (2018)]), then fast radio bursts (FRBs) whose sightlines pass within a virial radius of a CGM halo will may be lensed into tens of refractive images with a ∼10 ms scattering timescale. When these images are formed, they will be resolved by scintillating screens in the Milky Way ISM and will suppress the observed scintillation. We illustrate this effect in refractive lensing and argue that positive detections of FRB scintillation may constrain the properties of these cool-gas cloudlets, with current scintillation observation weakly disfavoring the cloudlet model. We propose that sheet-like geometries for the cool gas in the CGM can reconcile quasar absorption measurements (from which we infer the presence of the cool gas with structure on subparsec scales) and the unexpected lack of lensing signals from this gas thus far observed.
我们考虑星系星系际介质（CGM）中电离冷（[公式：见原文]）气体小云的折射透镜效应。特别地，我们讨论了这些小云的透镜效应与银河系星际介质（ISM）中等离子体屏的闪烁效应的综合影响。我们表明，如果CGM由柱密度约为[公式：见原文]的亚秒差距小云组成（如[M. 麦考特、S. P. 奥、R. O'Leary、A. M. 马迪根， ，5407 - 5431（2018）]所预测），那么视线穿过CGM晕的质心半径内的快速射电暴（FRB）可能会被透镜化为数十个具有约10毫秒散射时标的折射图像。当这些图像形成时，它们将被银河系ISM中的闪烁屏分辨，并会抑制观测到的闪烁。我们在折射透镜效应中说明了这种效应，并认为对FRB闪烁效应的肯定探测可能会限制这些冷气体小云的性质，目前的闪烁观测结果对小云模型略有不利。我们提出，CGM中冷气体的片状几何形状可以协调类星体吸收测量结果（从中我们推断出存在具有亚秒差距尺度结构的冷气体）与迄今为止观测到的来自这种气体的意外缺乏透镜信号的情况。
