Galaxies and groups of galaxies exist in dark-matter haloes filled with diffuse gas. The diffuse gas represents up to 80% of the mass in baryonic matter within the haloes^1,2, but is difficult to detect because of its low density (particle number densities of ≲10⁻⁴ cm⁻³) and high temperature (mostly >10⁶ K). Here we analyse the impact of diffuse gas associated with nearby galaxies using the dispersion measures (DMs) of extragalactic fast radio bursts (FRBs). FRB DMs provide direct measurements of the total ionized-gas contents along their sightlines. Out of a sample of 474 distant FRBs from the Canadian Hydrogen Intensity Mapping Experiment (CHIME) FRB Catalog 1 (ref. ³), we identify a subset of events that probably intersect the dark-matter haloes of galaxies in the local Universe (<40 Mpc). The mean DM of the galaxy-intersecting FRBs is larger than that of the non-intersecting FRBs with a probability >0.99 and the excess DM is >90 pc cm⁻³ with >95% confidence. The excess is larger than expected for the diffuse gas surrounding isolated galaxies, but may be explained by additional contributions from gas surrounding galaxy groups, including from the Local Group. This result demonstrates the predicted ability of FRBs to be used as sensitive, model-independent measures of the diffuse gas contents of dark-matter haloes^4,5,6,7.

星系和星系群存在于充满扩散气体的暗物质晕中。^{扩散气体在晕1,2}中占重子物质质量的 80% ，但由于其密度低（粒子数密度为≲ 10 ^-4  cm ^-3）和高温（大部分 > 10 ⁶  K)。在这里，我们使用河外快速射电暴 (FRB) 的色散测量 (DM) 分析与附近星系相关的扩散气体的影响。FRB DM 提供沿其视线的总电离气体含量的直接测量。来自加拿大氢强度测绘实验 (CHIME) FRB 目录 1 的 474 个遥远 FRB 样本中（参考文献 ³），我们确定了可能与本地宇宙中星系暗物质晕相交的事件子集（<40 Mpc）。与星系相交的快速射电暴的平均 DM 大于非相交的快速射电暴的概率 >0.99，过量 DM >90 pc cm ^-3且置信度 >95%。对于孤立星系周围的扩散气体，过量比预期的要大，但可以用星系群周围气体的额外贡献来解释，包括来自本星系群的气体。这一结果证明了 FRB 的预测能力，可用作对暗物质晕^4,5,6,7的扩散气体含量进行敏感、独立于模型的测量。