Neutral hydrogen (HI) intensity mapping traces the large-scale distribution of matter in the Universe and therefore should correlate with the gamma-ray emission originated from particle dark matter annihilation or from active galactic nuclei and star-forming galaxies, since the related processes occur in the same cosmic structures hosting HI. In this paper, we derive the cross-correlation signal between the brightness temperature of the 21-cm line emission of the HI spin-flip transition in the Universe and the unresolved gamma-ray background. Specifically, we derive forecasts for the cross-correlation signal by focussing on the opportunities offered by the combination of the Fermi-Large Area Telescope (LAT) gamma-ray sensitivity with the expectations of the HI intensity mapping measurements from future radio telescopes, for which we concentrate on the Square Kilometre Array (SKA) and MeerKAT, one of its precursors. We find that the combination of MeerKAT with the current Fermi-LAT statistics has the potential to provide a first hint of the cross-correlation signal originated by astrophysical sources, with a signal-to-noise ratio (SNR) of 3.7. With SKA Phase 1 and SKA Phase 2, the SNR is predicted to increase up to 5.7 and 8.2, respectively. The bounds on dark matter properties attainable with SKA combined with the current statistics of Fermi-LAT are predicted to be comparable to those obtained from other techniques able to explore the unresolved components of the gamma-ray background. The enhanced capabilities of SKA Phase 2, combined with a future generation gamma-ray telescope with improved specifications, can allow us to investigate the whole mass window for weakly interacting massive particles up to the TeV scale.

中文翻译：

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粒子暗物质间接探测的光谱协同效应：HI 强度映射如何满足伽马射线

中性氢 (HI) 强度映射追踪宇宙中物质的大规模分布，因此应该与源自粒子暗物质湮灭或活动星系核和恒星形成星系的伽马射线发射相关，因为相关过程发生在承载 HI 的相同宇宙结构中。在本文中，我们推导出了宇宙中 HI 自旋翻转跃迁的 21 厘米线发射的亮温与未解析的伽马射线背景之间的互相关信号。具体来说，我们通过关注费米大面积望远镜 (LAT) 伽马射线灵敏度与未来射电望远镜 HI 强度映射测量的预期相结合所提供的机会，得出对互相关信号的预测，为此，我们专注于平方公里阵列 (SKA) 和 MeerKAT，它的前身之一。我们发现 MeerKAT 与当前 Fermi-LAT 统计数据的结合有可能提供源自天体物理源的互相关信号的第一个线索，信噪比 (SNR) 为 3.7。在 SKA 阶段 1 和 SKA 阶段 2 中，SNR 预计分别增加到 5.7 和 8.2。用 SKA 结合 Fermi-LAT 的当前统计数据可获得的暗物质特性的界限预计与从其他能够探索伽马射线背景未解析成分的技术获得的界限相当。SKA Phase 2 的增强功能，结合具有改进规格的下一代伽马射线望远镜，