A Direct Detection of Neutral Hydrogen Intensity Mapping on Mpc Scales at z ≈ 0.32 and z ≈ 0.44

Abstract We report the detection of the cosmological power spectrum using the intensity mapping signal from 21 cm emission of neutral hydrogen (H I ), derived from interferometric observations with the L -band receivers of the MeerKAT radio telescope. Intensity mapping is a promising technique to map the three-dimensional matter distribution of the Universe at radio frequencies and probe the underlying cosmology. So far, detections have only been achieved through cross-correlations with galaxy surveys. Here we present independent measurements of the H I power spectrum at redshifts 0.32 and 0.44 with the foreground avoidance method. We utilize two distinct frameworks for mitigating systematics: a conservative baseline-flagging-based approach achieves detections at 3.2 σ and 3.5 σ , and a power-spectrum-based flagging method enhances the significance to 5.9 σ and 9.18 σ , respectively. The information contained in the power spectrum measurements allows us to probe the parameters of the H I mass function and H I halo model. These results are a significant step toward precision cosmology with H I intensity mapping using the new generation of radio telescopes.