Browsing by Author "Li, Yichao"

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    H I intensity mapping with MeerKAT: Power spectrum detection in cross-correlation with WiggleZ galaxies
    (Oxford University Press, 2023) Cunnington, Steven; Li, Yichao; Santos, Mario G.
    We present a detection of correlated clustering between MeerKAT radio intensity maps and galaxies from the WiggleZ Dark Energy Survey. We find a 7.7σ detection of the cross-correlation power spectrum, the amplitude of which is proportional to the product of the HI density fraction (⁠ΩHI ⁠), HI bias (⁠bHI ⁠), and the cross-correlation coefficient (r). We therefore obtain the constraint ΩHIbHIr=[0.86±0.10(stat)±0.12(sys)]×10−3 ⁠, at an effective scale of keff ∼ 0.13hMpc−1 ⁠. The intensity maps were obtained from a pilot survey with the MeerKAT telescope, a 64-dish pathfinder array to the SKA Observatory (SKAO). The data were collected from 10.5 h of observations using MeerKAT’s L-band receivers over six nights covering the 11 h field of WiggleZ, in the frequency range 1015–973 MHz (0.400
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    MeerKLASS L-band deep-field intensity maps: entering the H I dominated regime
    (Oxford University Press, 2025) Bull, Philip; Camera, Stefano; Engelbrecht, Brandon; Fonseca, José; Irfan, Melis; Li, Yichao; Pourtsidou, Alkistis; Santos, Mario; Spinelli, Marta; Wang, Jingying; Witzemann, Amadeus
    We present results from MeerKAT single-dish HI intensity maps, the final observations to be performed in L-band in the MeerKAT Large Area Synoptic Survey (MeerKLASS) campaign. The observations represent the deepest single-dish HI intensity maps to date, produced from 41 repeated scans over 236 deg2, providing 62 h of observational data for each of the 64 dishes before flagging. By introducing an iterative self-calibration process, the estimated thermal noise of the reconstructed maps is limited to ∼ 1.21 mK (1.2 × the theoretical noise level). This thermal noise will be subdominant relative to the HI fluctuations on large scales (k ≲ 0.15 h Mpc−1), which demands upgrades to power spectrum analysis techniques, particularly for covariance estimation. In this work, we present the improved MeerKLASS analysis pipeline, validating it on both a suite of mock simulations and a small sample of overlapping spectroscopic galaxies from the Galaxy And Mass Assembly (GAMA) survey. Despite only overlapping with ∼ 25 per cent of the MeerKLASS deep field, and a conservative approach to covariance estimation, we still obtain a > 4 σ detection of the cross-power spectrum between the intensity maps and the 2269 galaxies at the narrow redshift range 0.39 < z < 0.46. We briefly discuss the HI autopower spectrum from these data, the detection of which will be the focus of follow-up work. For the first time with MeerKAT single-dish intensity maps, we also present evidence of HI emission from stacking the maps onto the positions of the GAMA galaxies.