Browsing by Author "Li, Yichao"

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    FAST drift scan survey for HI Intensity mapping: simulation of Bayesian-stacking-based HI mass function estimation
    (Institute of Physics, 2025) Hu, Wenkai; Wang, Jiaxin; Li, Yichao
    This study investigates the estimation of the neutral hydrogen (Hi) mass function (HiMF) using a Bayesian stacking approach with simulated data for the Five-hundred-meter Aperture Spherical radio Telescope (FAST) Hi intensity mapping (HiIM) drift-scan surveys. Using data from the IllustrisTNG simulation, we construct Hi sky cubes at redshift 𝑧 ∌ 0.1 and the corresponding optical galaxy catalogs, simulating FAST observations under various survey strategies, including pilot, deep-field, and ultradeep-field surveys. The HiMF is measured for distinct galaxy populations– classified by optical properties into red, blue, and bluer galaxies– and injected with systematic effects such as observational noise and flux confusion caused by the FAST beam. The results show that Bayesian stacking significantly enhances HiMF measurements. For red and blue galaxies, the HiMF can be well constrained with pilot surveys, while deeper surveys are required for the bluer galaxy population. Our analysis also reveals that sample variance dominates over observational noise, emphasizing the importance of wide-field surveys to improve constraints. Furthermore, flux confusion shifts the HiMF toward higher masses, which we address using a transfer function for correction. Finally, we explore the effects of intrinsic sample incompleteness and propose a framework to quantify its impact. This work lays the groundwork for future HiMF studies with FAST HiIM, addressing key challenges and enabling robust analyses of Hi content across galaxy populations.
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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 â‰Č 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.