Exploring H <scp>i</scp> Galaxy Redshift Survey Strategies for the FAST Core Array Interferometry

Abstract We explore the feasibility of H i galaxy redshift surveys with the Five-hundred-meter Aperture Spherical Telescope (FAST) and its proposed Core Array interferometry. Using semi-analytical simulations, we compare the performance of the FAST single-dish and Core Array modes in drift scan (DS) and on-the-fly (OTF) observations across different redshifts. Our results show that the FAST single-dish mode enables significant H i detections at low redshifts ( z ≲ 0.35) but is limited at higher redshifts due to shot noise. The Core Array interferometry, with higher sensitivity and angular resolution, provides robust H i galaxy detections up to z ∼ 1, maintaining a sufficient number density for power spectrum measurements and BAO constraints. At low redshifts ( z ∼ 0.01–0.08), both configurations perform well, though cosmic variance dominates uncertainties. At higher redshifts ( z &gt; 0.35), the Core Array outperforms the single-dish mode, while increasing the survey area has little impact on single-dish observations due to shot noise limitations. The DS mode efficiently covers large sky areas but is constrained by Earth’s rotation, whereas the OTF mode allows more flexible deep-field surveys at the cost of operational overhead. Our findings highlight the importance of optimizing survey strategies to maximize FAST’s potential for H i cosmology. The Core Array is particularly well-suited for high-redshift H i galaxy surveys, enabling precise constraints on large-scale structure and dark energy.