2024MNRAS.534..202P

We present a deep H I survey at L band conducted with the Five-hundred-metre Aperture Spherical radio Telescope (FAST) over the COSMOS field. This survey is strategically designed to overlap with the MIGHTEE COSMOS field, aiming to combine the sensitivity of the FAST and high-resolution of the MeerKAT. We observed the field with FAST for approximately 11 hours covering ${\sim} 2$ square degrees, and reduced the raw data to H I spectral cubes over the frequency range 1310-1420 MHz. The FAST-H I data reach a median 3$\sigma$ column density of $N_{\rm {H\,{{\small I}}}} \sim 2\times 10^{17}$ cm$^{-2}$ over a ${\sim} 5\, {\rm km}\, {\rm s}^{-1}$ channel width, allowing for studies of the distribution of H I gas in various environments, such as in galaxies, the Circum-Galactic Medium (CGM) and Intergalactic Medium (IGM). We visually searched the spectral cubes for H I sources, and found a total of 80 H I detections, of which 56 have been cross-matched with the MIGHTEE-H I catalogue. With the cross-matched sources, we compare their H I masses and find that the total H I mass fraction in the IGM and CGM surrounding the galaxy pairs is statistically higher than the H I fraction surrounding the isolated galaxies by a difference of ${\sim} 13\pm 4$ per cent, indicating that the CGM and IGM associated with interacting systems are richer in neutral hydrogen compared to those around isolated galaxies in the local Universe. We also describe several FAST-MeerKAT synergy projects, highlighting the full potential of exploiting both single-dish and interferometric observations to study the distribution and evolution of the diffuse H I gas.