FAST observations of neutral hydrogen in the interacting galaxies NGC 3395/3396

We report on high-sensitivity neutral hydrogen observations toward the gas-rich interacting galaxies NGC 3395/3396 with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). Compared to previous observations carried out by the Very Large Array (VLA) and the Westerbork Synthesis Radio Telescope (WSRT), a more extended H I envelope around this system has been detected. The total H I gas mass of the NGC 3395/3396 system is estimated to be 7.8 × 10⁹ M$_\odot$. This value is 2.7 times more than that reported based on the VLA interferometric maps. Previous observations found a large H I tail extending to the south-west and a minor tail emerging from the north of this peculiar galaxy pair. Based on the high-sensitivity observations of FAST, an extended H I plume to the north-west and a gas plume to the north-east have been detected for the first time. Neutral hydrogen of the two smaller galaxies IC 2604 and IC 2608 in the south of the system have also been detected. We discuss the origins of these extra gas and possible tidal interactions between these galaxies. The most prominent tidal feature of NGC 3395/3396, the south-west tail combined with the new detected north-west plume, behaves like a large ring. We suggest the ring might be formed by the previous fly-by interaction between NGC 3395 and 3396, which happened 500 Myr ago. Our study shows that high-sensitivity H I observations are important in revealing low column density gas, which is crucial to a deeper understanding of this interacting system.