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 HI envelope around this system has been detected.

The total HI gas mass of the NGC 3395/3396 system is estimated to be 7.8 x 109 M.

This value is 2.7 times more than that reported based on the VLA interferometric maps.

Previous observations found a large HI 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 HI 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 on the south of the system have also been detected.

We discuss the origins of these extra gas and possible tidal interactions between these galaxies.

NGC 3395/3396's most prominent tidal feature, 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 NGC 3396 which happened 500 Myr ago.

Our study shows that high-sensitivity HI observations are important in revealing low column density gas, which is crucial to a deeper understanding of this interacting system.