Discovery of Extra-Planar HI Clouds and a HI Tail in the M101 Galaxy Group with FAST

TL;DR

This study uses FAST to reveal extended HI features around M101, including new clouds and a tail, indicating minor interactions with nearby dwarf galaxies and providing insights into galaxy evolution.

Contribution

First high-sensitivity HI observations of M101 with FAST uncover new extra-planar clouds and a tail, suggesting recent minor interactions with dwarf companions.

Findings

Detection of three new HI clouds with no optical counterparts.

Identification of an HI tail indicating galaxy interaction.

Extended asymmetric HI disk around M101.

Abstract

We present a new high-sensitivity HI observation toward nearby spiral galaxy M101 and its adjacent 2$^{\circ}\times$ 2$^{\circ}$ region using the Five-hundred-meter Aperture Spherical radio Telescope (FAST). From the observation, we detect a more extended and asymmetric HI disk around M101. While the HI velocity field within the M101's optical disk region is regular, indicating that the relatively strong disturbance occurs in its outer disk. Moreover, we identify three new HI clouds located on the southern edge of the M101's HI disk. The masses of the three HI clouds are 1.3$\times$10$^{7}$ $M_{\odot}$, 2.4$\times$10$^{7}$ $M_{\odot}$, and 2.0$\times$10$^{7}$ $M_{\odot}$, respectively. The HI clouds similar to dwarf companion NGC 5477 rotate with the HI disk of M101. Unlike the NGC 5477, they have no optical counterparts. Furthermore, we detect a new HI tail in the extended HI disk of M101. The HI tail detected gives a reliable evidence for M101 interaction with the dwarf companion NGC 5474. We argue that the extra-planar gas (three HI clouds) and the HI tail detected in the M101's disk may origin from a minor interaction with NGC 5474.