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