A Petal of the Sunflower: Photometry of the Stellar Tidal Stream in the
  Halo of Messier 63 (NGC 5055)
  We present surface photometry of a very faint, giant arc feature in the halo
of the nearby spiral galaxy NGC 5055 (M63) that is consistent with being a part
of a stellar stream resulting from the disruption of a dwarf satellite galaxy.
This faint feature was first detected in early photographic studies by van der
Kruit (1979); more recently by Mart\'inez-Delgado et al. (2010) and as
presented in this work, the loop has been realized to be the result of a recent
minor merger through evidence obtained by deep images taken with a telescope of
only 0.16 m aperture. The stellar stream is confirmed in additional images
taken with the 0.5 m of the BlackBird Remote Observatory and the 0.8 m of the
McDonald Observatory. This low surface brightness structure around the disk of
the galaxy extends ~29 kpc from its center, with a projected width of 3.3 kpc.
The stream's morphology is consistent with that of the visible part of a
"great-circle" stellar stream originating from the accretion of a ~10^8 M_sun
dwarf satellite in the last few Gyr. The progenitor satellite's current
position and fate are not conclusive from our data. The color of the stream's
stars is consistent with Local Group dwarfs and is similar to the outer regions
of M63's disk and stellar halo. We detect other low surface brightness
"plumes"; some of these may be extended spiral features related to the galaxy's
complex spiral structure and others may be tidal debris associated with the
disruption of the galaxy's outer stellar disk as a result of the accretion
event. We differentiate between features related to the tidal stream and faint,
blue features in the outskirts of the galaxy's disk previously detected by the
GALEX satellite. With its highly warped HI gaseous disk (~20 deg), M63
represents one of several examples of an isolated spiral galaxy with a warped
disk showing strong evidence of an ongoing minor merger.
