Figure: Stellar Tidal Stream in the Halo of Messier 63 (NGC 5055)

The figure shows a very faint, giant arc-loop feature in the halo of the nearby spiral galaxy Messier 63 (NGC 5055). This feature is the stellar stream of a disrupted dwarf satellite galaxy.

This faint feature was first detected in early photographic studies by van der Kruit in 1979 but it was unknown if the faint structure was associated with Messier 63 (NGC 5055) or interveening Milky Way galactic cirrus like that contaminating our view of Messier 81 (NGC 3031). Our study realized it was the result of a minor merger between the large spiral and a much smaller satellite galaxy companion. Our initial observations were obtained from deep wide field images exposed through a modest telescope with an aperture of only 0.16 meters (106 milimeters).

Its presence has been confirmed in deep images taken with the 0.5 meter telescope of the BlackBird Remote Observatory (seen here) and the 0.8 meter telescope of the McDonald Observatory. This arc-like structure around the disk of the galaxy has a very low surface brightness and extends 14.0' (29 kpc projected) from its center with a projected width of 1.6' (3.3 kpc). The stream's morphology is consistent with a giant "great-circle" type stellar stream that originated from the accretion of a dwarf satellite sometime within the last 5 billion years. The progenitor satellite's current position and final fate are unknown, although the color of the stream's stars are consistent with dwarfs in the Local Group.

Credit: T. S. Chonis (Texas Univ.), D. Martínez-Delgado (MPIA, IAC), R. J. GaBany (Blackbird), Ray Gralak (New Mexico Skies), Gary J. Hill (McDonald Obs), I. Trujillo (IAC), S. R. Majewski (Virginia Univ.)

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