File:M63 - A color density map (34626343140).jpg

Messier 63 Stellar Tidal Stream in the Halo Credit: Michele Trungadi / Giuseppe Donatiello (process)

J2000.0 RA 13h 15m 49.3s Dec +42° 01′ 45″ Messier 63 (NGC 5055) is a spiral galaxy in Canes Venatici, discovered by Pierre Méchain on June 14, 1779. M63 is part of the M51 Group, a group of galaxies that also includes M51 (the Whirlpool Galaxy). M63 is an active galaxy with a LINER nucleus. A very faint, giant arc-loop feature in the halo of the nearby spiral galaxy. 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 or interveening Milky Way galactic cirrus (IFN). This arc-like structure around the disk of the galaxy has a very low 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 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 (Taylor S. Chonis, David Martinez-Delgado et Alt. 2012)