J2000.0 RA 13h 15m 49.3s Dec +42° 01′ 45″

Messier 63 (NGC 5055) is a spiral galaxy in Canes Venatici, 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 is in the halo of the spiral galaxy. This feature is the stellar stream of a disrupted dwarf satellite galaxy and it was first detected in early photographic studies by Van der Kruit in 1979.

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)

[https://arxiv.org/abs/1207.2115]

A: Standard version L-g,r,z filters

B: Inverted version with color insert, corresponding with the disk of the galaxy. As can be seen from this elaboration, the stellar streams system is much more articulated than simple nuanced flows. The sensitivity of the ZTF camera is impressive, capable of showing these weak structures already in a single frame in just 30 seconds, ie the standard exposure used by the survey.

C: Public version processed, however without loss of scientific content. Note how the main loop appears to consist of old stars. This means that the disrupted galaxy was supposed a dwarf galaxy. Note also the dwarf galaxy which appears straight and curved (to the right). The analysis of stellar currents allows to have a picture of the scenario in the halo of dark matter that envelops the galaxy. Probably, some clear deviations that can be seen, are attributable to local thickenings of dark matter, that is to say to satellites without stars. This can be ascertained by n-body simulation.