Photometry of the Stellar Tidal Stream in the Halo of Messier 63

Abstract

We present surface photometry of a giant, low surface brightness stellar arc in the halo of the nearby spiral galaxy M63 (NGC 5055) that is consistent with being a part of a stellar stream resulting from the disruption of a dwarf satellite galaxy. Using the stream's great-circle morphology and its photometric properties, we estimate that the stream originates from the accretion of a 10^8 M_sun satellite in the last few Gyr. The B-R color of the stream's stars is consistent with Local Group dwarfs and is also similar to the outer regions of M63's disk and stellar halo within our measurement uncertainties. Additionally, we identify several other low surface brightness features that may be related to the galaxy's complex spiral structure or may be tidal debris associated with the disruption of the galaxy's outer stellar disk as a result of the accretion event. Using our deep, panoramic optical view of M63 with additional existing multiwavelength data, we describe the possible effects of such an accretion event in the larger picture of the parent galaxy.