New dwarfs around the curly spiral galaxy M 63

Abstract

We present a deep (50‐hr exposed) image of the nearby spiral galaxy M 63 (NGC 5055), taken with a 0.14‐m aperture telescope. The galaxy halo exhibits the known, very faint system of stellar streams extending across 110 kpc. We found five very low‐surface‐brightness dwarf galaxies around M 63. Assuming they are satellites of M 63, their median parameters are: absolute B‐magnitude −8.8 mag, linear diameter 1.3 kpc, surface brightness ∼27.8 mag/sq. arcsec, and linear projected separation 93 kpc. Based on four brighter satellites with measured radial velocities, we found the low orbital mass estimate of M 63 to be (5.1 ± 1.8)1011M⊙ on a scale of ∼216 kpc. The specific property of M 63 is its declining rotation curve. Taking into account the declining rotation curves of the M 63 and three nearby massive galaxies, NGC 2683, NGC 2903, and NGC 3521, we recognize their low mean orbital mass‐to‐K‐band luminosity ratio, (4.8 ± 1.1) M⊙/L⊙, which is only ∼1/6 of the corresponding ratio for the Milky Way and M 31.