Tracing satellite planes in the Sculptor group: I. Discovery of three
  faint dwarf galaxies around NGC 253
  In the last years, a new generation of large-scale imaging surveys have
probed wide field regions around some nearby galaxies at unprecedented low
surface brightness regime (~28.0-29.0 mag arcsec^-2). This offers a chance of
discovering very faint dwarf satellites by means of visual inspection of these
public deep images. We report the first results of a systematic survey of faint
dwarf spheroidal galaxies in the vicinity of the bright late-type spiral NGC
253 galaxy by means of a visual inspection of the images taken by the Dark
Energy Survey. Three new dwarf galaxies have been discovered in the vicinity of
the brightest member of the Sculptor filament, the late-type spiral NGC 253.
Assuming they are companions of NGC 253, their total absolute V-magnitudes fall
in the -7 to -9 mag range, which is typical for dwarf satellites in the local
Universe. The central surface brightness tend to be extremely low for all the
discovered dwarfs and fall roughly in the range of 25-26 mag arcsec^-2 in
g-band. Using known data on distances and velocities of galaxies, we estimate
the total virial mass of the NGC 253 group to be 8 x 10^11 Mo, which gives the
virial radius R_200 = 186 kpc and the turn-around radius of 706 kpc. We also
discuss the possible existence of a spatially flattened and velocity-correlated
satellite system around NGC 253. This large-scale structure is orientated
almost edge-on to line of sight. The possible plane of satellites is only 31
kpc thick with the minor-to-major axis ratio of 0.14. Four out of five galaxies
with measured velocities follow a common velocity trend similar to those
observed in the planes of satellites around the Andromeda and Centaurus A
galaxies. However, the small number of galaxies with known velocities prevents
to reach a definitive conclusion about the formation scenario of the structure
and its possible relation to the surrounding cosmic web.
