The M101 group complex: new dwarf galaxy candidates and spatial
  structure
  The fine details of the large-scale structure in the local universe provide
important empirical benchmarks for testing cosmological models of structure
formation. Dwarf galaxies are key object for such studies. Enlarge the sample
of known dwarf galaxies in the local universe. We performed a search for faint,
unresolved low-surface brightness dwarf galaxies in the M101 group complex,
including the region around the major spiral galaxies M101, M51, and M63 lying
at a distance 7.0, 8.6, and 9.0 Mpc, respectively. The new dwarf galaxy sample
can be used in a first step to test for significant substructure in the
2D-distribution and in a second step to study the spatial distribution of the
galaxy complex. Using filtering algorithms we surveyed 330 square degrees of
imaging data obtained from the Sloan Digital Sky Survey. The images were
visually inspected. The spatial distribution of known galaxies and candidates
was analyzed transforming the system into a M101 eigenframe, using the
geometrical alignment of the group. We discovered 15 new dwarf galaxies and
carried out surface photometry in the g and r bands. The similarity of the
photometric properties of these dwarfs to those of Local Group dwarfs suggest
membership to the M101 group complex. The sky distribution of the candidates
follows the thin planar structure outlined by the known members of the three
subgroups. The ~3Mpc long filamentary structure has a rms thickness of 67 kpc.
The planar structure of the embedded M101 subgroup is even thinner, with rms=46
kpc. The formation of this structure might be due to the expansion of the Local
Void to which it borders. Other implications are discussed as well. We show the
viability of SDSS data to extend the sample of dwarfs in the local universe and
test cosmological models on small scales.
