Ultra diffuse galaxies in the MATLAS low-to-moderate density fields
  Recent advances in deep dedicated imaging surveys over the past decade have
uncovered a surprisingly large number of extremely faint low surface brightness
galaxies with large physical sizes called ultra diffuse galaxies (UDGs) in
clusters and, more recently, in lower density environments. As part of the
MATLAS survey, a deep imaging large program at the Canada-France-Hawaii
Telescope (CFHT), our team has identified 2210 dwarf galaxies, 59 (~3%) of
which qualify as UDGs. Averaging over the survey area, we find ~0.4 UDG per
square degree. They are found in a range of low to moderate density
environments, although 61% of the sample fall within the virial radii of
groups. Based on a detailed analysis of their photometric and structural
properties, we find that the MATLAS UDGs do not show significant differences
from the traditional dwarfs, except from the predefined size and surface
brightness cut. Their median color is as red as the one measured in galaxy
clusters, albeit with a narrower color range. The majority of the UDGs are
visually classified as dwarf ellipticals with log stellar masses of ~6.5-8.7.
The fraction of nucleated UDGs (~34%) is roughly the same as the nucleated
fraction of the traditional dwarfs. Only five (~8%) UDGs show signs of tidal
disruption and only two are tidal dwarf galaxy candidates. A study of globular
cluster (GC) candidates selected in the CFHT images finds no evidence of a
higher GC specific frequency S_N for UDGs than for classical dwarfs, contrary
to what is found in most clusters. The UDG halo-to-stellar mass ratio
distribution, as estimated from the GC counts, peaks at roughly the same value
as for the traditional dwarfs, but spans the smaller range of ~10-2000. We
interpret these results to mean that the large majority of the field-to-group
UDGs do not have a different formation scenario than traditional dwarfs.
