Clustering and the Search for Dim and Dark Galaxies
  We re-investigate the question of whether there is a significant population
of Dim (Low Surface Brightness) and/or Dark Galaxies (DDGs). We argue that if
they are clustered with bright ones then a physical resolution of ~10 kpc. will
be needed to to distinguish their 21-cm. and QSO Absorption Line(QSOAL)
counterparts from their brighter neighbours, leading to a real possibility of
confusion. But until now such a resolution has not been available in this
context. New Very Large Array (VLA) observations reveal that the
identifications with bright optical objects claimed in previous single-dish
blind HI surveys are often unreliable. For instance 14/36 of our
high-resolution (5 arc sec, 13kpc.) sample have no optical counterparts in the
Digital Sky Survey. This suggests that DDGs might be commonplace after all, and
we go on to re-examine the main arguments that have been used against them.. We
find that the QSOAL argument founders on the aforementioned clustering while
deep CCD surveys have so far covered too small an area to set set strong
constraints on Low Surface Brightness Galaxies (LSBGs). A cosmos filled with
low surface brightness galaxies, dark galaxies and intergalactic gas clouds is
therefore possible.
