The detection of a massive chain of dark HI clouds in the GAMA G23 Field
  We report on the detection of a large, extended HI cloud complex in the GAMA
G23 field, located at a redshift of $z\,\sim\,0.03$, observed as part of the
MeerHOGS campaign (a pilot survey to explore the mosaicing capabilities of
MeerKAT). The cloud complex, with a total mass of $10^{10.0}\,M_\odot$, lies in
proximity to a large galaxy group with $M_\mathrm{dyn}\sim10^{13.5}\,M_\odot$.
We identify seven HI peak concentrations, interconnected as a tenuous 'chain'
structure, extending $\sim 400\,\mathrm{kpc}$ from east-to-west, with the
largest (central) concentration containing $10{^{9.7}}\,M_\odot$ in HI gas
distributed across $50\,\mathrm{kpc}$. The main source is not detected in
ultra-violet, optical or infrared imaging. The implied gas mass-to-light
($M_\mathrm{HI}$/$L_\mathrm{r}$) is extreme ($>$1000) even in comparison to
other 'dark clouds'. The complex has very little kinematic structure
($110\,\mathrm{km}\,\mathrm{s}^{-1}$), making it difficult to identify cloud
rotation. Assuming pressure support, the total mass of the central
concentration is $>10^{10.2}\,M_\odot$, while a lower limit to the dynamical
mass in the case of full rotational support is $10^{10.4}\,M_\odot$. If the
central concentration is a stable structure, it has to contain some amount of
unseen matter, but potentially less than is observed for a typical galaxy. It
is, however, not clear whether the structure has any gravitationally stable
concentrations. We report a faint UV--optical--infrared source in proximity to
one of the smaller concentrations in the gas complex, leading to a possible
stellar association. The system nature and origins is enigmatic, potentially
being the result of an interaction with or within the galaxy group it appears
to be associated with.
