2022ApJ...926..167J

We report on the detection of a large, extended H I cloud complex in the Galaxy and Mass Survey G23 field, located at a redshift of z ∼ 0.03, observed as part of the MeerKAT Habitat of Galaxies Survey campaign (a pilot survey to explore the mosaicing capabilities of the MeerKAT telescope). The cloud complex, with a total mass of 10^10.0 M _☉, lies in proximity to a large galaxy group with M _dyn ∼ 10^13.5 M _☉. We identify seven H I peak concentrations, interconnected as a tenuous chain structure, extending ∼400 kpc from east to west, with the largest (central) concentration containing 10^9.7 M _☉ in H I gas distributed across 50 kpc. The main source is not detected in ultraviolet, optical, or infrared imaging. The implied gas mass-to-light ratio (M _H I_/L r_) is extreme (>1000) even in comparison to other dark clouds. The complex has very little kinematic structure (110 km s^–1), making it difficult to identify cloud rotation. Assuming pressure support, the total mass of the central concentration is > 10^10.2 M _☉, while a lower limit to the dynamical mass in the case of full rotational support is 10^10.4 M _☉. 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.