© Erwin de Blok (ASTRON/UCT/RuG)
With these deepest resolved HI observations of nearby galaxies to date, we want to detect cold gas accretion. This is the process by which galaxies replenish their gas reservoirs from the cosmic web, enabling them to continue forming stars throughout cosmic time.
The survey is now 90% complete, and is routinely reaching its target HI column density sensitivity of a few times 10^17 atoms cm-2, two orders of magnitude lower than the typical values found in galaxy HI disks.
Our full-depth data show that the outskirts of our galaxies are complex and dynamic environments, with many potential accretion and interaction features that only now become visible due to the excellent column density sensitivity. We detect a significant number of uncatalogued low-mass dwarf galaxies, which enable us to do the kind of science in environments at tens of Mpc distance that was so far only possible in the Local Group.
A first comparison of the MHONGOOSE galaxies with simulated HI data extracted from recent cosmological simulations shows a marked difference in kinematics and morphology, indicating that cold gas accretion is not happening in the form simulations predict.
This discrepancy between observations and simulations is a challenge but also points the way to a better understanding of the role of gas accretion in galaxy evolution and identifies opportunities for new HI surveys with the upcoming SKA-MID telescope.