A Deep Look at Neutral Hydrogen: Exploring the Outer Disks of Galaxies with MHONGOOSE and MeerKAT

The MHONGOOSE survey obtained ultra-deep 21-cm neutral hydrogen (HI) observations with the MeerKAT radio telescope to map the distribution and kinematics of low-column-density gas in and around 30 nearby star-forming spiral and dwarf galaxies. MHONGOOSE routinely reaches its target HI column-density sensitivity of a few times 10^{17} atoms cm^{-2}, two orders of magnitude below the typical column densities found in galaxy HI disks.

These extremely deep resolved HI observations of nearby galaxies show that the outskirts of disk galaxies are complex and dynamic environments, with many potential accretion and interaction features visible in HI that have only now become detectable thanks to MeerKAT's excellent column-density sensitivity.

MHONGOOSE provides unique constraints on the role of cold gas in replenishing the gas reservoirs of nearby galaxies, as shown by a first comparison of the MHONGOOSE observations with simulated HI maps from recent cosmological simulations, revealing marked differences in both morphology and kinematics and suggesting that cold-gas accretion may proceed more gently than predicted. I also discuss the unexpected variety in the shapes of the outer radial HI profiles and the relative importance of photoionisation and environment in shaping the outer HI disks.

The sensitive MHONGOOSE observations point the way towards a better understanding of the role of gas accretion in galaxy evolution in the nearby Universe and highlight opportunities for future HI surveys with the upcoming SKA-MID telescope.


Speaker: 
Erwin de Blok (ASTRON, Netherlands)
Place: 
KIAA-auditorium
Host: 
Jing Wang
Time: 
Thursday, July 30, 2026 - 3:00PM to Thursday, July 30, 2026 - 4:00PM
Biography: 
Prof. de Blok’s research focuses on the structure, dynamics, and evolution of galaxies, with a particular emphasis on the role of neutral hydrogen gas. He is especially known for his work on low surface brightness galaxies and the dark matter distribution in disk galaxies. He serves as the Principal Investigator of the MHONGOOSE survey, a MeerKAT Large Survey Program which uses the SKA precursor telescope MeerKAT to make extremely deep observations of neutral hydrogen in nearby galaxies. This work is supported by a 2.5 million euro ERC Advanced Grant "MeerGas". Prof de Blok works at the Netherlands Institute for Radio Astronomy. In addition, in 2021, Prof. de Blok was appointed Honorary Professor in the Structure and Evolution of Nearby Galaxies at the Kapteyn Astronomical Institute of the University of Groningen. He is also affiliated with the University of Cape Town as an Honorary Professor. He has contributed significantly to the development of MeerKAT and the Square Kilometre Array (SKA). Prof. de Blok has authored over 200 papers that have received over 28,000 citations.