MHONGOOSE survey takes its final observation

BY PROF. ERWIN DE BLOK (ASTRON)

In December, the final MeerKAT observation of the MHONGOOSE survey was taken. MHONGOOSE, or MeerKAT HI Observations of Nearby Galactic Objects – Observing Southern Emitters, is an ultra-deep HI survey of 30 nearby galaxies, mapping the cool gas in these galaxies down to column densities two orders of magnitude deeper than previous observations.

Each of the galaxies was observed for 55 hours, making this the largest and deepest HI nearby galaxy survey until SKA-Mid comes online in the coming years.

The key science goals of MHONGOOSE, which began in 2020, are to search for signs of gas accretion in the outer parts of these galaxies, as well as to study the relation between gas and star formation in the inner discs.

While the reduction and analysis of the MHONGOOSE data are still in full swing, some intriguing results have already started to come out of the survey.

These include the discovery of an extremely low-mass dwarf galaxy near NGC 1566, a galaxy about 65 million light years away – these kind of galaxies could so far only be studied in the Local Group of the Milky Way and its neighbours. A low-column-density gas disc was found around galaxy NGC 5068, but without signs of interactions, active star formation or inflows, it is not clear what the origin of this component is.

Studies of stacked spectra of the MHONGOOSE data indicate a surprising absence of very low-column-density gas around the sample galaxies, in apparent contradiction to expectations from cosmological simulations. These are just some of the many results that have come, and will continue to come, out of the survey, opening up new queries and investigations. For more information visit the survey website.