The radio astronomy group at the Australian National University (Canberra), led by Prof. Naomi McClure-Griffiths, recently used ASKAP to observe the atomic hydrogen (HI) content of the smaller of the Milky Way's companions, the Small Magellanic Clouds (SMC). The SMC has several regions of intense star formation (red regions in Figure 1 above), hence it is a great laboratory to understand the connection between stellar feedback and galactic winds. The new HI data, which has an exquisite resolution of about 10 pc, revealed for the first time several filaments (Figure 2, left) and shells of atomic gas at a temperature of about 8000 K that are escaping from the galaxy (McClure-Griffiths et al. 2018). Two of these HI structures are shown in Figure 1 in blue. To assess whether these clouds carry also cold molecular gas (10-100 K), we followed them up with APEX observations. The APEX antenna, which is available to Australian researchers thanks to the strategic partnership with ESO, was the ideal instrument as it is one of the very few telescopes in the world that can quickly and deeply map molecules in large regions of the sky.
Our new APEX data showed that large amounts of molecular gas are present in the form of dense, compact clumps (Figure 2, right). This was the first evidence of a molecular outflow in a gas-rich dwarf galaxy (Di Teodoro et al. 2019). We believe that this cold gas is being pushed out and accelerated by the hot flow produced by supernova explosions and stellar winds in the region enclosed by the red box in Figure 1. The combined ASKAP and APEX data led us to estimate that the SMC is losing up to 1.5 solar masses of cold gas (atomic plus molecular) every year. This outflow could have an important impact in the future life of the SMC, because it is removing a significant fraction of the cold gas reservoir from which new stars are formed. We calculated that, because of the outflow, the star formation process on the SMC may be quenched within the next billion years.