By Enrico Di Teodoro
[email protected]
The access to ESO facilities is opening up great opportunities of carrying out new exciting research for the astronomy community in Australia. In particular, I have used this opportunity to study local galactic winds.
Galactic outflows are a fascinating process at play in the evolution of galaxies. Star formation and black holes can inject huge amounts of energy in the interstellar medium of galaxies and expel gas in the form of a wind. These phenomena are believed to have an important role in the evolution of the host galaxy, as they remove the material needed to form new stars. The closest places in the Universe where we can study these processes in detail are our Galaxy, the Milky Way, and its satellites, the Magellanic Clouds. The synergy between Australia’s newest radio telescope, the Australian SKA Pathfinder (ASKAP), and a modern sub-millimeter ESO instrument, the Atacama Pathfinder EXperiment (APEX), are allowing us to investigate the nature of cold gas living within local galactic winds with unprecedented accuracy.
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.
