Free Astronomy Magazine May-June 2021

25 MAY-JUNE 2021 ASTRO PUBLISHING thus ending galaxies’ ability to make new stars. However, the new study published in Nature Astronomy sug- gests that galactic mergers can also be responsible for ejecting star- forming fuel into space. “Our study suggests that gas ejec- tions can be produced by mergers and that winds and tidal tails can ap- pear very similar,” says study co-au- thor Emanuele Daddi of CEA-Saclay. Because of this, some of the teams that previously identified winds from distant galaxies could in fact have been observing tidal tails eject- ing gas from them. “This might lead us to revise our understanding of how galaxies ‘die’,” Daddi adds. Puglisi agrees about the significance of the team’s finding, saying: “I was thrilled to discover such an excep- tional galaxy! I was eager to learn more about this weird object be- cause I was convinced that there was some important lesson to be learned about how distant galaxies evolve.” This surprising discovery was made by chance, while the team were in- specting a survey of galaxies made with ALMA, designed to study the properties of cold gas in more than 100 far-away galaxies. ID2299 had been observed by ALMA for only a few minutes, but the powerful ob- servatory, located in northern Chile, allowed the team to collect enough data to detect the galaxy and its ejection tail. “ALMA has shed new light on the mechanisms that can halt the formation of stars in distant galaxies. Witnessing such a massive disruption event adds an important piece to the complex puzzle of galaxy evolution,” says Chiara Cir- costa, a researcher at the University College London, UK, who also con- tributed to the research. In the future, the team could use ALMA to make higher-resolution and deeper observations of this galaxy, enabling them to better un- derstand the dynamics of the ejected gas. Observations with the future ESO’s Extremely Large Tele- scope could allow the team to ex- plore the connections between the stars and gas in ID2299, shedding new light on how galaxies evolve. ! T his artist’s impression of ID2299 shows the galaxy, the product of a galactic collision, and some of its gas being ejected by a “tidal tail” as a result of the merger. New observations made with ALMA, in which ESO is a partner, have captured the earliest stages of this ejection, before the gas reached the very large scales depicted in this artist’s impression. [ESO/M. Kornmesser]