Dr. Daniel Tafoya

Daniel served as the ALMA Single-Dish CASA and Pipeline Subsystem Scientist at the East Asia ARC in Tokyo Japan from 2017-2019. From April 2019 he joined the Nordic ARC node as part of the observation support team at the Onsala Space Observatory in Sweden. One of his duties is supporting astronomers of the Nordic countries to reduce and analyse data obtained with interferometers, mainly ALMA. As a radio astronomer he is interested in anything that can be observed with a radio telescope, but he has focused his research on the study of the circumstellar material of evolved stars to understand how the interstellar medium is replenished with dust and gas.  

Dr. Gergö Popping

Gergö joined the ARC at ESO in September 2019. Within the ARC he is the coordinator of the European ARC nodes Network and the European member of the ALMA Helpdesk working group. His scientific interests include the properties of dust and gas in high-redshift galaxies, which he studies through a combination of simulations and ALMA observations. Gergö especially enjoys the day-to-day interaction with the many Network scientists that support the European community with their exciting ALMA science.

Distant colliding galaxy dying out as seen by ALMA

The physical processes responsible for the sudden termination of star formation in massive galaxies have not been clarified yet. Feedback-driven winds from star formation or active black holes are thought to be responsible for expelling the gas and quenching the growth of massive galaxies. However, direct observations of massive gas ejections, demonstrating the impact of such winds on the host galaxy star formation are still lacking.

Thanks to the sensitivity of ALMA, a galaxy in the act of quenching was observed (Puglisi et al. 2021). The galaxy ID2299, at a redshift of z=1.4, displays a prominent broad component in the CO(2-1) spectrum (Panel a in Figure), a proxy for the molecular gas reservoir. The spectral analysis suggests that 46 +- 13 % of the molecular gas is being ejected from the galaxy and the galaxy will stop forming stars in a few million years. This was a serendipitous discovery since the galaxy ID2299 was observed as part of an ALMA survey, designed to study the properties of the molecular gas in more than 100 galaxies at cosmic noon. Ancillary ALMA observations of higher-J CO/[CI] transitions (Panels b,d,e in Figure) were essential to study the physical properties of the gas and obtain clues on the mechanism causing this ejection, the major merger between two massive galaxies.

The discovery of this massive molecular gas ejection provides important indications on how galaxies die, and shows that mergers have a crucial role in the evolution of galaxies by expelling large quantities of gas from galaxies, shutting down star formation and affecting galaxy growth.