Unipd-INAF Research: Measuring the "Fuel" of Galaxies from 4 billion Years Ago


Star formation occurs with the collapse of dense molecular hydrogen clouds when neutral hydrogen atoms bond together. A galaxy "consumes" neutral hydrogen and transforms it into molecular hydrogen that subsequently forms stars. To keep the active formation of new stars, a galaxy must have a continuous supply of atomic hydrogen.
But how is new neutral hydrogen generated within galaxies? The scientific literature suggests two options: the intergalactic medium diffuses an accretion of gas (cosmological accretion) or by the fusion of galaxies (galaxy merger). The only place where the relationships binding neutral hydrogen to other observable properties of galaxies have been observed are in the nearby Universe, corresponding to the last billion years

A team of researchers led by the PhD student, Francesco Sinigaglia, of the University of Padua Galileo Galilei Department of Physics and Astronomy in association with the National Institute of Astrophysics, published the article MIGHTEE-Hi: Evolution of Hi Scaling Relations of Star-forming Galaxies at z < 0.5 in The Astrophysical Journal Letters. Together with researchers from MIGHTEE (MeerKAT International GHz Tiered Extragalactic Exploration), the work measured the relationships that link the mass of atomic hydrogen to stellar mass and the rate of star formation in galaxies at a distance corresponding to 4 billion years ago for the first time.

Francesco Sinigaglia, first author of the study, explains, "At a distance never before reached, we have observed how the variation of atomic hydrogen changes as a function of the number of stars and the rate of star formation found in distant active galaxies (star-forming). Our results indicate that galaxies found at a distance of 4-5 billion years hold reserves of atomic hydrogen comparable to those of current galaxies, especially in the case of massive galaxies. Knowing that the formation of stars rapidly consumes atomic hydrogen, this data can be explained by hypothesizing that there is a mechanism that efficiently supplies galaxies with atomic hydrogen from outside. Using theoretical models, we aim to study which predominant hydrogen supply mechanism can explain the results obtained from these observations".