Two articles, one published in “The Astrophysical Journal Letters” and one in “The Astrophysical Journal”, report the results of studies on ancient quenching galaxies, which means that they strongly reduced or even finished their star-formation activity. Two teams of researchers with many of them in common used data collected with various telescopes to study these galaxies and establish that we see the oldest as it was about 1.5 billion years after the Big Bang. These studies offer new information to improve galaxy formation models.
Star formation pace is one of the most important elements in the study of galaxies to understand which factors can increase or decrease or even stop that pace. It’s related to the amount of hydrogen available in a galaxy but there are also conditions more or less suitable for triggering the formation of new stars and in some cases a galaxy can become quenching. Understanding exactly the mechanisms that lead to such a situation is still the subject of research.
In recent years, astronomers found galaxies that had become quenching after a few billion years. In the research reported by the two new articles, three galaxies were selected from particularly distant ones, which appear to us as they were less than two billion years after the Big Bang, and known as quenching. The distances were calculated using the MOSFIRE spectrograph at the Keck Observatory, Hawaii, and the X-shooter instrument mounted on one of the telescopes of the VLT (Very Large Telescope) in Chile.
Observations confirm that we see the farthest quenching galaxy as it was about 1.5 billion years after the Big Bang. It’s a very massive galaxy, with over a trillion stars, but their formation was reduced significantly and is now, both in it and in the other two studied galaxies, more than ten times less than in galaxies with similar masses and ages. Anna Gallazzi of the Italian National Institute of Astrophysics, Arcetri, co-author of the two articles, explained that she and her colleagues estimated that the three galaxies studied had a star formation phase that occurred a few hundred million years before their current state. At the time, that peak was probably thousands of solar masses per year, lasting a few tens of millions of years.
Francesco Valentino of the Niels Bohr Institute at the Danish University of Copenhagen, another of the authors of the two articles, added that the suppressed stellar activity tells us that a galaxy is dying but it’s precisely the type of galaxy that astronomers want to study in detail to understand why it became quenching. Astronomers think that massive galaxies are the first to die in the history of the universe and that contains the key to understanding why they become quenching. It’s not an easy search because telescopes allow to find galaxies in extreme situations but it’s difficult to find normal galaxies to understand the first phases in which they start becoming quenching.
The study of quenching galaxies is among the ones that can make progress when at last it will be possible to use the James Webb space telescope. At that point, interesting galaxies such as the ones examined in these studies may be subject to follow-up research to obtain much higher quality data. Maybe in the next few years it will be possible to really understand why certain galaxies die.
