The early universe is a fascinating and mysterious place, filled with puzzles that challenge our understanding of the cosmos. One such puzzle concerns the massive quiescents (MQs) - galaxies that formed soon after the Big Bang but stopped creating new stars just a billion years or so after they formed. This is particularly intriguing when compared to our own Milky Way, which is over 13 billion years old and is still producing stars, albeit at a slower rate. So, what happens to these MQs that strangles their star formation?
Researchers at the Institute of Astronomy, Geophysics, and Atmospheric Sciences at the University of São Paulo, along with collaborators from Denmark, the Netherlands, and the UK, think they have determined the reason for this premature quenching. Their work, published in Astronomy and Astrophysics, suggests that these galaxies may have undergone a phase as dusty star-forming galaxies (DSFGs) before becoming quiescent. This is an important finding, as it could help us understand the processes that drive the fuelling and quenching of star formation in the early universe.
DSFGs are the opposite of MQs - they are prolific star-formers, producing up to 500 solar masses of stars per year, compared to the Milky Way's one solar mass per year. However, DSFGs are cloaked in thick dust that blocks optical light, making them difficult to study. Researchers have developed models to explain both MQs and DSFGs, but there is a persistent tension in these models. The new research, which used the Millennium simulation, produced a better match between the observed numbers of both MQs and DSFGs, suggesting that the physical mechanisms required for efficient dust-obscured starbursts may be at odds with those needed for rapid quenching and MQ formation.
The key finding of the research is that major galaxy mergers can simultaneously boost both supernova (SN) and active galactic nuclei (AGN) feedback, which is the main driver of the growth of supermassive black holes. These mergers can create starbursts, which show up as infrared and sub-millimetre DSFGs, but then the SN and AGN feedback quench star formation. The researchers found that most MQs first went through a phase as DSFGs, and the most massive MQs were the brightest during their DSFG phase.
While the model doesn't perfectly match observations, it provides a valuable insight into the processes that drive galaxy evolution. The researchers hope that their findings will feed into more observations and modelling in the future, helping to refine our understanding of the cosmos. In my opinion, this is an exciting development in astronomy, and it highlights the importance of continued research and exploration in the field.
