Revealing the Origin of Quiescent Galaxies at Cosmic Noon

In the nearby Universe astronomers have discovered that most galaxies are either actively forming new stars (appearing blue in color) or have ceased to form them (appearing red in color). In many ways, producing new stars is the most pronounced feature of galaxies in the local Universe, but there is no scientific consensus explaining why some galaxies cease forming stars.

Part of the problem is that the end of star formation occurred in most systems billions of years ago, where we currently lack the necessary observations to fully understand their physical properties. This team of researchers will address this issue by utilizing data from an upcoming survey of galaxies targeting early cosmic times. In so doing, they will constrain this crucial evolutionary stage in galaxies, helping to resolve one of the long-standing mysteries in all of astrophysics – why are there two types of galaxies?

The PI will establish a new program providing hands-on training in observational astronomy to undergraduate students of all majors. For this purpose, the PI will use the 24-in telescope on the campus of Florida International University, a Hispanic-Serving Institution.

This research team will utilize ‘VLT-MOONRISE’, an unprecedented study of about 500,000 galaxies observed with rest-frame optical spectroscopy at the peak epoch of galaxy formation (‘cosmic noon’: z = 1 – 2.5). This is a large (190-night) spectroscopic survey targeting early galaxies to be conducted on the Very Large Telescope in Chile over the next five years.

This research project will combine these transformative spectroscopic observations with state-of-the-art cosmological simulations and sophisticated machine learning tools to rigorously test theoretical models of galactic star formation quenching at cosmic noon. In particular, this project will: (1) Reveal the fundamental physics of galaxy quenching at cosmic noon: ‘fuel’ vs. ‘efficiency’; (2) Test the AGN feedback paradigm of massive galaxy quenching at cosmic noon; (3) Identify the triggers of massive galaxy quenching – e.g., mergers, starbursts vs.

AGN; (4) Determine the role of environment in quenching satellite galaxies at cosmic noon; and (5) Enable a census of star forming and quiescent galaxies across 10 billion years of cosmic history. Ultimately, this research will aim to reveal where and when in the Universe star formation is possible, explaining the fundamental bimodality in galaxy properties, which has remained elusive for decades.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.