Star formation in galaxies appears to be highly regulated by the flow of gas into and out of galaxies. We still haven’t pinned down the specifics of these flows, but we can learn a lot about them by studying galaxies during “cosmic noon”, when star formation rates across the universe were at their highest.
Star formation rates versus redshift (lower axis) and lookback time (upper axis). The star formation rates were determined from infrared and ultraviolet observations. The peak around redshifts 2 and 3, or “cosmic noon”, is evident. [Madau & Dickinson, 2014]
The Ins and Outs at Cosmic Noon
“Cosmic noon” corresponds to redshifts of z = 2–3, when the universe was roughly between 2 to 3 billion years old (coincidentally). Over this relatively short period, galaxies formed about half of their current stellar mass. This makes cosmic noon an ideal time to examine mechanisms of star formation.
Stars form from gas, and gas is constantly flowing in and out of galaxies. Specifically, gas flows between the intergalactic and the interstellar mediums, passing through the circumgalactic medium (CGM) as it does. So, the CGM is a record-keeper of what sort of gas has flowed in and out of ...