Suppressed star training in the early universe

Massive clusters of galaxies, with more than 100 Milky Way galaxies, have been detected from cosmic epochs as early as three billion years after the big bang. Their ongoing star training makes them bright enough to be detected at these distances. These kinds of clusters have been predicted by simulations of cosmological evolution but their properties are very uncertain. Astronomers piecing together the evolution of stars in the universe are particularly interested in these clusters because of their abundance of stars and activity.

Star formation in galaxies is by no means a steady process. Not only can it be used in a collision with a neighboring galaxy, but the opposite can occur. Star training can be self-limiting because its massive young stars produce wind and supernovae that can blow up the natal molecular clouds and disable future star training. Combined with the disruption caused by an active nuclear supermassive black hole, this disruptive process is called quenching and is thought to be able to bring star formation to a halt. Whether or not this occurs in the early universe, and when and how it proceeds, is a key area of ​​comic research.

CfA Astronomers Matt Ashby and Esra Bulbul are members of the South Pole Telescope (SPT) team that discovered massive galaxy clusters in the early universe. They recently completed a follow-up study of star formation and stellar populations in most remote clusters found in the SPT surveys. Using the IRAC camera on the Spitzer Space Telescope along with the Hubble Space Telescope Wide Field camera, they are estimated to be about 4.5 billion years old after the big bang, when galaxies in general were particularly active in producing new stars. Clusters of this size are exceedingly rare at these distances, and this is the first such study ever done.

Using the infrared colors of the galaxies in the selected SPT clusters, the scientists were able to characterize the stars and the star training activity. The scientists found that, curiously, during this epoch the massive clusters tend to host a mixture of galaxy with quiescent galaxies being quite common. Apparently in these quiescent cluster members the quenching of star formation has already occurred. The astronomers conclude that star formation can be effectively suppressed in the central regions of the most massive clusters even in these early cosmic epochs when the most intense star formation is occurring.