Cosmic neighbours inhibit star formation, even in the early universe
The international University of California, Riverside-led SpARCS collaboration has discovered four of the most distant clusters of galaxies ever found, as they appeared when the universe was only 4 billion years old. Clusters are rare regions of the universe consisting of hundreds of galaxies containing trillions of stars, as well as hot gas and mysterious dark matter. Spectroscopic observations from the ground using the W. M. Keck Observatory in Hawaii and the Very Large Telescope in Chile confirmed the four candidates to be massive clusters. This sample is now providing the best measurement yet of when and how fast galaxy clusters stop forming stars in the early Universe.
|Colour images of the central regions of z > 1.35 SpARCS clusters. Cluster members are marked with white squares |
[Credit: SpARCS collaboration]
As anticipated, the team did indeed find that many more galaxies in the clusters had stopped forming stars compared to galaxies of the same mass in the field. Lead scientist Gillian Wilson, professor of physics and astronomy at UC Riverside, said, "Fascinatingly, however, the study found that the percentage of galaxies which had stopped forming stars in those young, distant clusters, was much lower than the percentage found in much older, nearby clusters. While it had been fully expected that the percentage of cluster galaxies which had stopped forming stars would increase as the universe aged, this latest work quantifies the effect." The paper concludes that about 30 percent of the galaxies which would normally be forming stars have been quenched in the distant clusters, compared to the much higher value of about 50 percent found in nearby clusters.
|Massive galaxy cluster MACS J0416 seen in X-rays (blue), visible light (red, green, and blue), and radio light (pink) |
While the current study does not answer the question of which process is primarily responsible, it is nonetheless hugely important because it provides the most accurate measurement yet of how much environmental quenching has occurred in the early universe. Moreover, the study provides an all-important early-universe benchmark by which to judge upcoming predictions from competing computational numerical simulations which make different assumptions about the relative importance of the many different environmental quenching processes which have been suggested, and the timescales upon which they operate.
Author: Mario De Leo Winkler. | Source: University of California - Riverside [August 24, 2016]