W.M. Keck Observatory | 2016 Aug 24
[img3="Color images of the central regions of z > 1.35 SpARCS clusters. Cluster members are marked with white squares. Credit: JB Nantais, et al"]http://www.keckobservatory.org/images/m ... 00_797.jpg[/img3][hr][/hr]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 four 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 W. M. Keck Observatory on Maunakea, 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.
“We looked at how the properties of galaxies in these clusters differed from galaxies found in more typical environments with fewer close neighbors,” said lead author Julie Nantais, an assistant professor at the Andres Bello University in Chile. “It has long been known that when a galaxy falls into a cluster, interactions with other cluster galaxies and with hot gas accelerate the shut off of its star formation relative to that of a similar galaxy in the field, in a process known as environmental quenching. The SpARCS team have developed new techniques using Spitzer Space Telescope infrared observations to identify hundreds of previously-undiscovered clusters of galaxies in the distant Universe.”
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. Gillian Wilson, professor of physics and astronomy at UC Riverside, added, “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.” ...
Stellar Mass Function of Cluster Galaxies at z ∼ 1.5:
Evidence for Reduced Quenching Efficiency at High Redshift - Julie B. Nantais et al
- arXiv.org > astro-ph > arXiv:1606.07832 > 24 Jun 2016