Star formation in distant galaxy clusters
In the distant universe, however, the picture is murkier, and some studies have even found the opposite, perhaps explaining in part the higher star formation rates then. Although studies of individual galaxies in the early universe have made progress, it is usually because these are extremely active and luminous galaxies. A cluster of galaxies, by contrast, might host one or two bright members but most of the membership is ordinary, faint, and hard to study. In fact, clusters are usually even difficult to identify.
CfA astronomers Matt Ashby, Brian Stalder, Tony Stark and their team of colleagues have studied star formation in very dense galaxy clusters in the early universe, dating from about six billion years after the big bang, in an effort to resolve the issue of star formation in cluster environments. They started with a sample of ultraluminous galaxies from the earlier, three billion year-old epoch (or even younger), discovered with the South Pole Telescope. These more distant galaxies were detected in part because their light has been gravitationally lensed by closer clusters; that is how the team was able to locate these clusters in the first place.
Knowing where to look, the scientists used infrared data from the Herschel and Planck Space Telescopes (and others) to examine the faint infrared signals from the clusters. That light is presumed to come from star formation, allowing the scientists to determine its level of activity and properties. Their principal finding is that the star formation activity is actually enhanced, not suppressed, in these clusters, up to several thousand new stars are forming per year in these clusters over-and-above the normal levels for these sets of galaxies. They also find that star formation is active out to the edges of clusters, perhaps fifteen million light-years across, and that the effect of this faint infrared emission needs to be taken into consideration in studies of origins of the cosmic background.
The findings are published in Monthly Notices of the Royal Astronomical Society.
Source: Harvard-Smithsonian Center for Astrophysics [February 13, 2016]