In this protocluster there is a mysteriously high number of dead galaxies
Clusters of galaxies grow over time thanks to gravity and, in the current universe, can contain hundreds or even thousands of galaxies, as well as hot gas and dark matter. Over time, their galaxies burn the available fuel and evolve from vigorous galaxies to red and dead galaxies.
"In the early universe, all protoclusters discovered so far are full of galaxies that form in energetic manner stars, ”said Ian McConachie, a graduate student in the UC Riverside Department of Physics and Astronomy and lead author of the research paper published in The Astrophysical Journal. "But incredibly, unlike all the other protoclusters that have been found ... many galaxies in MAGAZ3NE J0959 seem to have already stopped forming stars."
Co-author Gillian Wilson, professor of physics and astronomy at UCR in whose laboratory works McConachie, stated that J0959 was discovered by the "Massive Ancient Galaxies At Z> 3 NEar-infrared", or MAGAZ3NE, an investigation designed to discover and study ultramassive galaxies and their neighbors.
"We are seeing this protocluster as it appeared when the universe was less than 2 billion years old," he said. "It's like taking a cluster like Coma, the closest galaxy-rich cluster to Earth, and inserting it into the early universe."
Credits: Hubble NASA / ESA
Co-author Benjamin Forrest, a former postdoctoral researcher in Wilson's lab now based at UC Davis, explained that at the heart of MAGAZ3NE J0959 is an ultramassive galaxy that has already formed a mass of over 200 billion suns.
"Why this ultra-massive galaxy and so many of its neighbors formed most of their stars and then went dormant when the universe was still so young, in contrast to other protoclusters known at the same time, it is a great mystery, ”he said. “Why its galaxies are so different from those of all other known protoclusters, and so similar to those of Coma, is a mystery.”
Forrest added that MAGAZ3NE J0959 was discovered from the ground, but the advent of powerful new tools, such as the recently launched James Webb Space Telescope, should soon reveal whether there are other protoclusters like MAGAZ3NE J0959 full of dead galaxies waiting to be found in the early universe.
“If such protoclusters were found in large numbers, it would mean that the current paradigm of protocluster formation would require a major overhaul, ”Forrest explained. "A new scenario of protoclusters existing in a diversity of states in the early universe should be adopted. With many member galaxies extinguishing in the first two billion years, this would almost certainly pose a significant challenge to current galactic simulation models. ”
The team used spectroscopic observations from the W.M. Keck Observatory's Multi-Object Spectrograph for Infrared Exploration, or MOSFIRE, to make detailed measurements of MAGAZ3NE J0959 and precisely quantify its distances.
Closely associated with the question of how ultramassive galaxies are formed is the question of environment in which they are formed, for example, are they always found in too dense environments such as protoclusters, or can they also form in isolation? Next, the team plans to study the neighborhoods of all other ultramassive galaxies in the MAGAZ3NE survey to answer this question.
