Two Protoclusters of Galaxies Spotted in Early Universe

by johnsmith

Each of the two newly-discovered protoclusters, MAGAZ3NE J095924+022537 and MAGAZ3NE J100028+023349 (MAGAZ3NE J0959 and MAGAZ3NE J1000 for short), hosts an ultramassive galaxy — the progenitor of brightest cluster galaxies seen in modern-day massive galaxy clusters — in its center. Notably, and in marked contrast to previously discovered protoclusters, MAGAZ3NE J0959 contains a high fraction of quiescent galaxies.

Density distribution of the 550 galaxies in the COSMOS UltraVISTA DR3 catalog (cyan circles). The two ultramassive galaxies, COS-DR3-179370 (in MAGAZ3NE J0959) and COS-DR3-160748 (in MAGAZ3NE J1000), are shown by blue and green stars, respectively. Image credit: McConachie et al., doi: 10.3847/1538-4357/ac2b9f.

Density distribution of the 550 galaxies in the COSMOS UltraVISTA DR3 catalog (cyan circles). The two ultramassive galaxies, COS-DR3-179370 (in MAGAZ3NE J0959) and COS-DR3-160748 (in MAGAZ3NE J1000), are shown by blue and green stars, respectively. Image credit: McConachie et al., doi: 10.3847/1538-4357/ac2b9f.

Galaxy clusters grow over time under gravity and, in the present-day Universe, can contain hundreds or even thousands of galaxies, as well as hot gas and dark matter.

As time goes by, their galaxies burn through the fuel available and evolve from vigorously star-forming galaxies into red and dead galaxies.

“In the early Universe, all protoclusters discovered until now are full of vigorously star-forming galaxies,” said Ian McConachie, a graduate student in the Department of Physics and Astronomy at the University of California, Riverside.

“But incredibly, unlike all of the other protoclusters that have been found at this epoch, many galaxies in MAGAZ3NE J0959 appear to have already stopped forming stars.”

MAGAZ3NE J0959 and MAGAZ3NE J1000 were discovered by the Massive Ancient Galaxies At Z > 3 NEar-infrared (MAGAZ3NE) survey.

The first protocluster consists of at least 38 protocluster members, and is about 11.8 billion light-years away from Earth.

The second protocluster has a total of 20 member galaxies, including a post-starburst ultramassive galaxy, and is slightly farther away.

“We are seeing this protocluster as it appeared when the Universe was less than 2 billion years old,” said Professor Gillian Wilson, an astronomer in the Department of Physics and Astronomy at the University of California, Riverside.

“It is as if you took a cluster like the Coma Cluster, the nearest rich cluster of galaxies to Earth, and plopped it into the early Universe.”

“At the heart of MAGAZ3NE J0959 is an ultramassive galaxy that has already formed a mass of more than 200 billion suns,” added Dr. Benjamin Forrest, also from the Department of Physics and Astronomy at the University of California, Riverside.

“Why this ultramassive galaxy and so many of its neighbors formed most of their stars and then became inactive when the Universe was still so young, in contrast to other known protoclusters from the same time, is a big mystery.”

“Why its galaxies are so unlike those in all the other known protoclusters, and so similar to those in Coma Cluster, is a complete mystery.”

“A new scenario of protoclusters existing in a diversity of states in the early Universe would have to be adopted,” he added.

“With many member galaxies quenching in the first two billion years, this would almost certainly pose significant challenges for current models of galaxy simulation.”

The study was published in the Astrophysical Journal.

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Ian McConachie et al. 2022. Spectroscopic Confirmation of a Protocluster at z = 3.37 with a High Fraction of Quiescent Galaxies. ApJ 926, 37; doi: 10.3847/1538-4357/ac2b9f

Source link: https://www.sci.news/astronomy/magaz3ne-protoclusters-10541.html

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