Astronomers from the University of Cambridge and elsewhere have analyzed the spectroscopic and photometric data from three instruments (NIRSpec, NIRISS and NIRCam) on board the NASA/ESA/CSA James Webb Space Telescope to identify galaxies at similar distances and with similar colors behind the lensing galaxy cluster SMACS J0723.3-7327.

This Webb image shows members of the SMACS0723_PC protocluster: the red circles show the position of the two spectroscopically confirmed galaxies and the green circles are at the position of the six other protocluster members candidates. Image credit: Laporte et al., arXiv: 2208.04930.

“Understanding the formation and evolution of the first population of galaxies a few million years after the Big Bang is one of the most active topics of current extragalactic astronomy,” said Dr. Nicolas Laporte from the Kavli Institute for Cosmology and the Cavendish Laboratory at the University of Cambridge and his colleagues.

“For decades, instruments have been built to push even further our observational limits.”

“The current most distant and detailed picture of the Universe, the Cosmic Microwave Background, has been obtained by ESA’s Planck mission.”

“It shows that already 380,000 years after the Big Bang, the matter density in the Universe was inhomogeneously distributed, suggesting that small amplitude density fluctuations were on-going in the early phase of the Universe.”

“These fluctuations grow and eventually the denser regions collapse to form the first bound objects. Moreover, the first dark matter haloes undergo a process of fragmentation, suggesting that the most massive galaxies may have formed in overdense regions — so-called protoclusters.”

“The successful launch of Webb on December 25, 2021 from Europe’s Spaceport in French Guyana has opened a new window to study protoclusters,” they added.

“Its unprecedented sensitivity will allow the community to identify and spectroscopically confirm bright galaxies, but also fainter galaxies at similar redshifts.”

In their study, Dr. Laporte and co-authors analyzed the first dataset released by Webb to search for protoclusters at high redshifts behind the lensing cluster SMACS J0723.3-7327.

They were able to identify a group of at least eight galaxies with similar colors at a redshift of z=7.66.

Named SMACS0723_PC, this protocluster sits so far away that its light took 13 billion years to reach Earth.

“Based on several methods, we estimate the total dark matter halo mass of SMACS0723_PC to be 3.6*1011 solar masses,” the researchers said.

“This value agrees perfectly with what is expected for progenitors of a Coma-like cluster.”

“Furthermore, the star-formation main sequence at z≥7 and the estimated size are in line with expectations.”

“This detection adds to just a few protoclusters currently known in the first billion years of the Universe,” they added.

“Such distant protoclusters may play an important role in cosmic reionization.”

source: sci.news