The formation of galaxies by gradual hierarchical co-assembly of baryons and cold dark matter halos is a fundamental paradigm underpinning modern astrophysics and predicts a strong decline in the number of massive galaxies at early cosmic times. Extremely massive quiescent galaxies have been observed as early as 1-2 billions years after the Big Bang. These are extremely constraining on theoretical models as they form 300 to 500 million years earlier and only some models can form massive galaxies this early. The spectrum of the newly-discovered quiescent galaxy ZF-UDS-7329 reveals features typical of much older stellar populations. Detailed modeling shows the stellar population formed around 1.5 billion years earlier in time at an epoch when dark matter halos of sufficient hosting mass have not yet assembled in the standard scenario. This observation may point to the presence of undetected populations of early galaxies and the possibility of significant gaps in our understanding of early stellar populations, galaxy formation and/or the nature of dark matter.
This Webb image shows ZF-UDS-7329, a rare massive galaxy that formed very early in the Universe. Image credit: Glazebrook et al., doi: 10.1038/s41586-024-07191-9.
The formation of galaxies is a fundamental paradigm underpinning modern astrophysics and predicts a strong decline in the number of massive galaxies in early cosmic times.
Extremely massive quiescent galaxies have now been observed as early as 1-2 billion years after the Big Bang which challenges previous theoretical models.
“We’ve been chasing this particular galaxy for seven years and spent hours observing it with the two largest telescopes on earth to figure out how old it was,” said Swinburne University of Technology’s Professor Karl Glazebrook.
“But it was too red and too faint, and we couldn’t measure it. In the end, we had to go off earth and use Webb to confirm its nature.”
“This was very much a team effort, from the infrared sky surveys we started in 2010 that led to us identifying this galaxy as unusual, to our many hours on the Keck and Very Large Telescope where we tried, but failed to confirm it, until finally the last year where we spent enormous effort figuring out how to process the Webb data and analyze this spectrum.”
“We are now going beyond what was possible to confirm the oldest massive quiescent monsters that exist deep in the Universe,” said Dr. Themiya Nanayakkara, an astronomer at the Swinburne University of Technology.
“This pushes the boundaries of our current understanding of how galaxies form and evolve.”
“The key question now is how they form so fast very early in the Universe and what mysterious mechanisms leads to stopping them forming stars abruptly when the rest of the Universe doing so.”
“Galaxy formation is in large part dictated by how dark matter concentrates.”
“Having these extremely massive galaxies so early in the Universe is posing significant challenges to our standard model of cosmology.”
“This is because we don’t think such massive dark matter structures as to host these massive galaxies have had time yet to form.”
“More observations are needed to understand how common these galaxies may be and to help us understand how truly massive these galaxies are.”
“This could be a new opening for our understanding of the physics of dark matter,” Professor Glazebrook said.
“Webb has been finding increasing evidence for massive galaxies forming early in time.”
“This result sets a new record for this phenomenon. Although it is very striking, it is only one object. But we hope to find more; and if we do this will really upset our ideas of galaxy formation.”
The discovery is reported in a paper published this week in the journal Nature.
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K. Glazebrook et al. A massive galaxy that formed its stars at z ~ 11. Nature, published online February 14, 2024; doi: 10.1038/s41586-024-07191-9
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