A population of red candidate massive galaxies ∼600 Myr after the Big Bang

Galaxies with stellar masses as high as roughly 10(11) solar masses have been identified(1-3) out to redshifts z of roughly 6, around 1 billion years after the Big Bang. It has been difficult to find massive galaxies at even earlier times, as the Balmer break region, which is needed for accurate mass estimates, is redshifted to wavelengths beyond 2.5 mu m. Here we make use of the 1-5 mu m coverage of the James Webb Space Telescope early release observations to search for intrinsically red galaxies in the first roughly 750 million years of cosmic history. In the survey area, we find six candidate massive galaxies (stellar mass more than 10(10) solar masses) at 7.4 <= z <= 9.1, 500-700 Myr after the Big Bang, including one galaxy with a possible stellar mass of roughly 10(11) solar masses. If verified with spectroscopy, the stellar mass density in massive galaxies would be much higher than anticipated from previous studies on the basis of rest-frame ultraviolet-selected samples.

Automated summary

Using early release observations from the James Webb Space Telescope, we have identified six candidate massive galaxies, including one with a possible stellar mass of 10^11 solar masses, within the first 750 million years of cosmic history. These findings suggest that the stellar mass density in massive galaxies may be higher than previously anticipated.