JWST’s early, massive galaxies agree with ΛCDM cosmology

Since JWST’s launch, astronomers have used it to investigate the young Universe.

The Cosmic Evolution Early Release Science Survey (CEERS Survey) broke the record for largest deep-field image taken by JWST, previously held by the first lensing cluster image released. This small patch of sky, near the handle of the Big Dipper, contains some ~200 luminous disk galaxy candidates found within the first ~3 billion years of the Universe’s history. The deepest views of the early Universe have given astronomers and astrophysicists much to ponder.

With unprecedented technical capabilities, JWST has already broken Hubble’s cosmic distance record.

The viewing area of the JADES survey, along with the four most distant galaxies verified within this field-of-view. The three galaxies at z = 13.20, 12.63, and 11.58 are all more distant than the previous record-holder, GN-z11, which had been identified by Hubble and has now been spectroscopically confirmed by JWST to be at a redshift of z = 10.6. No doubt these records will themselves be broken, possibly with galaxy candidates that already exist within the same field-of-view.

Numerous ultra-distant galaxies have been uncovered, revealing a rich, early Universe.

This animation switches points of view between the Hubble Ultra Deep Field and the JWST view of an overlapping region of space. Because of the difference in telescope size and resolution, the JWST views are downsampled by about a factor of 4 in resolution to make these two images match.

These youthful galaxies appear massive, evolved, and are rapidly forming stars.

The galaxies that are members of the identified proto-cluster A2744z7p9OD are shown here, outlined atop their positions in the JWST view of galaxy cluster Abell 2744. At just 650 million years after the Big Bang, it’s the oldest proto-cluster of galaxies ever identified. This is early, but is consistent with simulations of when the earliest proto-clusters should emerge from the most initially overdense regions.

Although data is still incoming, many question whether these galaxies conflict with our consensus cosmology.

This collection of several different JWST “pointings” from the CEERS photometric survey contains Maisie’s Galaxy, a high-redshift galaxy candidate that was recently spectroscopically confirmed to be at z=11.4, placing it just 390 million years after the Big Bang. It also contains four separate, nearby galaxies at a confirmed redshift of 4.9, indicating a galaxy proto-cluster just 1.2 billion years after the Big Bang.

The initial conditions of our Universe are known: imprinted in the Big Bang’s leftover glow.

The large, medium, and small-scale fluctuations from the inflationary period of the early universe determine the hot and cold (underdense and overdense) spots in the Big Bang’s leftover glow. These fluctuations, which get stretched across the Universe in inflation, should be of a slightly different magnitude on small scales versus large ones: a prediction that was observationally borne out at approximately the ~3% level.

The equations that govern gravitation and structure formation are also highly certain.

The largest-scale observations in the Universe, from the cosmic microwave background to the cosmic web to galaxy clusters to individual galaxies, all require dark matter and dark energy to explain what we observe. While the equations that govern the evolution are well known, as are the magnitudes of the initially overdense regions in our Universe, obtaining the necessary small-scale resolution to tease out the masses and properties of the smallest, earliest galaxies remains difficult.

Therefore, we should successfully predict how massive structures can be all throughout cosmic history.

Over time, gravitational interactions will turn a mostly uniform, equal-density Universe into one with large concentrations of matter and huge voids separating them. For as long as radiation is still important, exerting an outward pressure even once the Universe becomes matter-dominated, the growth of matter imperfections is very small.

One underappreciated limitation of modern simulations, however, is resolution.

This snippet from a structure-formation simulation, with the expansion of the Universe scaled out, represents billions of years of gravitational growth in a dark matter-rich Universe. Over time, overdense clumps of matter grow richer and more massive, growing into galaxies, groups, and clusters of galaxies, while the less dense regions than average preferentially give up their matter to the denser surrounding areas. The “void” regions between the bound structures continue to expand, but the structures themselves do not.

Prior simulations had difficulty reproducing massive, evolved galaxies so early.

While the web of dark matter (purple, left) might seem to determine cosmic structure formation on its own, the feedback from normal matter (red, at right) can severely impact the formation of structure on galactic and smaller scales. Both dark matter and normal matter, in the right ratios, are required to explain the Universe as we observe it. Structure formation is hierarchical within the Universe, with small star clusters forming first, early protogalaxies and galaxies forming next, followed by galaxy groups and clusters, and lastly by the large-scale cosmic web.

With both greater mass resolution and spatial resolution, however, the Renaissance simulations offer a different perspective.

Although this table might appear to be just a jumble of numbers, the key to high resolution is the final two columns: lower masses and smaller spatial separations lead to higher-resolution simulations, which means more reliable predictions for structures at lower masses, on smaller scales, and at earlier times. Note how superior Renaissance is to all others in these regards.

The unprecedented resolution highlights just how much mass the most initially overdense regions accumulate.

Regions born with a typical, or “normal” overdensity, will grow to have rich structures in them, while underdense “void” regions will have less structure. However, early, small-scale structure is dominated by the most highly peaked regions in density (labeled “rarepeak” here), which grow the largest the fastest, and are only visible in detail to the highest resolution simulations.

Rare but strongly overdense regions grow to contain the earliest, most massive galaxies of all.

The three simulated regions highlighted earlier, using the Renaissance suite, lead to predictions for how massive galaxies should be in those three regions (orange, blue, and green lines). The 5 earliest galaxies revealed so far with JWST, with error bars shown, have about a probability of “1” of occurring within the observed regions. If they were truly rare, they’d be brighter and more massive, as shown by the ~10^-3 and ~10^-6 likelihood curves. Note that even at the start of the scale on the x-axis, at ~150 million years, clumps of stellar matter with ~100,000 solar masses already exist.

Even with modest, completely realistic star-formation rates, JWST’s most distant galaxies are perfectly typical within our standard ΛCDM cosmology.

Three different but still realistic estimates for sustained star-formation rates are given by the three lines, with model galaxies as revealed by simulations shown with shadings and the actual, JWST observed galaxies shown atop them. Note the 100% overlap.

Surprises and new records still await JWST, but claims like “JWST broke cosmology” were all premature.

This composite image from 7 of JWST’s NIRCam filters shows the central part of galaxy cluster Abell 2744: Pandora’s Cluster. The three main cluster components are highlighted with insets, with foreground and background objects, totaling some ~50,000 of them, present in this 0.007 square degree patch of sky.

Mostly Mute Monday tells an astronomical story in images, visuals, and no more than 200 words. Talk less; smile more.