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.2023;7(6):731-735.
doi: 10.1038/s41550-023-01937-7. Epub 2023 Apr 13.

Stress testingΛ CDM with high-redshift galaxy candidates

Affiliations

Stress testingΛ CDM with high-redshift galaxy candidates

Michael Boylan-Kolchin. Nat Astron.2023.

Abstract

Early data from the James Webb Space Telescope (JWST) have revealed a bevy of high-redshift galaxy candidates with unexpectedly high stellar masses. An immediate concern is the consistency of these candidates with galaxy formation in the standardΛCDM cosmological model, wherein the stellar mass (M⋆) of a galaxy is limited by the available baryonic reservoir of its host dark matter halo. The mass function of dark matter haloes therefore imposes an absolute upper limit on the number densityn (>M⋆,z) and stellar mass densityρ⋆ (>M⋆,z) of galaxies more massive thanM⋆ at any epochz. Here I show that the most massive galaxy candidates in JWST observations atz ≈ 7-10 lie at the very edge of these limits, indicating an important unresolved issue with the properties of galaxies derived from the observations, how galaxies form at early times inΛCDM or within this standard cosmology itself.

Keywords: Cosmology; Galaxies and clusters.

© The Author(s) 2023.

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Conflict of interest statement

Competing interestsThe author declares no competing interests.

Figures

Fig. 1
Fig. 1. Limits on the abundance of galaxies as a function of redshift.
Curves show the relationship betweenM⋆ andz at fixed cumulative halo abundance (left) and fixedρb (>Mhalo), or equivalently fixed peak heightν (right). The most extreme L23 galaxy candidates are shown as blue stars, with uncertainties indicating 68% intervals (symmetric about the median) of the posterior probability distribution. The existence of a galaxy withM⋆ at redshiftz requires that such galaxies have a cumulative co-moving number density that is, at most, the number density shown in the left panel, as those galaxies must reside in host halo of massMhalo = M⋆/(fbϵ). The cumulative co-moving number density corresponding to an observedM⋆ will probably be (much) smaller than is indicated here, as the curves are placed on the plot by assuming the physically maximalϵ = 1.0. For smaller values ofϵ, the curves in each panel move down relative to the points by a factor ofϵ (as indicated by the black downward-facing arrows). The right panel demonstrates that even for the most conservative assumption ofϵ = 1.0, the data points correspond to very rare peaks in the density field, implying a limited baryonic reservoir that is in tension with the measured stellar masses of the galaxies.
Fig. 2
Fig. 2. Stellar mass density limits.
The co-moving stellar mass density contained within galaxies more massive thanM⋆ atz ≈ 9.1 (left) andz ≈ 7.5 (right) for three values of the assumed conversion efficiencyϵ of a halo’s cosmic allotment of baryons into stars. Only if all available baryons in all haloes with enough baryons to form the galaxies reported by L23 have indeed been converted into stars by that point—an unrealistic limit—is it possible to produce the stellar mass density in the highestM⋆ bin atz ≈ 9 measured by L23 in a typical volume of aΛCDM Universe with the Planck 2020 cosmology. Results are similar atz ≈ 7.5. For more realistic values ofϵ, the required baryon reservoir is substantially larger than the theoretical maximum in this cosmology. When considering 1 σ shot noise and sample variance errors added in quadrature (which comprise the uncertainties on the L23 data points in each panel), the measurements are consistent with the baseΛCDM model ifϵ > 0.57, which would still imply incredibly efficient star formation in the high-redshift Universe.
See this image and copyright information in PMC

References

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