2022ApJ...939L..31H

The James Webb Space Telescope (JWST) discovered several luminous high-redshift galaxy candidates with stellar masses of M_* ≳ 10⁹M_⊙ at photometric redshifts z_phot ≳ 10, which allows to constrain galaxy and structure formation models. For example, Adams et al. identified the candidate ID 1514 with ${\mathrm{log}}_{10}({M}_{* }/{M}_{\odot })={9.8}_{-0.2}^{+0.2}$ located at ${z}_{\mathrm{phot}}={9.85}_{-0.12}^{+0.18}$ and Naidu et al. found even more distant candidates labeled as GL-z11 and GL-z13 with ${\mathrm{log}}_{10}({M}_{* }/{M}_{\odot })={9.4}_{-0.3}^{+0.3}$ at ${z}_{\mathrm{phot}}={10.9}_{-0.4}^{+0.5}$ and ${\mathrm{log}}_{10}({M}_{* }/{M}_{\odot })={9.0}_{-0.4}^{+0.3}$ at ${z}_{\mathrm{phot}}={13.1}_{-0.7}^{+0.8}$, respectively. Assessing the computations of the IllustrisTNG (TNG50-1 and TNG100-1) and EAGLE projects, we investigate if the stellar mass buildup as predicted by the ΛCDM paradigm is consistent with these observations assuming that the early JWST calibration is correct and that the candidates are indeed located at z ≳ 10. Galaxies formed in the ΛCDM paradigm are by more than an order of magnitude less massive in stars than the observed galaxy candidates implying that the stellar mass buildup is more efficient in the early universe than predicted by the ΛCDM models. This in turn would suggest that structure formation is more enhanced at z ≳ 10 than predicted by the ΛCDM framework. We show that different star formation histories could reduce the stellar masses of the galaxy candidates alleviating the tension. Finally, we calculate the galaxy-wide initial mass function (gwIMF) of the galaxy candidates assuming the integrated galaxy IMF theory. The gwIMF becomes top-heavy for metal-poor star-forming galaxies decreasing therewith the stellar masses compared to an invariant canonical IMF.