Source: Chworowsky et al. 2024, cleaner CEERS massive-galaxy census
Source: Chworowsky et al. 2024, cleaner CEERS massive-galaxy census
Question/approach: How abundant are massive (stellar mass >10 billion solar masses) galaxies from z=4–8 after careful catalogue vetting, AGN screening and propagation of mass-fitting, Poisson and cosmic-variance uncertainties? They visually inspected 561 possible high-redshift massive sources and removed 300 after vetting, including likely AGN for which stellar light cannot be safely separated from nuclear light. This does not mean 300 were all the original Labbé six, or that each had its mass revised by a fixed factor.
What survived: The abundance exceeds many contemporary galaxy-formation models, especially above z≈5. The authors find it consistent with ΛCDM if baryon-to-star conversion becomes more efficient at early times, or if the assumed mass-to-light ratio is lower (e.g. stellar initial-mass function differences). It is incorrect to paraphrase their conclusion as “there are no surprisingly massive galaxies.” Clustering measurements could distinguish a change in halo occupation/efficiency from a changed mass-to-light ratio. A separately published Somerville et al. 2023 analysis notes that an instrument calibration update changed some early Labbé masses; this is distinct from Chworowsky’s new survey selection.
Related: original claims and open question.