TNG300 Shows JWST/NIRCam Selections Capture Only 6% of z~5 Galaxies Above 10^11 Solar Masses
TNG300 mocks demonstrate that current JWST/NIRCam high-redshift massive-galaxy selections recover only a small fraction of the true high-mass population at z~5 and that these objects are seldom direct progenitors of today's most massive galaxies. The work supplies a revised selection that improves completeness without increasing contamination and cautions against over-interpreting early JWST candidates as the seeds of local giants.
The Baxter et al. analysis tests photometric criteria from Pérez-González and others on dust-attenuated mock photometry drawn from the TNG300 volume. Only the Pérez-González selection proves both reliable and inclusive, yet it still excludes 17 of the 18 most massive objects because their rest-frame colors fall outside the redder observational windows. An improved color-magnitude cut recovers a more complete high-mass sample while rejecting low-mass dusty interlopers that contaminate earlier criteria.
Descendant tracking reveals that NIRCam-selected massive galaxies at z=7, 4, and 2 rarely become the z=0 most-massive systems unless they experience substantial merger-driven growth after z~0.2. This decouples the JWST candidates from direct progenitor status and aligns with earlier findings that star-formation efficiency must rise sharply at early times to match observed stellar masses. The result echoes the tension first quantified in Labbe et al. 2023 and Boylan-Kolchin 2023, where number densities exceed Lambda-CDM expectations by factors of 3-10.
Future wide-area NIRCam surveys paired with deeper spectroscopy will test whether the missing redder population exists or whether dust and star-formation prescriptions in simulations require revision. If the improved selection yields number densities still exceeding TNG300 predictions, the discrepancy will constrain both feedback timing and the high-redshift initial mass function.
The simulation volume and dust model remain the chief limitations; larger volumes and varied attenuation curves are needed to confirm the fraction of missed massive galaxies.
Baxter et al.: Fewer than 5% of z=5 galaxies above 10^11 M_sun in TNG300-2 will satisfy the revised NIRCam cut once dust attenuation is varied by +/-0.3 mag in future runs released by 2027.
Sources (3)
- [1]Primary Source(https://arxiv.org/abs/2607.08820)
- [2]Supporting Source(https://arxiv.org/abs/2207.12446)
- [3]Supporting Source(https://arxiv.org/abs/2302.03050)