JWST Treasury Proposal Targets Black Hole Seeding Pathways Through Little Red Dot Demographics

The proposal outlines grating spectroscopy, deep MIRI imaging, and repeated-field variability monitoring to build black hole mass functions and Eddington-ratio distributions down to 10^6 solar masses. These measurements would test whether heavy seeds from direct collapse or lighter Pop III remnants dominate early populations, a distinction erased by later accretion. Current JWST data show LRD number densities and BH-to-stellar mass ratios that already strain standard models, yet lack the uniform selection and time baseline needed to break degeneracies.

Related work from Matthee et al. (2024) on broad-line LRDs and Greene et al. (2024) on overmassive black holes at z~5-7 supplies the empirical tension the program aims to resolve. The white paper correctly identifies that single-epoch spectra cannot disentangle seed mass from duty cycle, but understates the calibration challenge: host-galaxy dust properties at these redshifts remain poorly constrained, risking systematic offsets in virial masses that could mimic seeding signatures.

A coordinated Treasury program would also enable cross-checks with ALMA [C II] kinematics and future Roman wide-field variability, tightening co-evolution constraints. Without it, the field risks accumulating heterogeneous datasets that perpetuate the same ambiguities the proposal seeks to eliminate.

Next steps hinge on Cycle 4-5 decisions; if approved, first-epoch spectroscopy could begin by 2027, delivering initial mass-function constraints within three years.