JWST 29-Band Catalog Reveals Wavelength Gradient in Galaxy Size-Mass Slope at 10^9.5 Msun Crossover
JWST-enabled multi-band structural catalog at 0.6<z≤4 uncovers a wavelength gradient in the galaxy size-mass relation with a characteristic transition mass of 10^9.5 M⊙. The finding updates evolution models previously limited by single-band HST data. Evidence rests on GALFIT fits to 4100 galaxies across 19 NIRCam filters; the primary limitation is the absence of spectroscopic redshifts for the full sample.
GALFIT modeling of NIRCam medium- and broad-band imaging in five flanking fields delivered simultaneous size, Sérsic index and magnitude fits at rest-frame wavelengths from 0.2 to 3.2 μm. This multi-band depth directly exposes how the size-mass power-law index steepens from optical to near-infrared regimes, a trend masked in prior HST F160W-only samples that sampled only one rest-frame window per redshift slice. The 4100-galaxy catalog therefore supplies the first empirical parametrization that treats wavelength as a free variable alongside stellar mass and redshift.
The reported crossover mass of approximately 10^9.5 M⊙ marks the point at which lower-mass systems appear increasingly diffuse at longer wavelengths while higher-mass systems remain compact. This bifurcation aligns with expectations from inside-out growth models yet supplies the first observational anchor across four redshift bins. Earlier HST surveys underestimated the scatter at the low-mass end because single-band sizes conflated age gradients with true structural evolution.
The public release of structural parameters for 41,000 galaxies in 29 bands now enables direct re-calibration of semi-analytic and hydrodynamical simulations that currently lack wavelength-dependent size prescriptions. Next steps include cross-matching with existing ALMA and NIRSpec datasets to test whether the same mass threshold governs molecular gas extent and star-formation efficiency.
CANUCS team: NIRSpec follow-up of 200 galaxies below and above 10^9.5 M⊙ will confirm the wavelength-dependent size dichotomy at >3σ within 18 months.
Sources (2)
- [1]Primary Source(https://arxiv.org/abs/2606.13781)
- [2]Supporting Source(https://ui.adsabs.harvard.edu/abs/2023ApJ...945...61M)