Physical origin of the redshift-dependent size–Lyα equivalent-width relation

Investigate the physical origin of the apparent strengthening of the anticorrelation between rest-frame optical size and Lyα equivalent width at z ≥ 4, distinguishing an intrinsic size–equivalent-width evolution from selection effects caused by intergalactic-medium attenuation.

Background

The study finds that more compact Lyα emitters tend to have larger Lyα equivalent widths, with the anticorrelation appearing stronger at z ≥ 4. However, the authors caution that this apparent redshift dependence is most prominent in one redshift bin and is only marginally detected in another. They state that its physical origin is unresolved and suggest that intergalactic-medium attenuation could alter the equivalent-width distribution of narrowband-selected sources, making it necessary to distinguish this selection effect from genuine evolution in the relationship between morphology and Lyα emission.

References

The apparent strengthening of the size--EW anticorrelation at $z \geq 4$ is most prominent in NB718 ($z = 4.90$) and marginally detected in NB816 ($z = 5.72$), and should be interpreted with caution; its physical origin remains unconstrained. One possible contributing factor is IGM attenuation at $z \gtrsim 4$, which reduces the observed Ly$\alpha$ flux and may alter the EW distribution of narrowband-selected LAEs; larger samples spanning multiple narrowband bins at $z > 4$ are needed to distinguish this selection effect from an intrinsic size--EW evolution.

— Rest-Frame UV and Optical Structural Evolution of Narrowband-Selected Lyman-alpha Emitters at z = 2-7 with JWST/NIRCam  (2609.25886 - Laishram et al., 22 Sep 2026) in Section 5.2, Star Formation Rate Surface Density and Lyα Escape