Compact Size, High $\hat{I}\pounds$SFR: Defining Morphological Features of Ly$\hat{I}\pm$-Emitters

Abstract

The mechanisms of Ly$\hat{I}\pm$ photon escape are key to understanding galaxy evolution and cosmic reionization, yet remain poorly understood. We investigate the UV-continuum sizes of 23 Ly$\hat{I}\pm$ emitters (LAEs) at Cosmic Noon ($1.7<z<3.3$), extending previous size analyses to include fainter galaxies ($M_{\mathrm{UV}}\simeq -14$) using gravitational lensing. Our results show that these LAEs are unusually small for their luminosity, with a mean effective radius ($r_{\mathrm{eff}}$) of $170\pm 140$ pc. They follow a distinct size-luminosity relation, with an intercept at $M_{\mathrm{UV}}=-21$ approximately three times smaller than typical star-forming galaxies (SFGs) at similar redshifts. This relation, however, is consistent with that of low-redshift Green Pea galaxies, suggesting that LAEs maintain compact sizes across redshifts. We also find that Ly$\hat{I}\pm$ equivalent width (EW(Ly$\hat{I}\pm$)) increases with decreasing $r_{\mathrm{eff}}$, confirming previous findings. The small sizes of LAEs lead to high star formation surface densities ($\hat{I}\pounds$SFR $=1-600M_{\odot }{\mathrm{yr}}^{-1}\mathrm{kp}{\mathrm{c}}^{-2}$), clearly separating them from typical SFGs in the $\hat{I}\pounds$SFR vs. $r_{\mathrm{eff}}$ space. Given that high $\hat{I}\pounds$SFR is linked to strong galactic outflows, our findings imply that compact morphology plays a key role in Ly$\hat{I}\pm$ escape, likely facilitated by outflows that clear under-dense channels in the ISM. Thus, these results demonstrate that compact size and high $\hat{I}\pounds$SFR can help identify Ly$\hat{I}\pm$-emitters.

13 pages, 5 figures, 1 table. Accepted for publication by ApJ