The Importance Of Star Formation Intensity In LYα Escape From Green Pea Galaxies And Lyman Break Galaxy Analogs

Abstract: We have studied ultraviolet images of 40 Green Pea galaxies and 15 local Lyman Break Galaxy Analogs to understand the relation between Ly$\alpha$ photon escape and central UV photometric properties. We measured star formation intensity (SFI, star formation rate per unit area) from the central 250 pc region ($S_{\rm 250pc}$) using COS/NUV images from the \textit{Hubble Space Telescope}. The measured $S_{\rm 250pc}$ of our sample Green Peas ranges from 2.3--46 $M_{\odot} \ \rm{year}^{-1} \ \rm{kpc^{-2}}$, with a geometric mean of $15 M_{\odot} \ \rm{year}^{-1} \ \rm{kpc^{-2}}$ and a standard deviation of 0.266 dex, forming a relatively narrow distribution. The Lyman Break Galaxy Analogs show a similarly narrow distribution of $S_{\rm 250pc}$ (0.271 dex), though with a larger mean of 28 $M_{\odot} \ \rm{year}^{-1} \ \rm{kpc^{-2}}$. We show that while the Ly$\alpha$ equivalent width (EW(Ly$\alpha$)) and the Ly$\alpha$ escape fraction ($f^{Ly\alpha}_{esc}$) are not significantly correlated with the central SFI ($S_{\rm 250pc}$), both are positively correlated with the ratio of surface brightness to galaxy stellar mass ($S_{\rm 250pc}/M_{\rm star}$), with correlation coefficients ($p$-values) of 0.702 ($1\times 10^{-8}$) and 0.529 ($5\times 10^{-4}$) with EW(Ly$\alpha$) and $f^{Ly\alpha}_{esc}$, respectively. These correlations suggest a scenario where intense central star formation can drive a galactic wind in galaxies with relatively shallow gravitational potential wells, thus clearing channels for the escape of Ly$\alpha$ photons.