The Compact UV Size of Green Pea Galaxies As Local Analogs of High-redshift Lyα-Emitters

Abstract

We study the dependence of Ly α escape from galaxies on UV continuum size and luminosity using a sample of 40 Green Pea (GP) galaxies, which are the best local analogs of high-redshift Ly α emitters (LAEs). We use the Cosmic Origins Spectrograph near-ultraviolet images from the Hubble Space Telescope to measure the UV size and luminosity with 0.″047 spatial resolution. Like most galaxies the GPs show a log-normal size distribution. They also show a positive correlation between size and UV-continuum luminosity. The slope of the size-continuum luminosity relation for GPs is consistent with those of continuum-selected star-forming galaxies (SFGs) at low and high redshifts. A distinctive feature of GPs is a very compact typical radius of 0.33 kpc with a population spread (1 σ ) of 0.19 kpc. The peak of the size distribution and the intercept of the size–luminosity relation of GPs are noticeably smaller than those of continuum-selected SFGs at similar redshifts. There are statistically significant anticorrelations found between the circularized half-light radius ( r cir,50 ), the Ly α equivalent width (EW(Ly α )), and the Ly α escape faction ( ), suggesting that small UV-continuum radii are crucial for Ly α emission. GPs and high-redshift LAEs have similar sizes, once spatial resolution effects are properly considered. Our results show that a compact small size is crucial for escape of Ly α photons, and that Ly α emitters show constant characteristic size independent of their redshift.