Ly$\alpha$ and UV Sizes of Green Pea Galaxies
  Green Peas are nearby analogs of high-redshift Ly$\alpha$-emitting galaxies. To probe their Ly$\alpha$ escape, we study the spatial profiles of Ly$\alpha$ and UV continuum emission of 24 Green Pea galaxies using the Cosmic Origins Spectrograph (COS) on Hubble Space Telescope (HST). We extract the spatial profiles of Ly$\alpha$ emission from their 2D COS spectra, and of UV continuum from both the 2D spectra and NUV images. The Ly$\alpha$ emission shows more extended spatial profiles than the UV continuum in most Green Peas. The deconvolved Full Width Half Maximum (FWHM) of the Ly$\alpha$ spatial profile is about 2 to 4 times that of the UV continuum in most cases. Since Green Peas are analogs of high-z LAEs, it suggests that most high-z LAEs likely have larger Ly$\alpha$ sizes than UV sizes. We also compare the spatial profiles of Ly$\alpha$ photons at blueshifted and redshifted velocities in eight Green Peas with sufficient data quality, and find the blue wing of the Ly$\alpha$ line has a larger spatial extent than the red wing in four Green Peas with comparatively weak blue Ly$\alpha$ line wings. We show that Green Peas and MUSE $z=3-6$ LAEs have similar Ly$\alpha$ and UV continuum sizes, which probably suggests starbursts in both low-z and high-z LAEs drive similar gas outflows illuminated by Ly$\alpha$ light. Five Lyman continuum (LyC) leakers in this sample have similar Ly$\alpha$ to UV continuum size ratios (~1.4-4.3) to the other Green Peas, indicating their LyC emission escape through ionized holes in the interstellar medium. 
Huan Yang, Sangeeta Malhotra, James E. Rhoads, Claus Leitherer, Aida   Wofford, Tianxing Jiang, Junxian Wang
astro-ph.GA