EVIDENCE FOR SPATIALLY COMPACT Lyα EMISSION IN z=3.1 Lyα-EMITTING GALAXIES

We present the results of a high spatial resolution study of the line emission in a sample of z = 3.1 Ly alpha-emitting galaxies (LAEs) in the Extended Chandra Deep Field-South. Of the eight objects with coverage in our HST/WFPC2 narrowband imaging, two have clear detections and two are barely detected (similar to 2 sigma). The clear detections are within similar to 0.5 kpc of the centroid of the corresponding rest-UV continuum source, suggesting that the line-emitting gas and young stars in LAEs are spatially coincident. The brightest object exhibits extended emission with a half-light radius of similar to 1.5 kpc, but a stack of the remaining LAE surface brightness profiles is consistent with the WFPC2 point-spread function. This suggests that the Ly alpha emission in these objects originates from a compact (less than or similar to 2 kpc) region and cannot be significantly more extended than the far-UV continuum emission (less than or similar to 1 kpc). Comparing our WFPC2 photometry to previous ground-based measurements of their monochromatic fluxes, we find at 95% (99.7%) confidence that we cannot be missing more than 22% (32%) of the Ly alpha emission.