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Arxiv: Early Results from GLASS-JWST XXIII: The transmission of Lyman-alpha from UV-faint z ~ 3-6 galaxies Published: 4/5/2023 9:00:45 PM Updated: 1/2/2024 2:31:21 PM

Paper abstract: Lyman-alpha (Ly\alpha) emission from galaxies can be used to trace neutralhydrogen in the epoch of reionization, however, there is a degeneracy betweenthe attenuation of Ly\alpha in the intergalactic medium (IGM) and the lineprofile emitted from the galaxy. Large shifts of Ly\alpha redward of systemicdue to scattering in the interstellar medium can boost Ly\alpha transmissionin the IGM during reionization. The relationship between Ly\alpha velocityoffset from systemic and other galaxy properties is not well-established athigh-redshift or low luminosities, due to the difficulty of observing emissionlines which trace systemic redshift. Rest-frame optical spectroscopy withJWST/NIRSpec has opened a new window into understanding of Ly\alpha at z>3.We present a sample of 12 UV-faint galaxies (-20 <~ MUV <~ -16)at 3 <~ z <~ 6, with Ly\alpha velocity offsets, \Deltav_{\mathrm{Ly}\alpha}, measured from VLT/MUSE and JWST/NIRSpec from theGLASS-JWST Early Release Program. We find median \Delta v_{\mathrm{Ly}\alpha}of 205 km s^{-1} and standard deviation 75 km s^{-1}, compared to 320 and170km s^{-1} for MUV < -20 galaxies in the literature. Our new sampledemonstrates the previously observed trend of decreasing Ly\alpha velocityoffset with decreasing UV luminosity and optical line velocity dispersion,extends to MUV \gtrsim -20, consistent with a picture where the Ly\alphaprofile is shaped by gas close to the systemic redshift. Our results imply thatduring reionization Ly\alpha from UV-faint galaxies will be preferentiallyattenuated, but that detecting Ly\alpha with low \Deltav_{\mathrm{Ly}\alpha} can be an indicator of large ionized bubbles.