On the UV compactness and morphologies of typical Lyman alpha emitters from z similar to 2 to z similar to 6

We investigate the rest-frame UV morphologies of a large sample of Lyman alpha emitters (LAEs) from z similar to 2 to z similar to 6, selected in a uniform way with 16 different narrow and medium bands over the full COSMOS field. We use 3045 LAEs with Hubble Space Telescope coverage in a stacking analysis and find that they have M-UV similar to -20, below M-UV* at these redshifts. We also focus our analysis on a subsample of 780 individual galaxies with i(AB) < 25 for which GALFIT converges for 429 of them. The individual median size (r(e) similar to 1 kpc), ellipticities [slightly elongated with (b/a) similar to 0.45], Sersic index (disc-like with n less than or similar to 2), and light concentration (comparable to that of disc or irregular galaxies, with C similar to 2.7) of LAEs show mild evolution from z similar to 2 to z similar to 6. LAEs with the highest rest-frame equivalent widths (EWs) are the smallest/most compact (r(e) similar to 0.8 kpc, compared to r(e) similar to 1.5 kpc for the lower EW LAEs). When stacking our samples in bins of fixed Ly alpha luminosity and Lya EW, we find evidence for redshift evolution in n and C, but not in galaxy sizes. The evolution seems to be stronger for LAEs with 25 < EW < 100 angstrom. When compared to other star-forming galaxies (SFGs), LAEs are found to be smaller at all redshifts. The difference between the two populations changes with redshift, from a factor of similar to 1 at z greater than or similar to 5 to SFGs being a factor of similar to 2-4 larger than LAEs for z less than or similar to 2. This means that at the highest redshifts, where typical sizes approach those of LAEs, the fraction of galaxies showing Ly alpha in emission (and with a high Ly alpha escape fraction) should be much higher, consistent with observations.