On the UV compactness and morphologies of typical Lyman α emitters from z ∼ 2 to z ∼ 6

Abstract

We investigate the rest-frame UV morphologies of a large sample of Lyman-a\nemitters (LAEs) from z~2 to z~6, selected in a uniform way with 16 different\nnarrow- and medium-bands over the full COSMOS field. We use 3045 LAEs with HST\ncoverage in a stacking analysis and find that they have M_UV~-20, below M*_UV\nat these redshifts. We also focus our analysis on a subsample of 780 individual\ngalaxies with i_AB<25 for which GALFIT converges for 429 of them. The\nindividual median size (re~1 kpc), ellipticities (slightly elongated with\n(b/a)~0.45), S\\'ersic index (disk-like with n<2) and light concentration\n(comparable to that of disk or irregular galaxies, with C~2.7) of LAEs show\nmild evolution from z~2 to z~6. LAEs with the highest rest-frame equivalent\nwidths (EW) are the smallest/most compact (re~0.8 kpc, compared to re~1.5 kpc\nfor the lower EW LAEs). When stacking our samples in bins of fixed Lya\nluminosity and Lya EW we find evidence for redshift evolution in n and C, but\nnot in galaxy sizes. The evolution seems to be stronger for LAEs with 25<EW<100\n{\\AA}. When compared to other SFGs, LAEs are found to be smaller at all\nredshifts. The difference between the two populations changes with redshift,\nfrom a factor of ~1 at z>5 to SFGs being a factor of ~2-4 larger than LAEs for\nz<2. This means that at the highest redshifts, where typical sizes approach\nthose of LAEs, the fraction of galaxies showing Lya in emission (and with a\nhigh Lya escape fraction) should be much higher, consistent with observations.\n