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

A. S. P. Afonso, D. Sobral, B. R. L. Ribeiro, J. Matthee, S. Santos, J. Calhau, K. Forster, A. Forshaw, A. Johnson, J. Merrick, S. Pérez Sánchez, O. Sheldon

Abstract
We investigate the rest-frame UV morphologies of a large sample of Lyman α emitters (LAEs) from z∼2 to z∼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 MUV∼−20, below MUV at these redshifts. We also focus our analysis on a subsample of 780 individual galaxies with iAB<25 for="" which="" galfit="" converges="" 429="" of="" them="" the="" individual="" median="" size="" r="" sub="">e∼1 kpc), ellipticities [slightly elongated with (b/a)∼0.45], Sérsic index (disc-like with n≲2), and light concentration (comparable to that of disc or irregular galaxies, with C∼2.7) of LAEs show mild evolution from z∼2 to z∼6. LAEs with the highest rest-frame equivalent widths (EWs) are the smallest/most compact (re∼0.8 kpc, compared to re∼1.5 kpc for the lower EW LAEs). When stacking our samples in bins of fixed Lyα luminosity and Lyα 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 Å. 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 ∼1 at z≳5 to SFGs being a factor of ∼2–4 larger than LAEs for z≲2. This means that at the highest redshifts, where typical sizes approach those of LAEs, the fraction of galaxies showing Lyα in emission (and with a high Lyα escape fraction) should be much higher, consistent with observations.

Keywords
galaxies: evolution; galaxies: high-redshift; galaxies: star formation; galaxies: structure

Monthly Notices of the Royal Astronomical Society
Volume 476, Issue 4, Page 23
2018 February

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Instituto de Astrofísica e Ciências do Espaço Universidade do Porto Faculdade de Ciências da Universidade de Lisboa
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia