Abstract
Lyman-a (Lya) is, intrinsically, the strongest nebular emission line in
actively star-forming galaxies (SFGs), but its resonant nature and uncertain
escape fraction limit its applicability. The structure, size, and morphology
may be key to understand the escape of Lya photons and the nature of Lya
emitters (LAEs). We investigate the rest-frame UV morphologies of a large
sample of ~4000 LAEs from z~2 to z~6, selected in a uniform way with 16
different narrow- and medium-bands over the full COSMOS field (SC4K, Santos et
al. in prep). From the magnitudes that we measure from UV stacks, we find that
these galaxies are populating the faint end of the UV luminosity function. We
find also that LAEs have roughly the same morphology from z~2 to z~6. The
median size (re~1 kpc), ellipticities (slightly elongated with b/a~0.45),
Sérsic index (disk-like with n<2), and light concentration (comparable to
that of disk or irregular galaxies, with C~2.7) show little to no evolution.
LAEs with the highest equivalent widths (EW) are the smallest/most compact
(re~0.8 kpc, compared to re~1.5 kpc for the lower EW LAEs). In a scenario where
galaxies with a high Lya escape fraction are more frequent in compact objects,
these results are a natural consequence of the small sizes of LAEs. When
compared to other SFGs, LAEs are found to be smaller at all redshifts. The
difference between the two populations changing 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 Lya in emission should be much higher, consistent
with observations.
Description
[1709.04470] On the UV compactness and morphologies of typical Lyman-a emitters from z~2 to z~6
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