The origin of the observed Ly α EW distribution of dwarf galaxies at z ∼ 2

We present a rest-UV-selected sample of 32 lensed galaxies at z similar to 2 observed with joint Keck/LRIS rest-UV and Keck/MOSFIRE rest-optical spectra behind the clusters Abell 1689, MACS J0717, and MACS J1149. The sample pushes towards the faintest UV luminosities observed ( -19 <= M-UV <= -17) at this redshift. The fraction of dwarf galaxies identified as Ly alpha emitters (EW >= 20 A) is X-LAE = 33(-12)(+17) per cent . We use the Balmer lines and UV continuum to estimate both the intrinsic EW and the Ly alpha escape fraction to determine their relative importance in dictating the observed EW distribution. Fainter galaxies (M-UV > -19) show larger intrinsic EWs and escape fractions than brighter g alaxies. Only g alaxies with intrinsic EWs greater than 40 A have escape fractions larger than 5 per cent. We find little to no anticorrelation between the escape fraction and dust in dwarf galaxies. The volumetric escape fraction of our sample is f(esc)(Ly alpha) = 4.6(-1.4)(+ 2.0) per cent in agreement with measurements found elsewhere in the literature. 60 per cent of the total integrated Ly alpha luminosity density comes from galaxies with EWobs > 20 A.