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Star-forming galaxies form a sequence in the [OIII]/H-beta vs. [NII]/H-alphadiagnostic diagram, with low metallicity, highly ionized galaxies falling inthe upper left corner. Drawing from a large sample of UV-selected star-forminggalaxies at z~2 with rest-frame optical nebular emission line measurements fromKeck-MOSFIRE, we select the extreme ~5% of the galaxies lying in this upperleft corner, requiring log([NII]/H-alpha) <= 1.1 and log([OIII]/H-beta) >=0.75. These cuts identify galaxies with 12 + log(O/H) <~ 8.0, when oxygenabundances are measured via the O3N2 diagnostic. We study the Ly-alphaproperties of the resulting sample of 14 galaxies. The mean (median) rest-frameLy-alpha equivalent width is 39 (36) A, and 11 of the 14 objects (79%) areLy-alpha-emitters (LAEs) with W_Lya > 20 A. We compare the equivalent widthdistribution of a sample of 522 UV-selected galaxies at 2.0<z<2.6 identifiedwithout regard to their optical line ratios; this sample has mean (median)Ly-alpha equivalent width -1 (-4) A, and only 9% of these galaxies qualify asLAEs. The extreme galaxies typically have lower attenuation at Ly-alpha thanthose in the comparison sample, and have ~50% lower median oxygen abundances.Both factors are likely to facilitate the escape of Ly-alpha: in less dustygalaxies Ly-alpha photons are less likely to be absorbed during multiplescatterings, while the harder ionizing spectrum and higher ionization parameterassociated with strong, low metallicity star formation may reduce the coveringfraction or column density of neutral hydrogen, further easing Ly-alpha escape.The use of nebular emission line ratios may prove useful in the identificationof galaxies with low opacity to Ly-alpha photons across a range of redshifts.

A High Fraction of Ly-alpha-Emitters Among Galaxies with Extreme Emission Line Ratios at z ~ 2