Spectroscopic properties of the z≈4.5 Lyα emitters

We present Keck Low Resolution Imaging Spectrometer optical spectra of 17 Lyalpha-emitting galaxies and one Lyman break galaxy at z approximate to 4.5 discovered in the Large Area Lyman Alpha survey. The survey has identified a sample of similar to 350 candidate Lyalpha-emitting galaxies at z approximate to 4.5 in a search volume of 1.5 x 10(6) comoving Mpc(3). We targeted 25 candidates for spectroscopy; hence, the 18 confirmations presented herein suggest a selection reliability of 72%. The large equivalent widths (median W-lambda(rest) approximate to 80 Angstrom) but narrow physical widths (Deltav < 500 km s(-1)) of the Ly alpha emission lines, along with the lack of accompanying high - ionization state emission lines, suggest that these galaxies are young systems powered by star formation rather than by active galactic nucleus activity. Theoretical models of galaxy formation in the primordial universe suggest that a small fraction of Ly alpha-emitting galaxies at z approximate to 4.5 may still be nascent, metal-free objects. Indeed, we find with 90% confidence that three to five of the confirmed sources show W-lambda(rest) > 240 Angstrom, exceeding the maximum Lyalpha equivalent width predicted for normal stellar populations. Nonetheless, we find no evidence for He II lambda1640 emission in either individual or composite spectra, indicating that although these galaxies are young, they are not truly primitive, Population III objects.