Abstract

We present deep rest-frame UV spectroscopic observations using the Gran Telescopio Canarias of six gravitationally lensed Ly alpha emitters (LAEs) at 2.36 z 2.82 selected from the BELLS GALLERY survey. By taking the magnifications into account, we show that LAEs can be as luminous as L-Ly alpha similar or equal to 30 x 10(42) erg s(-1) and M-UV similar or equal to -23 (AB) without invoking an AGN component, in contrast with previous findings. We measure Ly alpha rest-frame equivalent widths, EW0 (Ly alpha), ranging from 16 to 50 angstrom and Ly alpha escape fractions, f(esc) (Ly alpha), from 10 per cent to 40 per cent. Large EW0 (Ly alpha) and f(esc) (Ly alpha) are found predominantly in LAEs showing weak low-ionization ISM absorption (EW0 less than or similar to 1A) and narrow Ly alpha profiles (less than or similar to 300 km s(-1) FWHM) with their peak close (less than or similar to 80 km s(-1)) to their systemic redshifts, suggestive of less scatter from low HI column densities that favours the escape of Ly alpha photons. We infer stellar metallicities of Z/Z(circle dot) similar or equal to 0.2 in almost all LAEs by comparing the P-Cygni profiles of the wind lines NV1240 angstrom and C IV1549 angstrom with those from stellar synthesis models. We also find a trend between M-UV and the velocity offset of ISM absorption lines, such as the most luminous LAEs experience stronger outflows. The most luminous LAEs show star formation rates up to similar or equal to 180 M-circle dot yr(-1), yet they appear relatively blue (beta(UV) similar or equal to -1.8 to -2.0) showing evidence of little dust attenuation [E(B - V) = 0.10-0.14]. These luminous LAEs may be particular cases of young starburst galaxies that have had no time to form large amounts of dust. If so, they are ideal laboratories to study the early phase of massive star formation, stellar and dust mass growth, and chemical enrichment histories of starburst galaxies at high-z.