We present Keck/MOSFIRE observations of UV metal lines in four bright ( H=23.9-25.4 ) gravitationally-lensed z \simeq 6 - 8 galaxies behind the cluster Abell 1703 .
The spectrum of A1703-zd6 , a highly-magnified star forming galaxy with a Ly \alpha redshift of z = 7.045 , reveals a confident ( S/N=5.1 ) detection of the nebular CIV \lambda 1548 emission line ( unresolved with FWHM < 125 km s ^ { -1 } ) .
UV metal lines are not detected in the three other galaxies .
At z \simeq 2 - 3 , nebular CIV emission is observed in just 1 % of UV-selected galaxies .
The presence of strong CIV emission in one of the small sample of galaxies targeted in this paper may indicate hard ionizing spectra are more common at z \simeq 7 .
The total estimated equivalent width of the CIV doublet ( W _ { CIV } \simeq 38 Å ) and CIV/Ly \alpha flux ratio ( f _ { CIV } /f _ { Ly \alpha } \simeq 0.3 ) are comparable to measurements of narrow-lined AGNs .
Photoionization models show that the nebular CIV line can also be reproduced by a young stellar population , with very hot metal poor stars dominating the photon flux responsible for triply ionizing carbon .
Regardless of the origin of the CIV , we show that the ionizing spectrum of A1703-zd6 is different from that of typical galaxies at z \simeq 2 , producing more H ionizing photons per unit 1500 Å luminosity ( { log ( \xi _ { ion } / erg ^ { -1 } } Hz ) =25.68 ) and a larger flux density at 30-50 eV .
If such extreme radiation fields are typical in UV-selected systems at z \mathrel { \hbox to 0.0 pt { \lower 4.0 pt \hbox { $ \sim$ } } \raise 1.0 pt \hbox { $ > $ } } 7 , it would indicate that reionization-era galaxies are more efficient ionizing agents than previously thought .
Alternatively , we suggest that the small sample of Ly \alpha emitters at z \mathrel { \hbox to 0.0 pt { \lower 4.0 pt \hbox { $ \sim$ } } \raise 1.0 pt \hbox { $ > $ } } 7 may trace a rare population with intense radiation fields capable of ionizing their surrounding hydrogen distribution .
Additional constraints on high ionization emission lines in galaxies with and without Ly \alpha detections will help clarify whether hard ionizing spectra are common in the reionization era .