We investigate the potential for the emission lines OV ] \lambda \lambda 1213.8,1218.3 and HeII \lambda 1215.1 to contaminate flux measurements of Ly \alpha \lambda 1215.7 in the extended nebulae of quasars .
We have computed a grid of photoionization models with a substantial range in the slope of the ionizing powerlaw ( -1.5 < \alpha < -0.5 ) , gas metallicity ( 0.01 < Z / Z _ { \odot } < 3.0 ) , gas density ( 1 < n _ { H } < 10 ^ { 4 } cm ^ { -3 } ) , and ionization parameter ( 10 ^ { -5 } < U < 1.0 ) .
We find the contribution from HeII \lambda 1215.1 to be negligible , i.e. , < 0.1 of Ly \alpha flux , across our entire model grid .
The contribution from OV ] \lambda \lambda 1213.8,1218.3 is generally negligible when U is low ( \la 10 ^ { -3 } ) and/or when the gas metallicity is low ( Z / Z _ { \odot } \la 0.1 ) .
However , at higher values of U and Z we find that OV ] can significantly contaminate Ly \alpha , in some circumstances accounting for more than half the total flux of the Ly \alpha +HeII+OV ] blend .
We also provide means to estimate the fluxes of OV ] \lambda \lambda 1213.8,1218.3 and HeII \lambda 1215.1 by extrapolating from other lines .
We estimate the fluxes of OV ] and HeII for a sample of 107 Type 2 active galaxies at z > 2 , and find evidence for significant ( \geq 10 % ) contamination of Ly \alpha fluxes in the majority of cases ( 84 % ) .
We also discuss prospects for using OV ] \lambda \lambda 1213.8,1218.3 as a diagnostic for the presence of AGN activity in high-z Ly \alpha emitters , and caution that the presence of significant OV ] emission could impact the apparent kinematics of Ly \alpha , potentially mimicking the presence of high-velocity gas outflows .