We report new observations of SL2SJ021737-051329 , a lens system consisting of a bright arc at z = 1.84435 , magnified \sim 17 \times by a massive galaxy at z = 0.65 .
SL2SJ0217 is a low-mass ( M < 10 ^ { 9 } M _ { \odot } ) , low-metallicity ( Z \sim 1 / 20 Z _ { \odot } ) galaxy , with extreme star-forming conditions that produce strong nebular UV emission lines in the absence of any apparent outflows .
Here we present several notable features from rest-frame UV Keck/LRIS spectroscopy : ( 1 ) Very strong narrow emission lines are measured for C iv \lambda \lambda 1548,1550 , He ii \lambda 1640 , O iii ] \lambda \lambda 1661,1666 , Si iii ] \lambda \lambda 1883,1892 , and C iii ] \lambda \lambda 1907,1909 .
( 2 ) Double-peaked Ly \alpha emission is observed with a dominant blue peak and centered near the systemic velocity .
( 3 ) The low- and high-ionization absorption features indicate very little or no outflowing gas along the sightline to the lensed galaxy .
The relative emission line strengths can be reproduced with a very high-ionization , low-metallicity starburst with binaries , with the exception of He ii , which indicates an additional ionization source is needed .
We rule out large contributions from AGN and shocks to the photoionization budget , suggesting that the emission features requiring the hardest radiation field likely result from extreme stellar populations that are beyond the capabilities of current models .
Therefore , SL2S0217 serves as a template for the extreme conditions that are important for reionization and thought to be more common in the early Universe .