Recent observations have revealed the presence of strong CIII ] emission ( EW _ { CIII ] } > 20 Å ) in z > 6 galaxies , the origin of which remains unclear .
In an effort to understand the nature of these line emitters , we have initiated a survey targeting CIII ] emission in gravitationally-lensed reionization era analogs identified in HST imaging of clusters from the RELICS survey .
Here we report initial results on four galaxies selected to have low stellar masses ( 2-8 \times 10 ^ { 7 } M _ { \odot } ) and J _ { 125 } -band flux excesses indicative of intense [ OIII ] +H \beta emission ( EW _ { [ OIII ] + H \beta } =500-2000 Å ) , similar to what has been observed at z > 6 .
We detect CIII ] emission in three of the four sources , with the CIII ] EW reaching values seen in the reionization era ( EW _ { CIII ] } \simeq 17 - 22 Å ) in the two sources with the strongest optical line emission ( EW _ { [ OIII ] + H \beta } \simeq 2000 Å ) .
We have obtained a Magellan /FIRE near-infrared spectrum of the strongest CIII ] emitter in our sample , revealing gas that is both metal poor and highly ionized .
Using photoionization models , we are able to simultaneously reproduce the intense CIII ] and optical line emission for extremely young ( 2-3 Myr ) and metal poor ( 0.06-0.08 Z _ { \odot } ) stellar populations , as would be expected after a substantial upturn in the SFR of a low mass galaxy .
The sources in this survey are among the first for which CIII ] has been used as the primary means of redshift confirmation .
We suggest that it should be possible to extend this approach to z > 6 with current facilities , using CIII ] to measure redshifts of objects with IRAC excesses indicating EW _ { [ OIII ] + H \beta } \simeq 2000 Å , providing a method of spectroscopic confirmation independent of Ly \alpha .