We present a detailed analysis of Hubble Space Telescope ( HST ) , Wide Field Camera 3 ( WFC3 ) G141 grism spectroscopy for seven star-forming regions of the highly magnified lensed starburst galaxy RCSGA 032727-132609 at z = 1.704 .
We measure the spatial variations of the extinction in RCS0327 through the observed H \gamma /H \beta emission line ratios , finding a constant average extinction of \mathrm { E ( B - V ) _ { gas } } = 0.40 \pm 0.07 .
We infer that the star formation is enhanced as a result of an ongoing interaction , with measured star formation rates derived from demagnified , extinction-corrected H \beta line fluxes for the individual star-forming clumps falling > 1–2 dex above the star formation sequence .
When combining the HST/WFC3 \mathrm { [ OIII ] } \lambda 5007 /H \beta emission line ratio measurements with [ NII ] /H \alpha line ratios from Wuyts et al .
( 103 ) , we find that the majority of the individual star-forming regions fall along the local “ normal ” abundance sequence .
With the first detections of the He I \lambda 5876 \mathrm { \AA } and He II \lambda 4686 \mathrm { \AA } recombination lines in a distant galaxy , we probe the massive-star content of the star-forming regions in RCS0327 .
The majority of the star-forming regions have a He I \lambda 5876 to H \beta ratio consistent with the saturated maximum value , which is only possible if they still contain hot O-stars .
Two regions have lower ratios , implying that their last burst of new star formation ended \sim 5 Myr ago .
Together , the He I \lambda 5876 \mathrm { \AA } and He II \lambda 4686 \mathrm { \AA } to H \beta line ratios provide indirect evidence for the order in which star formation is stopping in individual star-forming knots of this high redshift merger .
We place the spatial variations of the extinction , star formation rate and ionization conditions in the context of the star formation history of RCS0327 .