We present an analysis of the star formation rate in galaxies between 0.7 < z < 1.8 using Near Infrared Camera and Multi-Object Spectrograph ( NICMOS ) grism spectral observations .
We detect 163 galaxies in an area of \sim 4.4 square arcminutes , 37 of which show possible H \alpha emission .
We extend the observed H \alpha luminosity function ( LF ) in this redshift range to luminosities a factor of two fainter than earlier work , and are consistent in the region of overlap .
Using the H \alpha LF , we estimate a star formation rate ( SFR ) density in this redshift range of 0.166 M _ { \odot } yr ^ { -1 } Mpc ^ { -3 } ( H _ { 0 } = 75 km s ^ { -1 } Mpc ^ { -1 } ) , consistent with other estimates based on emission lines , and supporting the order of magnitude increase in SFR density between z = 0 and z = 1 .
Our measurement of SFR density is a factor of \approx 2 - 3 greater than that estimated from UV data , comparable to the factor observed locally , implying little evolution in the relative extinctions between UV and H \alpha out to z \approx 1.3 .