Star Formation in Galaxies between Redshifts of 0.7 and 1.8

We present an analysis of the star formation rate in galaxies with redshifts in the range 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 ∼4.4 arcmin2, 37 of which show possible Hα emission. We extend the observed Hα luminosity function (LF) in this redshift range to luminosities a factor of 2 fainter than earlier work and are consistent in the region of overlap. Using the Hα LF, we estimate a star formation rate (SFR) density in this redshift range of 0.166 M⊙ yr-1 Mpc-3 (H0 = 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 ≈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 Hα out to z ≈ 1.3.