The star formation rate at redshift one: Hα spectroscopy with CIRPASS

We have conducted an Ha survey of 38 0.77 ≤ z ≤ 1 galaxies over ∼100 arcmin 2 of the Hubble Deep Field-North and Flanking Fields, to determine star formation rates (SFRs), with the near-IR multi-object spectrograph Cambridge Infrared Panoramic Survey Spectrograph (CIRPASS) on the William Herschel Telescope (WHT). This represents the first successful application of this technique to observing high-redshift galaxies. Stacking the spectra in the rest frame to infer a total SFR for the field, we find a lower limit (uncorrected for dust reddening) on the SFR density at redshift z = 1 of 0.04 M ⊙ yr -1 Mpc -3 . This implies rapid evolution in the SFR density from z = 0 to 1 which is proportional to (1 + z) 3.1 .