Star formation at z=1.47 from HiZELS: an Hα+[O II] double-blind study

This paper presents the results from the first wide and deep dual narrow-band survey to select Ha and [O ii] line emitters at z= 1.47 +/- 0.02, exploiting synergies between the United Kingdom Infrared Telescope and the Subaru telescope by using matched narrow-band filters in the H and z' bands. The Ha survey at z= 1.47 reaches a 3s flux limit of FHa similar to 7 x 10(-17) erg s-1 cm-2 (corresponding to a limiting star formation rate (SFR) in Ha of similar to 7 M yr(-1)) and detects similar to 200 Ha emitters over 0.7 deg2, while the much deeper [O ii] survey reaches an effective flux of similar to 7 x 10(-18) erg s-1 cm-2 (SFR in [O ii] of similar to 1 M yr(-1)), detecting approximate to 1400 z= 1.47 [O ii] emitters in a matched comoving volume of similar to 2.5 x 10(5) Mpc3. The combined survey results in the identification of 190 simultaneous Ha and [O ii] emitters at z= 1.47. Ha and [O ii] luminosity functions are derived and both are shown to evolve significantly from z similar to 0 in a consistent way. The SFR density of the Universe at z= 1.47 is evaluated, with the Ha analysis yielding SFR= 0.16 +/- 0.05 M yr(-1) Mpc-3 and the [O ii] analysis ?SFR= 0.17 +/- 0.04 M yr(-1) Mpc-3. The measurements are combined with other studies, providing a self-consistent measurement of the star formation history of the Universe over the last similar to 11 Gyr. By using a large comparison sample at z similar to 0.1, derived from the Sloan Digital Sky Survey (SDSS), [O ii]/Ha line ratios are calibrated as probes of dust extinction. Ha emitters at z similar to 1.47 show on average AHa similar to 1 mag, the same as found by SDSS in the local Universe. It is shown that although dust extinction correlates with SFR, the relation evolves by about similar to 0.5 mag from z similar to 1.5 to similar to 0, with local relations overpredicting the dust extinction corrections at high z by that amount. Stellar mass is found to be a much more fundamental extinction predictor, with the same relation between mass and dust extinction being valid at both z similar to 0 and similar to 1.5, at least for low and moderate stellar masses. The evolution in the extinctionSFR relation is therefore interpreted as being due to the evolution in median specific SFRs over cosmic time. Dust extinction corrections as a function of optical colours are also derived and shown to be broadly valid at both z similar to 0 and similar to 1.5, offering simpler mechanisms for estimating extinction in moderately star-forming systems over the last similar to 9 Gyr.