A large H alpha survey at z=2.23, 1.47, 0.84 and 0.40: the 11 Gyr evolution of star-forming galaxies from HiZELS

This paper presents new deep and wide narrow-band surveys undertaken with United Kingdom Infrared Telescope (UKIRT), Subaru and the Very Large Telescope (VLT), a unique combined effort to select large, robust samples of Ha star-forming galaxies at z = 0.40, 0.84, 1.47 and 2.23 (corresponding to look-back times of 4.2, 7.0, 9.2 and 10.6 Gyr) in a uniform manner over similar to 2 deg(2) in the Cosmological Evolution Survey and Ultra Deep Survey fields. The deep multi-epoch Ha surveys reach a matched 3 sigma flux limit of approximate to 3 M-circle dot yr(-1) out to z = 2.2 for the first time, while the wide area and the coverage over two independent fields allow us to greatly overcome cosmic variance and assemble by far the largest samples of Ha emitters. Catalogues are presented for a total of 1742, 637, 515 and 807 Ha emitters, robustly selected at z = 0.40, 0.84, 1.47 and 2.23, respectively, and used to determine the H alpha luminosity function and its evolution. The faint-end slope of the Ha luminosity function is found to be alpha = -1.60 +/- 0.08 over z = 0-2.23, showing no significant evolution. The characteristic luminosity of star-forming galaxies, L*(H alpha), evolves significantly as log L*(H alpha) (z) = 0.45z + log L*(z=0). This is the first time H alpha has been used to trace star formation activity with a single homogeneous survey at z = 0.4-2.23. Overall, the evolution seen with H alpha is in good agreement with the evolution seen using inhomogeneous compilations of other tracers of star formation, such as far-infrared and ultraviolet, jointly pointing towards the bulk of the evolution in the last 11 Gyr being driven by a statistically similar star-forming population across cosmic time, but with a strong luminosity increase from z similar to 0 to similar to 2.2. Our uniform analysis allows us to derive the H alpha star formation history (SFRH) of the Universe, showing a clear rise up to z similar to 2.2, for which the simple parametrization log10 rho SFR = -2.1(1 + z)(-1) is valid over 80 per cent of the age of the Universe. The results reveal that both the shape and normalization of the Ha SFRH are consistent with the measurements of the stellar mass density growth, confirming that our Ha SFRH is tracing the bulk of the formation of stars in the Universe for z < 2.23. The star formation activity over the last similar to 11 Gyr is responsible for producing similar to 95 per cent of the total stellar mass density observed locally, with half of that being assembled in 2 Gyr between z = 1.2 and 2.2, and the other half in 8 Gyr (since z < 1.2). If the star formation rate density continues to decline with time in the same way as seen in the past similar to 11 Gyr, then the stellar mass density of the Universe will reach a maximum which is only 5 per cent higher than the present-day value.