A large Hα 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 H 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 2 deg 2 in the Cosmological Evolution Survey and Ultra Deep Survey fields. The deep multi-epoch H surveys reach a matched 3 flux limit of 3 M 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 H emitters. Catalogues are presented for a total of 1742, 637, 515 and 807 H emitters, robustly selected at z = 0.40, 0.84, 1.47 and 2.23, respectively, and used to determine the H luminosity function and its evolution. The faint-end slope of the H luminosity function is found to be = -1.60 0.08 over z = 0-2.23, showing no significant evolution. The characteristic luminosity of star-forming galaxies, L * H , evolves significantly as log L * H (z) = 0.45z + log L * z=0 . This is the first time H 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 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 0 to 2.2. Our uniform analysis allows us to derive the H star formation history (SFRH) of the Universe, showing a clear rise up to z 2.2, for which the simple parametrization log 10 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 H SFRH are consistent with the measurements of the stellar mass density growth, confirming that our H SFRH is tracing the bulk of the formation of stars in the Universe for z < 2.23. The star formation activity over the last 11 Gyr is responsible for producing 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 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.