HiZELS:: a high-redshift survey of Hα emitters -: I.: The cosmic star formation rate and clustering at z=2.23

We present results from a near-infrared narrow-band survey of emission-line galaxies at z = 2.23, using the Wide Field Camera on the United Kingdom Infrared Telescope. The H(2)S1 narrow-band filter (lambda(c) = 2.121 mu m) we employ selects the H alpha emission-line redshifted to z = 2.23, and is thus suitable for selecting 'typical' star-forming galaxies and active galactic nuclei at this epoch. The pilot study was undertaken in the well-studied Cosmological Evolution Survey field (COSMOS) and is already the largest near-infrared narrow-band survey at this depth, with a line flux limit of F-H alpha similar to 10(-16) erg s(-1) cm(-2) over 0.60 deg(2), probing similar to 220 x 10(3) Mpc(3) (comoving) down to a limiting star formation rate of similar to 30 M-circle dot yr(-1) (3 sigma). In this paper, we present the results from our pilot survey and evaluate the H alpha luminosity function and estimate the clustering properties of H alpha emitters at z = 2.23 from 55 detected galaxies. The integrated luminosity function is used to estimate the volume-averaged star formation rate at z = 2.23: rho(SFR) = 0.17(-0.09)(+0.16) M-circle dot yr(-1) Mpc(-3) for L-H alpha > 10(42) erg s(-1). For the first time, we use the H alpha star formation tracer to reliably constrain rho(SFR) out to z = 2.23 demonstrating the rapid increase in rho(SFR) out to this redshift as well as confirming the flattening in rho(SFR) between z similar to 1 and 2. In addition to the luminosity distribution, we analyse the clustering properties of these galaxies. Using the two-point angular correlation function, omega(theta), we estimate a real-space correlation length of r(0) = 4.2(-0.2)(+0.4) h(-1) Mpc. In comparison to models of clustering which take into account bias evolution, we estimate that these galaxies are hosted by dark matter haloes of mass M-halo similar to 10(12) M-circle dot consistent with the progenitors of the Milky Way.