HiZELS: a high-redshift survey of H alpha 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.