The clustering of Ha emitters at z=2.23 from HiZELS

We present a clustering analysis of 370 high-confidence Ha emitters (HAEs) at z = 2.23. The HAEs are detected in the Hi-Z Emission Line Survey (HiZELS), a large-area blank field 2.121 mu m narrow-band survey using the United Kingdom Infrared Telescope Wide Field Camera (WFCAM). Averaging the two-point correlation function of HAEs in two 1 degrees scale fields [United Kingdom Infrared Deep Sky Survey/Ultra Deep Survey (UDS) and Cosmological Evolution Survey (COSMOS) fields] we find a clustering amplitude equivalent to a correlation length of r0 = 3.7 +/- 0.3 h-1 Mpc for galaxies with star formation rates of 7 M yr-1. The data are also well-fitted by the expected correlation function of cold dark matter (CDM), scaled by a bias factor: HAE = b2 DM where b=2.4-0.2+0.1. The corresponding characteristic mass for the haloes hosting HAEs is log (Mh/[h-1 M ]) = 11.7 +/- 0.1. Comparing to the latest semi-analytic galform predictions for the evolution of HAEs in a CDM cosmology, we find broad agreement with the observations, with galform predicting an HAE correlation length of 4 h-1 Mpc. Motivated by this agreement, we exploit the simulations to construct a parametric model of the halo occupation distribution (HOD) of HAEs, and use this to fit the observed clustering. Our best-fitting HOD can adequately reproduce the observed angular clustering of HAEs, yielding an effective halo mass and bias in agreement with that derived from the scaled DM fit, but with the relatively small sample size the current data provide a poor constraint on the HOD. However, we argue that this approach provides interesting hints into the nature of the relationship between star-forming galaxies and the matter field, including insights into the efficiency of star formation in massive haloes. Our results support the broad picture that typical ( L ) star-forming galaxies have been hosted by dark matter haloes with Mh 1012 h-1 M since z 2, but with a broad occupation distribution and clustering that is likely to be a strong function of luminosity.