The clustering of Hα emitters at z = 2.23 from HiZELS

Abstract

We present a clustering analysis of 370 high-confidence Hα 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 μm narrow-band survey using the United Kingdom Infrared Telescope Wide Field Camera (WFCAM). Averaging the two-point correlation function of HAEs in two ˜1° 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: ωHAE = b2ωDM 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 ΛCDM 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 ωDM 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.