The clustering of Hα emitters at ɀ=2.23 from HiZELS

Geach, J. E.; Sobral, D.; Hickox, R. C.; Wake, D. A.; Smail, Ian; Best, P. N.; Baugh, C. M. and Stott, J. P. (2012). The clustering of Hα emitters at ɀ=2.23 from HiZELS. Monthly Notices of the Royal Astronomical Society, 426(1) pp. 679–689.

DOI: https://doi.org/10.1111/j.1365-2966.2012.21725.x

Abstract

We present a clustering analysis of 370 high-confidence Hα emitters (HAEs) at ɀ = 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: ω_HAE = b²ω_DM where b = 2.4,sup>+0.1</sup>_-0.2. The corresponding ‘characteristic’ mass for the haloes hosting HAEs is log (M_h/[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 ω_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 M_h ≲ 10¹² h⁻¹ M_⊙ since ɀ ≈ 2, but with a broad occupation distribution and clustering that is likely to be a strong function of luminosity.

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