A. Stroe, D. Sobral

Abstract
We have carried out the largest (>3.5 × 10⁵ Mpc³, 26 deg²) Hα narrow-band survey to date at z ∼ 0.2 in the SA22, W2 and XMMLSS extragalactic fields. Our survey covers a large enough volume to overcome cosmic variance and to sample bright and rare Hα emitters up to an observed luminosity of ∼10^42.4 erg s⁻¹, equivalent to ∼11 M_⊙ yr⁻¹. Using our sample of 220 sources brighter than >10^41.4 erg s⁻¹ (>1 M_⊙ yr⁻¹), we derive Hα luminosity functions, which are well described by a Schechter function with ϕ★ = 10^{−2.85 ± 0.03} Mpc⁻³ and $// <![CDATA[ L^*_mathrm{Halpha } = 10^{41.71pm 0.02} // ]]>$  erg s⁻¹ (with a fixed faint end slope α = −1.35). We find that surveys probing smaller volumes (∼3 × 10⁴ Mpc³) are heavily affected by cosmic variance, which can lead to errors of over 100 per cent in the characteristic density and luminosity of the Hα luminosity function. We derive a star formation rate density of ρ_SFRD = 0.0094 ± 0.0008 M_⊙ yr⁻¹, in agreement with the redshift-dependent Hα parametrization from Sobral et al. The two-point correlation function is described by a single power law ω(θ) = (0.159 ± 0.012)θ^{(−0.75 ± 0.05)}, corresponding to a clustering length of r₀ = 3.3 ± 0.8 Mpc h⁻¹. We find that the most luminous Hα emitters at z ∼ 0.2 are more strongly clustered than the relatively fainter ones. The $// <![CDATA[ L^*_mathrm{Halpha } // ]]>$ Hα emitters at z ∼ 0.2 in our sample reside in ∼10^12.5−13.5 M_⊙ dark matter haloes. This implies that the most star-forming galaxies always reside in relatively massive haloes or group-like environments and that the typical host halo mass of star-forming galaxies is independent of redshift if scaled by $// <![CDATA[ L_mathrm{Halpha }/L^*_mathrm{Halpha }(z) // ]]>$ , as proposed by Sobral et al.

Keywords
galaxies: evolution - galaxies: formation - galaxies: luminosity function - mass function - large-scale structure of Universe

Monthly Notices of the Royal Astronomical Society
Volume 453, Issue 1, Page 242
2015 October

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