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A large narrow-band Hα survey at z∼ 0.2: the bright end of the luminosity function, cosmic variance and clustering across cosmic time

A. Stroe, D. Sobral

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 ∼1042.4 erg s−1, equivalent to ∼11 M yr−1. Using our sample of 220 sources brighter than >1041.4 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 LHα=1041.71±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 ρSFRD = 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 LHα Hα emitters at z ∼ 0.2 in our sample reside in ∼1012.5−13.5 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 LHα/LHα(z) , as proposed by Sobral et al.

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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Instituto de Astrofísica e Ciências do Espaço Universidade do Porto Faculdade de Ciências da Universidade de Lisboa Fundação para a Ciência e a Tecnologia
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