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A large narrow band H$α$ survey at $z\sim0.2$: the bright end of the luminosity function, cosmic variance and clustering across cosmic time (1507.02687v1)

Published 9 Jul 2015 in astro-ph.GA

Abstract: We carried out the largest ($>3.5\times105$ Mpc$3$, 26 deg$2$) H$\alpha$ narrow band survey to date at $z\sim0.2$ 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 H$\alpha$ emitters up to an observed luminosity of $\sim10{42.4}$ erg s${-1}$, equivalent to $\sim11 M_\odot$ yr${-1}$. Using our sample of $220$ sources brighter than $>10{41.4}$ erg s${-1}$ ($>1 M_\odot$ yr${-1}$), we derive H$\alpha$ luminosity functions, which are well described by a Schechter function with $\phi* = 10{-2.85\pm0.03}$ Mpc${-3}$ and $L*_{H\alpha} = 10{41.71\pm0.02}$ erg s${-1}$ (with a fixed faint end slope $\alpha=-1.35$). We find that surveys probing smaller volumes ($\sim3\times104$ Mpc$3$) are heavily affected by cosmic variance, which can lead to errors of over $100$ per cent in the characteristic density and luminosity of the H$\alpha$ luminosity function. We derive a star formation rate density of $\rho_\mathrm{SFRD} = 0.0094\pm0.0008$ $M_\odot$ yr${-1}$, in agreement with the redshift-dependent H$\alpha$ parametrisation from Sobral et al. (2013). The two-point correlation function is described by a single power law $\omega(\theta) = (0.159\pm0.012) \theta{(-0.75\pm0.05)}$, corresponding to a clustering length of $r_0 = 3.3\pm0.8$ Mpc/h. We find that the most luminous H$\alpha$ emitters at $z\sim0.2$ are more strongly clustered than the relatively fainter ones. The $L*_{H\alpha}$ H$\alpha$ emitters at $z\sim0.2$ in our sample reside in $\sim10{12.5-13.5}$ $M_\odot$ 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 $L_\mathrm{H\alpha}/L*_{H\alpha}(z)$, as proposed by Sobral et al. (2010).

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