2013MNRAS.433.1567V

By combining high-resolution, radiative transfer cosmological simulations of z ~ 6 galaxies with a subgrid multiphase model of their interstellar medium, we derive the expected intensity of several far-infrared emission lines ([Cii] 158, [Oi] 63 and [Nii] 122 µm) for different values of the gas metallicity, Z. For Z = Z☉, the [Cii] spectrum is very complex due to the presence of several emitting clumps of individual sizes ≲ 3 kpc; the peak is displaced from the galaxy centre by ~100kms-1. While the [Oi] spectrum is also similarly displaced, the [Nii] line comes predominantly from the central ionized regions of the galaxy. When integrated over ∼ 500kms- 1, the [Cii] line flux is 185 mJykms- 1; 95 percent of such flux originates from the cold (T ~ 250 K) Hi phase and only 5 percent from the warm (T ~ 5000 K) neutral medium. The [Oi] and [Nii] fluxes are ∼ 6 and ∼ 90 times lower than the [Cii] one, respectively. By comparing our results with observations of Himiko, the most extended and luminous Lyman alpha emitter at z = 6.6, we find that the gas metallicity in this source must be subsolar. We conclude that the [Cii] line from z ~ 6 galaxies is detectable by the ALMA full array in 1.9 < tON < 7.7 h observing time, depending on Z.