Far-infrared line emission from high-redshift galaxies

By combining high-resolution, radiative transfer cosmological simulations of z approximate to 6 galaxies with a subgrid multiphase model of their interstellar medium, we derive the expected intensity of several far-infrared emission lines ([C ii] 158, [O i] 63 and [N ii] 122 mu m) for different values of the gas metallicity, Z. For Z = Z(circle dot), the [C ii] spectrum is very complex due to the presence of several emitting clumps of individual sizes less than or similar to 3 kpc; the peak is displaced from the galaxy centre by approximate to 100 km s(-1). While the [O i] spectrum is also similarly displaced, the [N ii] line comes predominantly from the central ionized regions of the galaxy. When integrated over similar to 500 km s(- 1), the [C ii] line flux is 185 mJy km s(- 1); 95 per cent of such flux originates from the cold (T approximate to 250 K) H i phase and only 5 per cent from the warm (T approximate to 5000 K) neutral medium. The [O i] and [N ii] fluxes are similar to 6 and similar to 90 times lower than the [C ii] 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 [C ii] line from z approximate to 6 galaxies is detectable by the ALMA full array in 1.9 < t(ON) < 7.7 h observing time, depending on Z.