Far-infrared line emission from high-redshift galaxies

Abstract

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 ([C II] 158, [O I] 63 and [N II] 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 ≈100 km s-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 ~500 km s-1, the [CII] line flux is 185 mJy kms-1; 95 per cent of such flux originates from the cold (T ≈ 250 K) HI phase and only 5 per cent from the warm (T ≈ 5000 K) neutral medium. The [OI] and [N II] fluxes are ~6 and ~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 [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. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.