2017MNRAS.465.2540P

We present zoom-in, adaptive mesh refinement, high-resolution (≃30 pc) simulations of high-redshift (z ≃ 6) galaxies with the aim of characterizing their internal properties and interstellar medium. Among other features, we adopt a star formation model based on a physically sound molecular hydrogen prescription, and introduce a novel scheme for supernova feedback, stellar winds and dust-mediated radiation pressure. In the zoom-in simulation, the target halo hosts 'Dahlia', a galaxy with a stellar mass M_* = 1.6 x 10¹⁰ M, representative of a typical z ∼ 6 Lyman-break galaxy. Dahlia has a total H₂ mass of 10^8.5 M that is mainly concentrated in a disc-like structure of effective radius ≃0.6 kpc and scale height ≃200 pc. Frequent mergers drive fresh gas towards the centre of the disc, sustaining a star formation rate per unit area of ≃15 M/yr kpc^–2. The disc is composed of dense (n >= 25 cm^–3), metal-rich (Z ≃ 0.5 Z_☉) gas that is pressure supported by radiation. We compute the 158 µm [C II] emission arising from Dahlia, and find that ≃95 per cent of the total [C II] luminosity (L_[C II]_ ~= 10^7.5 L_☉) arises from the H₂ disc. Although 30 per cent of the C II mass is transported out of the disc by outflows, such gas negligibly contributes to [C II] emission, due to its low density (n <= 10/cm3) and metallicity (Z <= 10^–1 Z_☉). Dahlia is underluminous with respect to the local [C II]-SFR relation; however, its luminosity is consistent with upper limits derived for most z ∼ 6 galaxies.