Zooming on the internal structure of z ≃ 6 galaxies

We present zoom-in, adaptive mesh refinement, high-resolution (similar or equal to 30 pc) simulations of highredshift (z similar to 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-star = 1.6 x 10(10)M(circle dot), representative of a typical z similar or equal to 6 Lyman-break galaxy. Dahlia has a total H-2 mass of 10(8.5)M(circle dot) that is mainly concentrated in a disc-like structure of effective radius similar to 0.6 kpc and scale height similar to 200 pc. Frequent mergers drive fresh gas towards the centre of the disc, sustaining a star formation rate per unit area of similar to 15M similar to yr(- 1) kpc(- 2). The disc is composed of dense (n similar to 25 cm(- 3)), metal- rich (Z similar to 0.5 Z similar to) gas that is pressure supported by radiation. We compute the 158 mu m [CII] emission arising from Dahlia, and find that similar to 95 per cent of the total [C II] luminosity (L[ C II] similar to 107.5 L similar to) 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 [CII] emission, due to its low density ( n similar to 10 cm- 3) and metallicity ( Z similar to 10(- 1) Z similar to). Dahlia is underluminous with respect to the local [C II]- SFR relation; however, its luminosity is consistent with upper limits derived for most z similar to 6 galaxies.