Zooming on the internal structure of z≃6 galaxies

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 × 1010 M, representative of a typical z ∼ 6 Lyman-break galaxy. Dahlia has a total H2 mass of 108. 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−1 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\ ₂\\, \ ₈₈\ 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 cm−3) 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.