Stellar and gaseous disc structures in cosmological galaxy equilibrium models

We present 'radially resolved equilibrium models' for the growth of stellar and gaseous discs in cosmologically accreting massive haloes. Our focus is on objects that evolve to redshifts z ~ 2. We solve the time-dependent equations that govern the radially dependent star formation rates, inflows and outflows from and to the inter- and circumgalactic medium, and inward radial gas flows within the discs. The stellar and gaseous discs reach equilibrium configurations on dynamical time-scales much shorter than variations in the cosmological dark matter halo growth and baryonic accretions rates. We show analytically that mass and global angular momentum conservation naturally give rise to exponential gas and stellar discs over many radial length-scales. As expected, the gaseous discs are more extended as set by the condition Toomre Q < 1 for star formation. The discs rapidly become baryon dominated. For massive, 5 × 10¹² M_⊙ haloes at redshift z = 2, we reproduced the typical observed star formation rates of ~100 M_⊙ yr^-1, stellar masses ~9 × 10¹⁰ M_⊙, gas contents ~10¹¹ M_⊙, half-mass sizes of 4.5 and 5.8 kpc for the stars and gas, and characteristic surface densities of 500 and 400 M_⊙ pc^-2 for the stars and gas.