SImulator of GAlaxy Millimetre/submillimetre Emission (sigame) CO emission from massive z 2 main sequence galaxies
We present SIGAME (SImulator of GAlaxy Millimetre/submillimetre Emission) a new numerical code designed to simulate the 12CO rotational line emission spectrum of galaxies. Using sub grid physics recipes to post process the outputs of smoothed particle hydrodynamics (SPH) simulations, a molecular gas phase is condensed out of the hot and partly ionized SPH gas. The gas is subjected to far UV radiation fields and cosmic ray ionization rates which are set to scale with the local star formation rate volume density. Level populations and radiative transport of the CO lines are solved with the 3 D radiative transfer code LIME. We have applied SIGAME to cosmological SPH simulations of three disc galaxies at z=2 with stellar masses in the range (0.5 2)x10^11 Msun and star formation rates ~40 140 Msun/yr. Global CO luminosities and line ratios are in agreement with observations of disc galaxies at z~2 up to and including J=3 2 but falling short of the few existing J=5 4 observations. The central 5 kpc regions of our galaxies have CO 3 2/1 0 and 7 6/1 0 brightness temperature ratios of ~0.55 0.65 and ~0.02 0.08, respectively, while further out in the disc the ratios drop to more quiescent values of ~0.5 and =3 and CO to H2 conversion factors =3.6 Msun*pc^2/(K km/s)