SÍGAME Simulations of the , , and Line Emission from Star-forming Galaxies at

Abstract

Of the almost 40 star-forming galaxies at (not counting quasi-stellar objects) observed in to date, nearly half are either very faint in or not detected at all, and fall well below expectations based on locally derived relations between star formation rate and luminosity. This has raised questions as to how reliable is as a tracer of star formation activity at these epochs and how factors such as metallicity might affect the emission. Combining cosmological zoom simulations of galaxies with SÍGAME (SImulator of GAlaxy Millimeter/submillimeter Emission), we modeled the multiphased interstellar medium (ISM) and its emission in , as well as in [O i ] and [O iii ], from 30 main-sequence galaxies at with star formation rates ∼3–23 , stellar masses , and metallicities . The simulations are able to reproduce the aforementioned faintness of some normal star-forming galaxy sources at . In terms of [O i ] and [O iii ], very few observations are available at , but our simulations match two of the three existing detections of [O iii ] and are furthermore roughly consistent with the [O i ] and [O iii ] luminosity relations with star formation rate observed for local starburst galaxies. We find that the emission is dominated by the diffuse ionized gas phase and molecular clouds, which on average contribute ∼66% and ∼27%, respectively. The molecular gas, which constitutes only of the total gas mass, is thus a more efficient emitter of than the ionized gas, which makes up ∼85% of the total gas mass. A principal component analysis shows that the luminosity correlates with the star formation activity of a galaxy as well as its average metallicity. The low metallicities of our simulations together with their low molecular gas mass fractions can account for their faintness, and we suggest that these factors may also be responsible for the -faint normal galaxies observed at these early epochs.