Is the molecular KS relationship universal down to low metallicities?

TL;DR

This study uses high-resolution simulations to examine how metallicity and UV radiation influence star formation and the molecular Kennicutt-Schmidt relation in low-metallicity dwarf galaxies, finding minimal effects on star formation but a slight steepening of the relation at lower metallicities.

Contribution

First detailed simulation study of star formation and molecular gas relations in low-metallicity dwarf galaxies with varying UV fields, including non-equilibrium chemistry and sink particles.

Findings

Star formation rates are unaffected by a tenfold decrease in metallicity and UV field.

Cold gas depletion times are much longer than molecular gas depletion times.

The Kennicutt-Schmidt relation remains near linear at higher metallicity, steepening at lower metallicities.

Abstract

In recent years it has been speculated that in extreme low metallicity galactic environments, stars form in regions that lack H2. In this paper we investigate how changing the metallicity and UV-field strength of a galaxy affects the star formation within, and the molecular gas Kennicutt-Schmidt relation. Using extremely high resolution arepo simulations of isolated dwarf galaxies, we independently vary the metallicity and UV-field to between 1% and 10% solar neighbourhood values. We include a non-equilibrium, time-dependant chemical network to model the molecular composition of the ISM, and include the effects of gas shielding from an ambient UV field. Crucially our simulations directly model the gravitational collapse of gas into star-forming clumps and cores and their subsequent accretion using sink particles. In this first publication we find that reducing the metallicity and UV-field by a factor of 10 has no effect on star formation, and minimal effect on the cold, dense star forming gas. The cold gas depletion times are almost an order of magnitude longer than the molecular gas depletion time due to the presence of star formation in HI dominated cold gas. We study the H2 Kennicutt-Schmidt relationship that arises naturally within the simulations and find a near linear power law index of N = 1.09 +/- 0.014 in our fiducial 10% solar metallicity model. As the metallicity and UV-field are reduced this becomes moderately steeper, with a slope of N = 1.24 +/- 0.022 for our 1% solar metallicity and 1% solar UV field model.