paper

Populating H $_{2}$ and CO in galaxy simulation with dust evolution

arXiv:1711.00600 · doi:10.1093/mnras/stx2863

Abstract

There are two major theoretical issues for the star formation law (the relation between the surface densities of molecular gas and star formation rate on a galaxy scale): (i) At low metallicity, it is not obvious that star-forming regions are rich in H $_{2}$ because the H $_{2}$ formation rate depends on the dust abundance; and (ii) whether or not CO really traces H $_{2}$ is uncertain, especially at low metallicity. To clarify these issues, we use a hydrodynamic simulation of an isolated disc galaxy with a spatial resolution of a few tens parsecs. The evolution of dust abundance and grain size distribution is treated consistently with the metal enrichment and the physical state of the interstellar medium. We compute the H $_{2}$ and CO abundances using a subgrid post-processing model based on the dust abundance and the dissociating radiation field calculated in the simulation. We find that when the metallicity is $≲ 0.4$ Z $_{⊙}$ ( $t < 1$ Gyr), H $_{2}$ is not a good tracer of star formation rate because H $_{2}$ -rich regions are limited to dense compact regions. At $Z ≳ 0.8$ Z $_{⊙}$ , a tight star formation law is established for both H $_{2}$ and CO. At old ( $t \sim 10$ Gyr) ages, we also find that adopting the so-called MRN grain size distribution with an appropriate dust-to-metal ratio over the entire disc gives reasonable estimates for the H $_{2}$ and CO abundances. For CO, improving the spatial resolution of the simulation is important while the H $_{2}$ abundance is not sensitive to sub-resolution structures at $Z ≳ 0.4$ Z $_{⊙}$ .

21 pages, 14 figures, accepted for publication in MNRAS

Populating H2​ and CO in galaxy simulation with dust evolution

Abstract

Populating H $_{2}$ and CO in galaxy simulation with dust evolution