• Nagamine, Kentaro
• Hou, Kuan-Chou
• Chen, Li-Hsin
• Shimizu, Ikkoh
• Aoyama, Shohei

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<SUB>2</SUB> because the H<SUB>2</SUB> formation rate depends on the dust abundance; and (ii) whether or not CO really traces H<SUB>2</SUB> 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<SUB>2</SUB> 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<SUB>☉</SUB> (t &lt; 1 Gyr), H<SUB>2</SUB> is not a good tracer of star formation rate because H<SUB>2</SUB>-rich regions are limited to dense compact regions. At Z ≳ 0.8 Z<SUB>☉</SUB>, a tight star formation law is established for both H<SUB>2</SUB> and CO. At old (t ∼ 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<SUB>2</SUB> and CO abundances. For CO, improving the spatial resolution of the simulation is important, while the H<SUB>2</SUB> abundance is not sensitive to subresolution structures at Z ≳ 0.4 Z<SUB>☉</SUB>....

Topics

• impedance spectroscopy
• surface
• grain
• grain size
• simulation
• forming