Effects of dust evolution on the abundances of CO and H${}_2$

Abstract

The CO-to-H${}_2$ conversion factor ($X_{\mathrm{CO}}$) is known to correlate with the metallicity ($Z$). The dust abundance, which is related to the metallicity, is responsible for this correlation through dust shielding of dissociating photons and H${}_2$ formation on dust surfaces. In this paper, we investigate how the relation between dust-to-gas ratio and metallicity ($\mathcal{D}$--$Z$ relation) affects the H${}_2$ and CO abundances (and $X_{\mathrm{CO}}$) of a `molecular' cloud. For the $\mathcal{D}$--$Z$ relation, we adopt a dust evolution model developed in our previous work, which treats the evolution of not only dust abundance but also grain sizes in a galaxy. Shielding of dissociating photons and H${}_2$ formation on dust are solved consistently with the dust abundance and grain sizes. As a consequence, our models {predict consistent metallicity dependence of $X_{\mathrm{CO}}$ with observational data}. Among various processes driving dust evolution, grain growth by accretion has the largest impact on the $X_{\mathrm{CO}}$--$Z$ relation. The other processes also have some impacts on the $X_{\mathrm{CO}}$--$Z$ relation, but their effects are minor compared with the scatter of the observational data at the metallicity range ($Z\gtrsim 0.1$ Z${}_{\odot }$) where CO could be detected. We also find that dust condensation in stellar ejecta has a dramatic impact on the H${}_2$ abundance at low metallicities ($\lesssim 0.1$ Z${}_{\odot }$), relevant for damped Lyman $\alpha$ systems and nearby dwarf galaxies, and that the grain size dependence of H${}_2$ formation rate is also important.

18 pages, 7 figures, accepted for publication in MNRAS

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Cited by in corpus (7)

• Revealing the dust attenuation properties on resolved scales in NGC628 with SWIFT UVOT data
• Populating H${}_2$ and CO in galaxy simulation with dust evolution
• The co-evolution of molecular hydrogen and the grain size distribution in an isolated galaxy
• Beyond the Solar Circle $-$ Trends in Massive Star Formation Between the Inner and Outer Galaxy
• Effects of dust grain size distribution on the abundances of CO and H${}_2$ in galaxy evolution
• Effects of rotational disruption on the evolution of grain size distribution in galaxies
• CO-to-H${}_2$ conversion factor and grain size distribution through the analysis of ${\alpha }_{\mathrm{CO}}$-$q_{\mathrm{PAH}}$ relation