CO Emission, Molecular Gas, and Metallicity in Main-Sequence Star-Forming Galaxies at $z\sim2.3$

Understand

We present observations of CO(3-2) in 13 main-sequence $z=2.0-2.5$ star-forming galaxies at $\log(M_*/M_{\odot})=10.2-10.6$ that span a wide range in metallicity (O/H) based on rest-optical spectroscopy.

• We find that CO(3-2)/SFR decreases with decreasing metallicity, implying that the CO luminosity per unit gas mass is lower in low-metallicity galaxies at $z\sim2$.
• We constrain the CO-to-H$_2$ conversion factor ($\alpha_{\text{CO}}$) and find that $\alpha_{\text{CO}}$ inversely correlates with metallicity at $z\sim2$.
• We derive molecular gas masses ($M_{\text{mol}}$) and characterize the relations among $M_*$, SFR, $M_{\text{mol}}$, and metallicity.