The metallicity dependence of the CO {\rightarrow} H_2 conversion factor in z>1 star forming galaxies

Understand

We use the first systematic samples of CO millimeter emission in z>1 'main-sequence' star forming galaxies (SFGs) to study the metallicity dependence of the conversion factor {\alpha}CO, from CO line luminosity to molecular gas mass.

• The molecular gas depletion rate inferred from the ratio of the star formation rate (SFR) to CO luminosity, is ~1 Gyr-1 for near-solar metallicity galaxies with stellar masses above M_S~1e11 M_sun.
• In this regime the depletion rate does not vary more than a factor of two to three as a function of molecular gas surface density, or redshift between z~0 and 2.
• Below M_S the depletion rate increases rapidly with decreasing metallicity.