VERTICO. IV. Environmental Effects on the Gas Distribution and Star Formation Efficiency of Virgo Cluster Spirals

We measure the molecular-to-atomic gas ratio, R mol, and the star formation rate (SFR) per unit molecular gas mass, SFEmol, in 38 nearby galaxies selected from the Virgo Environment Traced in CO (VERTICO) survey. We stack ALMA 12CO (J = 2−1) spectra coherently using H i velocities from the VIVA survey to detect faint CO emission out to galactocentric radii r gal ∼ 1.2 r 25. We determine the scale lengths for the molecular and stellar components, finding a ∼3:5 relation compared to ∼1:1 in field galaxies, indicating that the CO emission is more centrally concentrated than the stars. We compute R mol as a function of different physical quantities. While the spatially resolved R mol on average decreases with increasing radius, we find that the mean molecular-to-atomic gas ratio within the stellar effective radius R e , R mol(r < R e ), shows a systematic increase with the level of H i, truncation and/or asymmetry (HI perturbation). Analysis of the molecular- and the atomic-to-stellar mass ratios within R e , R ⋆ mol ( r < R e ) and R ⋆ atom ( r < R e ) , shows that VERTICO galaxies have increasingly lower R ⋆ atom ( r < R e ) for larger levels of HI perturbation (compared to field galaxies matched in stellar mass), but no significant change in R ⋆ m o l ( r < R e ) . We also measure a clear systematic decrease of the SFEmol within R e , SFEmol(r < Re ), with increasingly perturbed H i. Therefore, compared to field galaxies from the field, VERTICO galaxies are more compact in CO emission in relation to their stellar distribution, but increasingly perturbed atomic gas increases their R mol and decreases the efficiency with which their molecular gas forms stars.