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, SFE_mol, 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 (H_I perturbation). Analysis of the molecular- and the atomic-to-stellar mass ratios within R _e , ${R}_{\star }^{\mathrm{mol}}(r\lt {R}_{e})$ and ${R}_{\star }^{\mathrm{atom}}(r\lt {R}_{e})$ , shows that VERTICO galaxies have increasingly lower ${R}_{\star }^{\mathrm{atom}}(r\lt {R}_{e})$ for larger levels of H_I perturbation (compared to field galaxies matched in stellar mass), but no significant change in ${R}_{\star }^{{\rm{m}}{\rm{o}}{\rm{l}}}(r\lt {R}_{e})$ . We also measure a clear systematic decrease of the SFE_mol within R _e , SFE_mol(r < R_e ), 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.