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

Abstract

Abstract 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 12 CO ( 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 &lt; 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 , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mi>R</mml:mi> <mml:mo>⋆</mml:mo> <mml:mi>mol</mml:mi> </mml:msubsup> <mml:mo stretchy="false">(</mml:mo> <mml:mi>r</mml:mi> <mml:mo>&lt;</mml:mo> <mml:msub> <mml:mi>R</mml:mi> <mml:mi>e</mml:mi> </mml:msub> <mml:mo stretchy="false">)</mml:mo> </mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mi>R</mml:mi> <mml:mo>⋆</mml:mo> <mml:mi>atom</mml:mi> </mml:msubsup> <mml:mo stretchy="false">(</mml:mo> <mml:mi>r</mml:mi> <mml:mo>&lt;</mml:mo> <mml:msub> <mml:mi>R</mml:mi> <mml:mi>e</mml:mi> </mml:msub> <mml:mo stretchy="false">)</mml:mo> </mml:math> , shows that VERTICO galaxies have increasingly lower <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mi>R</mml:mi> <mml:mo>⋆</mml:mo> <mml:mi>atom</mml:mi> </mml:msubsup> <mml:mo stretchy="false">(</mml:mo> <mml:mi>r</mml:mi> <mml:mo>&lt;</mml:mo> <mml:msub> <mml:mi>R</mml:mi> <mml:mi>e</mml:mi> </mml:msub> <mml:mo stretchy="false">)</mml:mo> </mml:math> for larger levels of H I perturbation (compared to field galaxies matched in stellar mass), but no significant change in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mi>R</mml:mi> <mml:mrow> <mml:mo>⋆</mml:mo> </mml:mrow> <mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">m</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">o</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">l</mml:mi> </mml:mrow> </mml:mrow> </mml:msubsup> <mml:mo stretchy="false">(</mml:mo> <mml:mi>r</mml:mi> <mml:mo>&lt;</mml:mo> <mml:msub> <mml:mi>R</mml:mi> <mml:mi>e</mml:mi> </mml:msub> <mml:mo stretchy="false">)</mml:mo> </mml:math> . We also measure a clear systematic decrease of the SFE mol within R e , SFE mol ( r &lt; 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.