A Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE)

We used narrow-band H α +[N II ] imaging data gathered during the Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE) survey, a blind survey of the Virgo cluster carried out with MegaCam at the Canada-French-Hawaii telescope, to identify H II regions in 385 galaxies showing ionised gas emission. After excluding objects where the emission is not associated with star formation and edge-on systems, we identified 76 645 H II regions in 322 star-forming galaxies and studied their physical properties for those above the completeness limit of the survey ( L (H α ) ≥ 10 37 erg s −1 , 34 358 regions). The present work is focused on perturbed cluster galaxies, identified as those having a reduced amount of atomic hydrogen when compared to similar objects in the field. We derived composite luminosity functions, diameter and electron density distributions, and several scaling relations, and we compare them to those already derived for unperturbed gas-rich systems identified during the VESTIGE survey. Our analysis shows that the statistical and physical properties of H I gas-deficient cluster galaxies are different from those of unperturbed systems, with perturbed objects having a steeper faint-end slope and a brighter characteristic H α luminosity than gas-rich galaxies. The difference in the two distributions comes principally from the outer disc (outside the effective radius). Perturbed and unperturbed systems share a similar H II size distribution, while gas-poor objects host higher electron density regions than H I -rich systems. The analysis of the scaling relations indicates that perturbed objects have, on average, a lower number of H II regions per unit stellar mass and disc surface than unperturbed systems, with differences increasing with the H I -deficiency parameter, principally in the outer disc where H II regions are less present in gas-poor systems. This systematic difference is also observed in the H α luminosity of the first ranked and first three ranked H II regions, which is reduced in H I -deficient systems with respect to gas-rich objects. All of these differences can be explained in the framework of galaxy evolution in rich environments, where their hydrodynamic interaction with the surrounding intracluster medium (ram pressure) removes the gas from the outside in, quenching the star formation activity in the outer disc once the atomic hydrogen is removed.