A Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE). XXI. Statistical properties of individual HII regions in perturbed galaxies

TL;DR

This study analyzes the properties of HII regions in 385 Virgo cluster galaxies, revealing how environmental effects like ram pressure stripping influence star formation and gas distribution.

Contribution

It provides a detailed comparison of HII region properties between gas-deficient perturbed galaxies and unperturbed systems, highlighting environmental impact on galaxy evolution.

Findings

Perturbed galaxies have a steeper faint-end slope in luminosity functions.

Outer discs of gas-deficient galaxies show fewer HII regions.

Perturbed galaxies exhibit lower HII regions per unit stellar mass.

Abstract

We use narrow-band Halpha+[NII] imaging data gathered during VESTIGE, a blind survey of the Virgo cluster carried out with MegaCam at the CFHT, to identify HII regions in 385 galaxies showing ionised gas emission. We identify 76645 HII regions in 322 star-forming galaxies and study their physical properties for those above the completeness limit (L(Ha)>=10^37 erg s-1). The present work is focused on perturbed cluster galaxies, identified as those having a reduced amount of HI when compared to similar objects in the field. We derive composite luminosity functions, diameter and electron density distributions, and several scaling relations, and compare them to those already derived for gas-rich, unperturbed systems identified during the VESTIGE survey. The analysis shows that the statistical and physical properties of HI gas-deficient cluster galaxies are different from those of unperturbed systems, with perturbed objects having a steeper faint-end slope and a brighter characteristic Ha luminosity than gas-rich galaxies. The difference in the two distributions comes principally from the outer disc (outside the effective radius). The analysis of the scaling relations indicates that perturbed objects have a lower number of HII regions per unit stellar mass and disc surface than unperturbed systems, with differences increasing with the HI-deficiency parameter, principally in the outer disc where HII regions are less present in gas-poor systems. All these differences can be explained in the framework of galaxy evolution in rich environments, where their hydrodynamic interaction with the surrounding ICM (ram pressure) removes the gas outside-in quenching the star formation activity in the outer disc once the HI is removed.