A Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE) XVII. Statistical properties of individual HII regions in unperturbed systems

TL;DR

This study analyzes the statistical properties of over 13,000 HII regions in unperturbed galaxies within the Virgo cluster, providing reference relations for star formation studies across different environments.

Contribution

It presents a comprehensive statistical analysis of HII regions in unperturbed systems, including luminosity functions and scaling relations, derived from deep narrow-band imaging data.

Findings

HII regions follow a Schechter luminosity function

Distribution of HII region sizes and densities characterized

Scaling relations between HII regions and host galaxy properties established

Abstract

The Virgo Environmental Survey Tracing Ionised Gas Emission (VESTIGE) is a blind narrow-band Halpha+[NII] imaging survey of the Virgo cluster carried out with MegaCam at the CFHT telescope. The survey provides deep narrow-band images for 385 galaxies hosting star forming HII regions. We identify individual HII regions and measure their main physical properties such as Halpha luminosity, equivalent diameter, and electron density with the purpose of deriving standard relations as reference for future local and high-z studies of HII regions in star forming systems in different environments. For this purpose we use a complete sample of ~ 13.000 HII regions of luminosity L(Halpha)>= 10^37 erg s^-1 to derive the main statistical properties of HII regions in unperturbed systems, identified as those galaxies with a normal HI gas content (64 objects). These are the composite Halpha luminosity function, equivalent diameter and electron density distribution, and luminosity-size relation. We also derive the main scaling relations between several parameters representative of the HII regions properties (total number, luminosity of the first ranked regions, fraction of the diffuse component, best fit parameters of the Schechter luminosity function measured for individual galaxies) and those characterising the properties of the host galaxies (stellar mass, star formation rate and specific star formation rate, stellar mass and star formation rate surface density, metallicity, molecular-to-atomic gas ratio, total gas-to-dust mass ratio). We briefly discuss the results of this analysis and their implications in the study of the star formation process in galaxy discs.