The impact of bars on the properties of HII regions in the TIMER survey

TL;DR

This study analyzes how bars in galaxies influence the physical properties of HII regions, revealing significant differences based on location within barred galaxies, driven by bar-induced gas flows and galaxy mass.

Contribution

It provides the first detailed comparative analysis of HII region properties across different galaxy regions in a sample of barred galaxies, highlighting the impact of bars on ionized gas characteristics.

Findings

HII regions in the nuclear disc show extreme property values.

Galaxy mass correlates with higher HII region properties.

Bar presence influences gas concentration and HII region characteristics.

Abstract

In this study we perform a comparative analysis of the properties of the HII regions located in different areas of barred galaxies, with the aim of investigating the impact of bars on the physical properties of the ionised gas. Based on integral field spectroscopy data for 17 barred galaxies covering approximately the central 6x6 kpc, we detect a total of 2200 HII regions, of which 331 are located within the nuclear disc (also known as circumnuclear regions), 661 in the bar region, and 1208 in the disc. Among the physical properties of the HII regions, we explore the O/H and N/O abundances, H$\alpha$ luminosity, dust extinction, electron density, and H$\alpha$ equivalent width. We find clear differences in the properties of the HII regions between the nuclear disc, the bar and the disc, that could be explained by an enhancement in the molecular gas concentration in the central parts driven by bar-induced gas flows. As this gas is channelled towards the galaxy centre, the most extreme values in the analysed properties are found for the circumnuclear HII regions. Unlike the bar strength, galaxy mass does seem to affect the properties of the HII regions, with massive galaxies presenting higher values in most of the properties, possibly due to the increased amount of gas in these systems. This study provides evidence that the bar-driven redistribution of material within the galaxy inner parts causes significant differences in the HII region properties depending on their location within the galaxies.