Imprints of galaxy evolution on H ii regions Memory of the past uncovered by the CALIFA survey

TL;DR

This study analyzes ~5000 H ii regions from the CALIFA survey to understand how galaxy evolution influences their properties and positions in diagnostic diagrams, revealing that H ii regions retain a memory of past stellar and chemical evolution.

Contribution

It demonstrates that H ii regions' ionization conditions are affected by host galaxy properties and stellar populations, challenging purely photoionization model predictions.

Findings

H ii regions' line ratios depend on galaxy properties and location.

Their positions in diagnostic diagrams are influenced by underlying stellar populations.

H ii regions retain a memory of past stellar and chemical evolution.

Abstract

H ii regions in galaxies are the sites of star formation and thus particular places to understand the build-up of stellar mass in the universe. The line ratios of this ionized gas are frequently used to characterize the ionization conditions. We use the Hii regions catalogue from the CALIFA survey (~5000 H ii regions), to explore their distribution across the classical [OIII]/Hbeta vs. [NII]/Halpha diagnostic diagram, and how it depends on the oxygen abundance, ionization parameter, electron density, and dust attenuation. We compared the line ratios with predictions from photoionization models. Finally, we explore the dependences on the properties of the host galaxies, the location within those galaxies and the properties of the underlying stellar population. We found that the location within the BPT diagrams is not totally predicted by photoionization models. Indeed, it depends on the properties of the host galaxies, their galactocentric distances and the properties of the underlying stellar population. These results indicate that although H ii regions are short lived events, they are affected by the total underlying stellar population. One may say that H ii regions keep a memory of the stellar evolution and chemical enrichment that have left an imprint on the both the ionizing stellar population and the ionized gas