Effective temperature of ionizing stars of extragalactic HII regions -- II: nebular parameter relations based on CALIFA data

TL;DR

This study analyzes the spatial variations of ionizing star temperatures, oxygen abundance, and ionization parameters in HII regions across 59 spiral galaxies using CALIFA data, revealing diverse gradient behaviors and their correlations.

Contribution

It provides the first comprehensive analysis of nebular parameter relations and their radial gradients in a large galaxy sample based on CALIFA data.

Findings

Most galaxies show positive $T_{eff}$ radial gradients.

Gradients of $ m log U$ and $T_{eff}$ depend on oxygen abundance gradients.

Galaxies with flat oxygen abundance gradients tend to have flat $T_{eff}$ and $ m log U$ gradients.

Abstract

We calculate the effective temperature ($T_{\rm eff}$) of ionizing star(s), oxygen abundance of the gas phase $(\rm O/H)$, and the ionization parameter $U$ for a sample of H\,{\sc ii} regions located in the disks of 59 spiral galaxies in the 0.005 < z < 0.03 redshift range. We use spectroscopic data taken from the CALIFA data release 3 (DR3) and theoretical (for $T_{\rm eff}$ and $U$) and empirical (for O/H) calibrations based on strong emission-lines. We consider spatial distribution and radial gradients of those parameters in each galactic disk for the objects in our sample. Most of the galaxies in our sample ($\sim70$ \%) shows positive $T_{\rm eff}$ radial gradients even though some them exhibit negative or flat ones. The median value of the $T_{\rm eff}$ radial gradient is 0.762 kK/$R_{25}$. We find that radial gradients of both $\log U$ and $T_{\rm eff}$ depend on the oxygen abundance gradient, in the sense that the gradient of $\log U$ increases as $\log(\rm O/H)$ gradient increases while there is an anti-correlation between the gradient of $T_{\rm eff}$ and the oxygen abundance gradient. Moreover, galaxies with flat oxygen abundance gradients tend to have flat $\log U$ and $T_{\rm eff}$ gradients as well. Although our results are in agreement with the idea of the existence of positive $T_{\rm eff}$ gradients along the disk of the majority of spiral galaxies, this seems not to be an universal property for these objects.