Revisiting the hardening of the stellar ionizing radiation in galaxy discs

DOI: 
10.1093/mnras/sty3330
Publication date: 
01/03/2019
Main author: 
Pérez-Montero, Enrique
IAA authors: 
Pérez-Montero, Enrique;García-Benito, Rubén;Vílchez, José M.
Authors: 
Pérez-Montero, Enrique;García-Benito, Rubén;Vílchez, José M.
Journal: 
Monthly Notices of the Royal Astronomical Society
Refereed: 
Yes
Publication type: 
Article
Volume: 
483
Pages: 
3322-3335
Abstract: 
In this work we explore accurate new ways to derive the ionization parameter (U) and the equivalent effective temperature (T<SUB>*</SUB>) in H II regions using emission-line intensities from the ionized gas. The so-called softness parameter (η), based on [O II], [O III], [S II], and [S III], has been proposed to estimate the hardening of the ionizing incident field of radiation, but the simplest relation of this parameter with T<SUB>*</SUB> also depends on U and metallicity (Z). Here we provide a Bayesian-like code (HCM-TEFF) that compares the observed emission lines of η with the predictions of a large grid of photoionization models giving precise estimations of both U and T<SUB>*</SUB> when Z is known. We also study the radial variation of these parameters in well-studied disc galaxies observed by the CHAOS collaboration. Our results indicate that the observed radial decreasing of η can be attributed to a radial hardening of T<SUB>*</SUB> across galactic discs as in NGC 628 and NGC 5457. On the other hand NGC 5194, which presents a positive slope of the fitting of the softness parameter, has a flat slope in T<SUB>*</SUB>. On the contrary the three galaxies do not seem to present large radial variations of the ionization parameter. When we inspect a larger sample of galaxies, we observe steeper radial variations of T<SUB>*</SUB> in less bright and later-type galaxies, mimicking a similar trend observed for Z, but the studied sample should be enlarged to obtain more statistically significant conclusions.
Database: 
ADS
SCOPUS
URL: 
https://www.scopus.com/inward/record.uri?eid=2-s2.0-85067197331&doi=10.1093%2fmnras%2fsty3330&partnerID=40&md5=5dc467bdd6446fc0c4d23ee7eb3cad04
ADS Bibcode: 
2019MNRAS.483.3322P
Keywords: 
methods: data analysis;ISM: abundances;galaxies: abundances;Astrophysics - Astrophysics of Galaxies