Imprints of galaxy evolution on H II regions

Memory of the past uncovered by the CALIFA survey^⋆

¹ Instituto de Astronomía, Universidad Nacional Autonóma de Mexico, A.P. 70-264, 04510 México, D.F., Mexico
e-mail: sanchez@iaa.es
² Instituto de Astrofísica de Andalucía (CSIC), Glorieta de la Astronomía s/n, Aptdo. 3004, 18080 Granada, Spain
³ Instituto Nacional de Astrofísica, Óptica y Electrónica, Luis E. Erro 1, 72840 Tonantzintla, Puebla, Mexico
⁴ Departamento de Física Teórica, Universidad Autónoma de Madrid, 28049 Madrid, Spain
⁵ Australian Astronomical Observatory, PO Box 915, North Ryde, Sydney, NSW 1670, Australia
⁶ Department of Physics and Astronomy, Macquarie University Sydney, NSW 2109, Australia
⁷ Centro Astronómico Hispano Alemán, Calar Al to, (CSIC-MPG), C/Jesús Durbán Remón 2-2, 04004 Almería, Spain
⁸ CEI Campus Moncloa, UCM-UPM, Departamento de Astrofísica y CC. de la Atmósfera, Facultad de CC. Físicas, Universidad Complutense de Madrid, Avda. Complutense s/n, 28040 Madrid, Spain
⁹ Dpto. de Física Teórica y del Cosmos, University of Granada, Facultad de Ciencias (Edificio Mecenas), 18071 Granada, Spain
¹⁰ Instituto de Cosmologia, Relatividade e Astrofísica – ICRA, Centro Brasileiro de Pesquisas Físicas, Rua Dr. Xavier Sigaud 150, CEP 22290-180 Rio de Janeiro, RJ, Brazil
¹¹ Centro de Astrofísica and Faculdade de Ciencias, Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal
¹² Sydney Institute for Astronomy, School of Physics A28, University of Sydney, Sydney, NSW 2006, Australia
¹³ Millennium Institute of Astrophysics, Universidad de Chile, Casilla 36-D, Santiago, Chile
¹⁴ Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile
¹⁵ GEPI, Observatoire de Paris, CNRS UMR 8111, Université Paris Diderot, Place Jules Janssen, 92190 Meudon, France
¹⁶ Departamento de Investigación Básica, CIEMAT, Avda. Complutense 40, 28040 Madrid, Spain
¹⁷ University of Vienna, Türkenschanzstrasse 17, 1180 Vienna, Austria
¹⁸ School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews, KY16 9SS, UK
¹⁹ Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
²⁰ Universität Heidelberg, Zentrum für Astronomie, Astronomisches Rechen Institut, Moenchhofstr. 12 – 14, 69120 Heidelberg, Germany
²¹ Astronomical Institute of the Ruhr-University Bochum Universitätsstr. 150, 44801 Bochum, Germany
²² Max-Planck-Institut für Astronomie, 69117 Heidelberg, Germany

Received: 28 August 2014
Accepted: 26 September 2014

Abstract

Context. H ii regions in galaxies are the sites of star formation, so they are special places for understanding the build-up of stellar mass in the universe. The line ratios of this ionized gas are frequently used to characterize the ionization conditions. In particular, the oxygen abundances are assumed to trace the chemical enrichment of galaxies.

Aims. We explore the connections between the ionization conditions and the properties of the overall underlying stellar population (ionizing or not-ionizing) in H ii regions, in order to uncover the actual physical connection between them.

Methods. We use the H ii regions catalog from the CALIFA survey, which is the largest in existence with more than 5000 H ii regions, to explore their distribution across the classical [O iii] λ5007/Hβ vs. [N ii] λ6583/Hα diagnostic diagram, and the way it depends on the oxygen abundance, ionization parameter, electron density, and dust attenuation. The location of H ii regions within this diagram is compared with predictions from photoionization models. Finally, we explore the dependence of the location within the diagnostic diagram on the properties of the host galaxies, the galactocentric distances, and the properties of the underlying stellar population.

Results. The H ii regions with weaker ionization strengths and more metal-rich are located in the bottom righthand area of the diagram. In contrast, those regions with stronger ionization strengths and more metal poor are located in the upper lefthand end of the diagram. Photoionization models per se do not predict these correlations between the parameters and the line ratios. The H ii regions located in earlier-type galaxies, closer to the center and formed in older and more metal-rich regions of the galaxies are located in the bottom-right area of the diagram. On the other hand, those regions located in late-type galaxies in the outer regions of the disks and formed on younger and more metal-poor regions lie in the top lefthand area of the diagram. The two explored line ratios show strong correlations with the age and metallicity of the underlying stellar population.

Conclusions. 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 both the ionizing stellar population and the ionized gas.