A characteristic oxygen abundance gradient in galaxy disks unveiled with CALIFA^⋆,⋆⋆

¹ Instituto de Astrofísica de Andalucía (CSIC), Glorieta de la Astronomía s/n, Aptdo. 3004, 18080 Granada, Spain
e-mail: sanchez@iaa.es
² Centro Astronómico Hispano Alemán, Calar Alto, (CSIC-MPG), C/Jesús Durbán Remón 2-2, 04004 Almería, Spain
³ Instituto de Astronomía,Universidad Nacional Autonóma de Mexico, A.P. 70-264, 04510 México, D.F., México
⁴ Instituto Nacional de Astrofísica, Óptica y Electrónica, Luis E. Erro 1, 72840 Tonantzintla, Puebla Mexico
⁵ Departamento de Investigación Básica, CIEMAT, Avda. Complutense 40, 28040 Madrid, Spain
⁶ Instituto de Astrofísica de Canarias (IAC), 38205, La Laguna, Tenerife, Spain
⁷ 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
⁸ Departamento de Física Teórica, Universidad Autónoma de Madrid, 28049 Madrid, Spain
⁹ Departamento de Física, Universidade Federal de Santa Catarina, PO Box 476, 88040-900 Florianópolis, SC, Brazil
¹⁰ Depto. Astrofísica, Universidad de La Laguna (ULL), 38206, La Laguna, Tenerife, Spain
¹¹ School of Physics and Astronomy, University of St Andrews, North Haugh, St Andrews, KY16 9SS, UK
¹² CENTRA – Instituto Superior Tecnico, Av. Rovisco Pais 1, 1049-001 Lisbon, Portugal
¹³ Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
¹⁴ Astronomical Institute, Academy of Sciences of the Czech Republic, Boční II 1401/1a, 141 00 Prague, Czech Republic
¹⁵ Department of Theoretical Physics and Astrophysics, Faculty of Science, Masaryk University, Kotlářská 2, 611 37 Brno, Czech Republic
¹⁶ Max-Planck-Institut für Astronomie, Heidelberg, Germany
¹⁷ Sydney Institute for Astronomy, School of Physics A28, University of Sydney, Sydney, NSW 2006, Australia
¹⁸ Australian Astronomical Observatory, PO BOX 296, Epping, NSW 1710, Australia
¹⁹ Centro de Astrofísica and Faculdade de Ciencias, Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal

Received: 23 July 2013
Accepted: 28 November 2013

Abstract

We present the largest and most homogeneous catalog of H ii regions and associations compiled so far. The catalog comprises more than 7000 ionized regions, extracted from 306 galaxies observed by the CALIFA survey. We describe the procedures used to detect, select, and analyze the spectroscopic properties of these ionized regions. In the current study we focus on characterizing of the radial gradient of the oxygen abundance in the ionized gas, based on the study of the deprojecteddistribution of H ii regions. We found that all galaxies without clear evidence of an interaction present a common gradient in the oxygen abundance, with a characteristic slope of α_O/H = −0.1 dex/r_e between 0.3 and 2 disk effective radii (r_e), and a scatter compatible with random fluctuations around this value, when the gradient is normalized to the disk effective radius. The slope is independent of morphology, the incidence of bars, absolute magnitude, or mass. Only those galaxies with evidence of interactions and/or clear merging systems present a significantly shallower gradient, consistent with previous results. The majority of the 94 galaxies with H ii regions detected beyond two disk effective radii present a flattening in the oxygen abundance. The flattening is statistically significant. We cannot provide a conclusive answer regarding the origin of this flattening. However, our results indicate that its origin is most probably related to the secular evolution of galaxies. Finally, we find a drop/truncation of the oxygen abundance in the inner regions for 26 of the galaxies. All of them are non-interacting, mostly unbarred Sb/Sbc galaxies. This feature is associated with a central star-forming ring, which suggests that both features are produced by radial gas flows induced by resonance processes. Our result suggests that galaxy disks grow inside-out, with metal enrichment driven by the local star formation history and with a small variation galaxy-by-galaxy. At a certain galactocentric distance, the oxygen abundance seems to be correlated well with the stellar mass density and total stellar mass of the galaxies, independently of other properties of the galaxies. Other processes, such as radial mixing and inflows/outflows seem to have a limited effect on shaping of the radial distribution of oxygen abundances, although they are not ruled out.