Outer-disk reddening and gas-phase metallicities: The CALIFA connection

¹ 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
e-mail: ramarino@ucm.es
² Department of Physics, Institute for Astronomy, ETH Zürich, 8093 Zürich, Switzerland
³ Departamento de Astrofísica y CC. de la Atmósfera, Facultad de CC. Físicas, Universidad Complutense de Madrid, Avda. Complutense s/n, 28040 Madrid, Spain
⁴ Instituto de Astronomía, Universidad Nacional Autonóma de México, A.P. 70-264, 04510 México, D. F., Mexico
⁵ Departamento de Física Teórica, Universidad Autónoma de Madrid, 28049 Madrid, Spain
⁶ Instituto de Física de Cantabria (CSIC -Universidad de Cantabria), Avenida de los Castros s/n, 39005 Santander, Spain
⁷ CIEMAT, Departamento de Investigación Básica, Avda. Complutense 40, 28040 Madrid, Spain
⁸ School of Physics and Astronomy, University of St Andrews, North Haugh, St. Andrews, KY16 9SS, UK ( SUPA )
⁹ Instituto Universitario Carlos I de Física Teórica y Computacional, Universidad de Granada, 18071 Granada, Spain
¹⁰ Departamento de Física Teórica y del Cosmos, Facultad de Ciencias, Universidad de Granada, 18071 Granada, Spain
¹¹ Instituto de Astrofísica de Andalucía (IAA/CSIC ), Glorieta de la Astronomía s/n Aptdo. 3004, 18080 Granada, Spain
¹² Australian Astronomical Observatory, PO Box 915, North Ryde, NSW 1670, Australia
¹³ Department of Physics and Astronomy, Macquarie University, NSW 2109, Australia
¹⁴ Millennium Institute of Astrophysics MAS, Nuncio Monseñor Sótero Sanz 100, Providencia, 7500011 Santiago, Chile
¹⁵ Departamento de Astronomía, Universidad de Chile, Camino El Observatorio 1515, Las Condes, Santiago, Chile
¹⁶ INAF–Osservatorio Astrofisico di Arcetri – Largo Enrico Fermi, 5 50125 Firenze, Italy
¹⁷ Department of Physics 4-181 CCIS, University of Alberta, Edmonton AB T6G 2E1, Canada
¹⁸ Instituto de Cosmologia, Relatividade e Astrofísica, Centro Brasileiro de Pesquisas Físicas, CEP 22290-180 Rio de Janeiro, Brazil
¹⁹ Estación Experimental de Zonas Aridas (CSIC), Carretera de Sacramento s/n, La Cañada, 04120 Almería, Spain
²⁰ Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, 4150-762 Porto, Portugal
²¹ Centro de Astrofísica da Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal
²² Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
²³ Sydney Institute for Astronomy, School of Physics A28, University of Sydney, NSW2006, Australia

Received: 17 July 2015
Accepted: 10 September 2015

Abstract

We study, for the first time in a statistically significant and well-defined sample, the relation between the outer-disk ionized-gas metallicity gradients and the presence of breaks in the surface brightness profiles of disk galaxies. Sloan Digital Sky Survey (SDSS) g′- and r′-band surface brightness, (g′ – r′) color, and ionized-gasoxygen abundance profiles for 324 galaxies within the Calar Alto Legacy Integral Field Area (CALIFA) survey are used for this purpose. We perform a detailed light-profile classification, finding that 84% of our disks show down- or up-bending profiles (Type II and Type III, respectively), while the remaining 16% are well fitted by one single exponential (Type I). The analysis of the color gradients at both sides of this break shows a U-shaped profile for most Type II galaxies with an average minimum (g′ − r′) color of ~0.5 mag and an ionized-gas metallicity flattening associated with it only in the case of low-mass galaxies. Comparatively, more massive systems show a rather uniform negative metallicity gradient. The correlation between metallicity flattening and stellar mass for these systems results in p-values as low as 0.01. Independent of the mechanism having shaped the outer light profiles of these galaxies, stellar migration or a previous episode of star formation in a shrinking star-forming disk, it is clear that the imprint in their ionized-gas metallicity was different for low- and high-mass Type II galaxies. In the case of Type III disks, a positive correlation between the change in color and abundance gradient is found (the null hypothesis is ruled out with a p-value of 0.02), with the outer disks of Type III galaxies with masses ≤10¹⁰ M_⊙ showing a weak color reddening or even a bluing. This is interpreted as primarily due to a mass downsizing effect on the population of Type III galaxies that recently experienced an enhanced inside-out growth.