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

25 Sep 2015  ·  Marino R. A., de Paz A. Gil, Sánchez S. F., Sánchez-Blazquez P., Cardiel N., Castillo-Morales A., Pascual S., Vílchez J., Kehrig C., Mollá M., Mendez-Abreu J., Catalán-Torrecilla C., Florido E., Perez I., Ruiz-Lara T., Ellis S., López-Sánchez A. R., Delgado R. M. González, de Lorenzo-Cáceres A., García-Benito R., Galbany L., Zibetti S., Cortijo C., Kalinova V., Mast D., Iglesias-Páramo J., Papaderos P., Walcher C. J., Bland-Hawthorn J., Team the CALIFA ·

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. SDSS g'- and r'-band surface brightness, (g'- r') color, and ionized-gas oxygen abundance profiles for 324 galaxies within the 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 a ionized-gas metallicity flattening associated to it only in the case of low-mass galaxies. More massive systems show a rather uniform negative metallicity gradient. The correlation between metallicity flattening and stellar mass results in p-values as low as 0.01. Independently 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 $\leq$10$^{10}$ M$_{\odot}$ showing a weak color reddening or even a bluing. This is interpreted as primarily due to a mass down-sizing effect on the population of Type III galaxies having recently experienced an enhanced inside-out growth. read more

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