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Aperture effects on the oxygen abundance determinations from CALIFA data

J. Iglesias-Páramo, J. M. Vílchez, F. F. Rosales-Ortega, S. F. Sánchez, S. Duarte Puertas, V. Petropoulou, A. Gil de Paz, L. Galbany, M. Mollá, C. Catalán-Torrecilla, A. Castillo-Morales, D. Mast, B. Husemann, R. García-Benito, M. A. Mendoza, C. Kehrig, E. Pérez-Montero, P. Papaderos, J. M. Gomes, C. J. Walcher, R. M. González Delgado, R. A. Marino, Á. R. López-Sánchez, B. Ziegler, H. Flores, J. Alves


This paper aims at providing aperture corrections for emission lines in a sample of spiral galaxies from the Calar Alto Legacy Integral Field Area Survey (CALIFA) database. In particular, we explore the behavior of the log([OIII]λ5007/Hβ)/([NII]λ6583/Hα) (O3N2) and log[NII]λ6583/Hα (N2) flux ratios since they are closely connected to different empirical calibrations of the oxygen abundances in star forming galaxies. 
We compute median growth curves of Hα, Hα/Hβ, O3N2 and N2 up to 2.5R50 and 1.5 disk Reff. The growth curves simulate the effect of observing galaxies through apertures of varying radii. The median growth curve of the Hα/Hβ ratio monotonically decreases from the center towards larger radii, showing for small apertures a maximum value of ~10% larger than the integrated one. The median growth curve of N2 shows a similar behavior, decreasing from the center towards larger radii. No strong dependence is seen with the inclination, morphological type and stellar mass for these growth curves. Finally, the median growth curve of O3N2 increases monotonically with radius. However, at small radii it shows systematically higher values for galaxies of earlier morphological types and for high stellar mass galaxies. 
Applying our aperture corrections to a sample of galaxies from the SDSS survey at 0.02 ≤ z ≤ 0.3 shows that the average difference between fiber-based and aperture corrected oxygen abundances, for different galaxy stellar mass and redshift ranges, reaches typically to ~11%, depending on the abundance calibration used. This average difference is found to be systematically biased, though still within the typical uncertainties of oxygen abundances derived from empirical calibrations. Caution must be exercised when using observations of galaxies for small radii (e.g. below 0.5Reff) given the high dispersion shown around the median growth curves. Thus, the application of these median aperture corrections to derive abundances for individual galaxies is not recommended when their fluxes come from radii much smaller than either R50 or Reff.

galaxies: abundances, galaxies: general, galaxies: ISM

The Astrophysical Journal
Volume 826, Number 1
2016 July

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Faculdade de Ciências da Universidade de Lisboa Universidade do Porto Faculdade de Ciências e Tecnologia da Universidade de Coimbra
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia