Bar effect on gas-phase abundance gradients. I. Data sample and chemical abundances
Studies of gas-phase radial metallicity profiles in spirals published in the last decade have diminished the importance of galactic bars as agents that mix and flatten the profiles, contradicting results obtained in the 1990s. We have collected a large sample of 2831 published H ii region emission-line fluxes in 51 nearby galaxies, including objects both with and without the presence of a bar, with the aim of revisiting the issue of whether bars affect the radial metal distribution in spirals. In this first paper of a series of two, we present the galaxy and the H ii region samples. The methodology is homogeneous for the whole data sample and includes the derivation of H ii region chemical abundances, structural parameters of bars and discs, galactocentric distances, and radial abundance profiles. We have obtained O/H and N/O abundance ratios from the Te-based (direct) method for a subsample of 610 regions, and from a variety of strong-line methods for the whole H ii region sample. The strong-line methods have been evaluated in relation to the Te-based one from both a comparison of the derived O/H and N/O abundances for individual H ii regions and a comparison of the abundance gradients derived from both methodologies. The median value and the standard deviation of the gradient distributions depend on the abundance method, and those based on the O3N2 indicator tend to flatten the steepest profiles, reducing the range of observed gradients. A detailed analysis and discussion of the derived O/H and N/O radial abundance gradients and y-intercepts for barred and unbarred galaxies is presented in the companion Paper II. The whole H ii region catalogue including emission-line fluxes, positions, and derived abundances is made publicly available on the CDS VizieR facility, together with the radial abundance gradients for all galaxies. © 2020 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society. ; We kindly thank all the authors who have previously published the HII data that form the basis for this work, and Simon Verley for his invaluable help with PYTHON. We also acknowledge the anonymous referee for his/her suggestions that improved the clarity of themanuscript. We thankCalar Alto Observatory for the allocation of director's discretionary time to this programme. AZ, EF, and IP acknowledge support from the Spanish 'Ministerio de Economia, Industria y Competitividad' (MINECO) and from the European Regional Development Fund (FEDER) via grant AYA2017-84897P, and from the Junta de Andalucia (Spain) local government through the FQM-108 project. EPM acknowledges funding from the Spanish MINECO project Estallidos 6 AYA2016-79724-C4 and from the Severo Ochoa excellence programme (SEV-20170709). This research made use of Astropy,15 a community-developed core PYTHON package for Astronomy (Astropy Collaboration 2013; Astropy Collaboration 2018); Matplotlib (Hunter 2007); APLpy, an open-source plotting package for PYTHON (Robitaille & Bressert 2012); NumPy (van der Walt et al. 2011) and seaborn (DOI:10.5281/zenodo.1313201). We acknowledge the usage of the HyperLeda database (http://leda.univ-lyon1.fr).This research has made use of the VizieR catalogue access tool, CDS, Strasbourg, France (DOI:10.26093/cds/vizier). The original description of the VizieR service was published in 2000, A&AS 143, 23. This research has made use of the NASA/IPAC Extragalactic Database (NED) that is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. ; Peer reviewed