Optical Spectroscopy and Nebular Oxygen Abundances of the Spitzer/SINGS Galaxies

• Published in: The Astrophysical journal. Supplement series Vol. 190; no. 2; pp. 233 - 266
• Main Authors: Moustakas, John, Kennicutt, Jr., Robert C, Tremonti, Christy A, Dale, Daniel A, Smith, John-David T, Calzetti, Daniela
• Format: Journal Article
• Language: English
• Published: United States IOP Publishing 01.10.2010
• Subjects: ABSORPTION SPECTROSCOPY; ABUNDANCE; ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ELEMENTS; EMISSION; GALAXIES; GALAXY NUCLEI; INFRARED SPECTRA; NONMETALS; ONE-DIMENSIONAL CALCULATIONS; OXYGEN; SPECTRA; SPECTROPHOTOMETRY; SPECTROSCOPY; STARS; TELESCOPES
• ISSN: 0067-0049; 1538-4365
• DOI: 10.1088/0067-0049/190/2/233

We present intermediate-resolution optical spectrophotometry of 65 galaxies obtained in support of the Spitzer Infrared Nearby Galaxies Survey (SINGS). For each galaxy we obtain a nuclear, circumnuclear, and semi-integrated optical spectrum designed to coincide spatially with mid- and far-infrared spectroscopy from the Spitzer Space Telescope. We make the reduced, spectrophotometrically calibrated one-dimensional spectra, as well as measurements of the fluxes and equivalent widths of the strong nebular emission lines, publically available. We use optical emission-line ratios measured on all three spatial scales to classify the sample into star-forming, active galactic nuclei (AGNs), and galaxies with a mixture of star formation and nuclear activity. We find that the relative fraction of the sample classified as star forming versus AGN is a strong function of the integrated light enclosed by the spectroscopic aperture. We supplement our observations with a large database of nebular emission-line measurements of individual H II regions in the SINGS galaxies culled from the literature. We use these ancillary data to conduct a detailed analysis of the radial abundance gradients and average H II-region abundances of a large fraction of the sample. We combine these results with our new integrated spectra to estimate the central and characteristic (globally averaged) gas-phase oxygen abundances of all 75 SINGS galaxies. We conclude with an in-depth discussion of the absolute uncertainty in the nebular oxygen abundance scale.