SDSS IV MaNGA - metallicity and nitrogen abundance gradients in local galaxies

Francesco Belfiore, Roberto Maiolino, Christy Tremonti, Sebastian F. Sánchez, Kevin Bundy, Matthew Bershady, Kyle Westfall, Lihwai Lin, Niv Drory, Médéric Boquien, Daniel Thomas, Jonathan Brinkmann

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Abstract

We study the gas phase metallicity (O/H) and nitrogen abundance gradients traced by star-forming regions in a representative sample of 550 nearby galaxies in the stellar mass range 109–1011.5 M⊙ with resolved spectroscopic data from the Sloan Digital Sky Survey IV Mapping Nearby Galaxies at Apache Point Observatory survey. Using strong-line ratio diagnostics (R23 and O3N2 for metallicity and N2O2 for N/O) and referencing to the effective (half-light) radius (Re), we find that the metallicity gradient steepens with stellar mass, lying roughly flat among galaxies with log (M⋆/M⊙) = 9.0 but exhibiting slopes as steep as −0.14 dex R−1eRe−1 at log (M⋆/M⊙) = 10.5 (using R23, but equivalent results are obtained using O3N2). At higher masses, these slopes remain typical in the outer regions of our sample (R > 1.5Re), but a flattening is observed in the central regions (R < 1Re). In the outer regions (R > 2.0Re), we detect a mild flattening of the metallicity gradient in stacked profiles, although with low significance. The N/O ratio gradient provides complementary constraints on the average chemical enrichment history. Unlike the oxygen abundance, the average N/O profiles do not flatten out in the central regions of massive galaxies. The metallicity and N/O profiles both depart significantly from an exponential form, suggesting a disconnect between chemical enrichment and stellar mass surface density on local scales. In the context of inside-out growth of discs, our findings suggest that central regions of massive galaxies today have evolved to an equilibrium metallicity, while the nitrogen abundance continues to increase as a consequence of delayed secondary nucleosynthetic production.
Original languageEnglish
Pages (from-to)151-170
Number of pages20
JournalMonthly Notices of the Royal Astronomical Society
Volume469
Issue number1
Early online date1 Apr 2017
DOIs
Publication statusPublished - 1 Jul 2017

Keywords

  • RCUK
  • STFC

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