The Impacts of Bars, Spirals, and Bulge Size on Gas-phase Metallicity Gradients in MaNGA Galaxies

Abstract

As galaxies evolve over time, the orbits of their constituent stars are expected to change in size and shape, moving stars away from their birth radius. Radial gas flows are also expected. Spiral arms and bars in galaxies are predicted to help drive this radial relocation, and it may be possible to trace this observationally, via a flattening of metallicity gradients. We use data from the Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey, part of the fourth phase of the Sloan Digital Sky Surveys (SDSS-IV), to look for correlations of the steepness of gas-phase metallicity gradients with various galaxy morphological features (e.g., the presence and pitch angle of spiral arms, the presence of a large scale bar, and bulge size). We select from MaNGA a sample of star-forming galaxies for which gas-phase metallicity trends can be measured and we use morphologies from the Galaxy Zoo survey. We observe that at fixed galaxy mass (1) the presence of spiral structure correlates with steeper gas-phase metallicity gradients; (2) spiral galaxies with larger bulges have both higher gas-phase metallicities and shallower gradients; (3) there is no observable difference in azimuthally averaged radial gradients between barred and unbarred spirals; and (4) there is no observable difference in gradient between tight and loosely wound spirals, but looser-wound spirals have lower average gas-phase metallicity values at fixed mass. We discuss the possible implications of these observational results.