Conversions between gas-phase metallicities in MaNGA
  We present polynomial conversions between each of 11 different strong line
gas-phase metallicity calibrations, each based on $\sim$ 1.1 million
star-forming spaxels in the public Sloan Digital Sky Survey (SDSS) Data Release
15 (DR15) Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey.
For this sample, which is $\sim$ 20 times larger than previous works, we
present 5th order polynomial fits for each of 110 possible calibration
conversions, for both Small Magellanic Cloud (SMC)-type and Milky Way (MW)-type
dust corrections. The typical $2\sigma$ scatter around our polynomial fits is
0.1 dex; we present the range over which the metallicities are valid.
Conversions between metallicities which rely on the same set of line ratios, or
a heavily shared set of emission lines, have reduced scatter in their
conversions relative to those conversions with little overlap in required
emission lines. Calibration conversions with less consistent sets of emission
lines also have increased galaxy-to-galaxy variability, and this variability
can account for up to 35% of the total scatter. We also compare our conversions
to previous work with the single fibre SDSS DR7 spectra along with higher
spatial resolution data from the TYPHOON Integral Field Spectroscopy survey,
resulting in comparison samples with spatial resolutions from several kpc down
to $\sim$100 pc. Our metallicity conversions, obtained with the large sample of
MaNGA, are robust against the influence of diffuse ionized gas, redshift,
effective radius and spatial blurring, and are therefore consistent across both
integrated spectra and the high resolution integral field spectroscopy data.
