The Abundance Scatter in M33 from HII Regions: Is There Any Evidence for
  Azimuthal Metallicity Variations?
  Optical spectra of 25 H II regions in the inner two kpc of the M33 disk have
been obtained with the GMOS spectrograph at the Gemini North telescope. The
oxygen abundance gradient measured from the detection of the [O III]4363
auroral line displays a scatter of approximately 0.06 dex, a much smaller value
than recently reported by Rosolowsky & Simon in this galaxy. The analysis of
the abundances for a large sample of H II regions derived from the R23
strong-line indicator confirms that the scatter is small over the full disk of
M33, consistent with the measuring uncertainties, and comparable to what is
observed in other spiral galaxies. No evidence is therefore found for
significant azimuthal variations in the present-day metallicity of the
interstellar medium in this galaxy on spatial scales from ~100 pc to a few kpc.
A considerable fraction of M33 H II regions with auroral line detections show
spectral features revealing sources of hard ionizing radiation (such as He II
emission and large [Ne III], [O III] line fluxes). Since R23 is shown to
severely underestimate the oxygen abundances in such cases, care must be taken
in chemical abundance studies of extragalactic H II regions based on this
strong-line indicator.
