Mapping electron temperature variations across a spiral arm in NGC 1672
  We report one of the first extragalactic observations of electron temperature
variations across a spiral arm. Using MUSE mosaic observations of the nearby
galaxy NGC 1672, we measure the [N II]5755 auroral line in a sample of 80 HII
regions in the eastern spiral arm of NGC1672. We discover systematic
temperature variations as a function of distance perpendicular to the spiral
arm. The electron temperature is lowest on the spiral arm itself and highest on
the downstream side. Photoionization models of different metallicity, pressure,
and age of the ionizing source are explored to understand what properties of
the interstellar medium drive the observed temperature variations. An
azimuthally varying metallicity appears to be the most likely cause of the
temperature variations. The electron temperature measurements solidify recent
discoveries of azimuthal variations of oxygen abundance based on strong lines,
and rule out the possibility that the abundance variations are artefacts of the
strong-line calibrations.
