Mapping electron temperature variations across a spiral arm in NGC 1672

TL;DR

This study presents the first extragalactic measurements of electron temperature variations across a spiral arm in NGC 1672, revealing systematic temperature differences likely caused by azimuthal metallicity variations.

Contribution

It provides novel spatially-resolved electron temperature data across a spiral arm in a galaxy, linking temperature variations to azimuthal metallicity differences.

Findings

Electron temperature varies systematically across the spiral arm.

Temperature is lowest on the spiral arm and highest downstream.

Azimuthal metallicity variation is the most probable cause of temperature differences.

Abstract

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.