Electron temperature relations in low metallicity, diffuse, and extraplanar gas of starburst galaxies

In this work, we test the validity of Te - Te relations in resolved (10-200 pc) measurements of four nearby, low-metallicity (7.25 ≤ 12+log(O/H) ≤ 8.33), low-mass (106.78 ≤ M*/M⊙ ≤ 108.7), starburst (10−4.5 ≤ sSFR ≤ 10−0.3) galaxies. We obtain VLT/X-Shooter spectra of NGC 5253, NGC 0625, SBS 0335-052E and IC 2828, targeting regions within these galaxies with bright point-like sources and diffuse gas. Our observations are designed to extend from the galaxy midplane into extraplanar gas likely belonging to galactic winds. We measure electron temperatures from five different auroral lines: [N ii] λ5755, [O ii] λλ7319,30, [S ii] λλ4069,76, [S iii] λ6312, and [O iii] λ4363. We compare the resulting Te - Te relations with previous studies of H ii regions in nearby spiral galaxies. Our results show that Te - Te relations in low-metallicity starburst galaxies do not significantly deviate from Te - Te relations in H ii regions of local spiral galaxies. We do not find significant differences in the diffuse, extraplanar gas. These results suggest that auroral lines provide a reliable metallicity diagnostic not only for high-redshift galaxies but also for the extended diffuse gas in extreme environments like outflows.