H II regions are clouds of glowing, ionised gas associated with regions of recent star formation. By studying the light emitted by these regions, we can learn about their physical conditions and chemical composition, providing important clues about how stars and galaxies form and evolve.

One of the key properties we need to know is the temperature of the gas. We can measure it from the emission lines of different chemical elements, which probe different parts of an H II region. However, it is not always possible to measure all these temperatures directly. In these cases, we need to estimate them using relations between the temperatures measured from different elements.

In this work, using the DESIRED database, we analysed 699 spectra of H II regions and star-forming galaxies in the nearby Universe to study how these different temperatures are related. We found that some commonly used relations show considerable scatter, while those involving nitrogen provide more reliable estimates of the temperature in the low-ionisation regions of the gas.

These results help us identify which temperature relations are most reliable when observations are incomplete, improving our ability to determine the chemical composition of star-forming regions and galaxies.