Maps and simulations of the nearby Milky Way

The 21-cm sky gives us velocity but not distance. This reconstruction separates nearby emission from distant Galactic structure and places the local atomic gas into a three-dimensional volume around the Sun.

This reconstruction combines my electron-density map with the Hutschenreuter et al. Faraday-rotation sky to infer how the line-of-sight magnetic field runs through the local volume. The animation follows samples from the posterior, showing both the recovered structure and where the reconstruction remains uncertain.

Using the Edenhofer 3D dust map and a census of nearby O stars, this simulation follows ionizing photons through the local ISM and predicts Hα, [S II], and [O III] emission. The lines respond differently to temperature and ionization, making it easier to compare where massive stars ionize gas and where recent supernova shocks affect the emission.

Stellar environment

The surrounding gas changes how far a star's photons travel

Ionizing luminosity is not the only factor. ζ Puppis and the Bajamar star emit nearly the same number of ionizing photons, but their environments give them very different reach. In this model, ζ Puppis influences a volume 827 times larger, showing how strongly a star's environment controls its impact on the wider ISM.

The same paper, followed through time

Birth cloud, H II region, supernova, remnant

A typical massive star first lights and disperses its birth cloud. Its supernova then flashes as an [O III]-bright shell, cools into [S II], and finally folds back into the turbulent interstellar medium.

Starting from a 3D dust map and the nearby O-star population, the model predicts the Hα sky from the Sun. Comparing the result with WHAM provides a check on how well the mapped gas and nearby stars reproduce the observed emission.

Oxygen does not move instantly between ionization states as the gas heats and cools. The result is an onion-skin structure around hot bubbles, with high ions surviving in thin gas long after a simple equilibrium model would erase them.

In low-density gas, recombination can take millions of years. Following that delay directly produces a stable, extended ionized layer; forcing the gas into equilibrium instead makes the layer flicker with the short lives of its stars.