Bird's eye view of star formation in the local Milky Way - How perspective changes with scale, time and viewing angle

Doctoral thesis, 2023

A crucial aspect in interpreting the scaling relations relevant for star formation—the Kennicutt-Schmidt relation and the Larson relations—is how those relations depend on size-scale. This is especially so when comparing relations derived from unresolved, extragalactic data to those derived from resolved, Galactic data. We present an experiment in which the Solar neighbourhood (distance < 2 kpc) is examined from the outside, with an aim to unveil the connection between the true, “resolved” properties of star-forming regions and their beam-averaged, “unresolved” properties. To do so, we examine the density, velocity and star formation statistics of the dust and molecular gas in the Solar neighbourhood and determine how it appears when viewed through apertures of various sizes. First, we employ sub-pc resolution dust column density maps and star formation rates of individual molecular clouds from the literature to study the scale dependencies of molecular cloud structure from sub-pc to kpc scales. Second, we study a complete three dimensional volume of the Milky Way between the scales of ∼ 2−800 pc, taking advantage of three dimensional dust maps and young stars from recent advances made using Gaia satellite data. This second dataset gives the possibility to study not only the scale dependency of star formation, but also the dependence on age and orientation angle in the Milky Way. In these two ways, we connect the average properties of the gas in the local Galactic environment to the resolved properties at cloud scales. Our results provide observational constraints for star formation models. They can also aid the interpretation of on-going and upcoming extragalactic observations, especially by shedding light on the sub-beam properties of the structures detected by them.