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

interstellar medium

star formation

Lecture room EA, EDIT building, Chalmers Johanneberg
Opponent: Prof. Clare Dobbs, University of Exeter, UK


Andri Spilker

Chalmers, Rymd-, geo- och miljövetenskap, Astronomi och plasmafysik

Bird's eye view of molecular clouds in the Milky Way: I. Column density and star formation from sub-pc to kpc scales

Astronomy and Astrophysics,; Vol. 653(2021)

Artikel i vetenskaplig tidskrift

The effect of viewing angle on the Kennicutt-Schmidt relation of the local molecular clouds

Astronomy and Astrophysics,; Vol. 659(2022)

Artikel i vetenskaplig tidskrift

Bird’s eye view of molecular clouds in the Milky Way: II. Cloud kinematics from subparsec to kiloparsec scales

Astronomy and Astrophysics,; Vol. 667(2022)

Artikel i vetenskaplig tidskrift

Spilker, A., Kainulainen, J., and Rezaei Kh., S. (subm). The volumetric Kennicutt-Schmidt relation in the local Milky Way: Model for the scale and age dependency. Submitted to Astronomy & Astrophysics.

Star formation involves a broad range of size-scales, and the physical phenomena across this entire range needs to be understood if we are to fully understand how much gas is converted into stars, how often stars form, and how massive they become. There is currently a gap in the size-scales that can be studied in our own and other galaxies. This thesis presents a new approach to bridging this gap and connecting studies of star formation in the Milky Way with other galaxies. The approach consists of assembling data for a complete sample of star forming gas in a large volume of the Milky Way. Recent advances in estimating distances to gas structures give the possibility to mimic how the region would look from the outside, in a bird’s-eye view. This way of viewing the star forming gas provides access to a wide range of scales, including the large scales accessible in other galaxies and the small scales accessible within the Milky Way. With this approach, we study gas and stars in a complete sample of the Milky Way disk. We study how the gas is distributed across high and low densities and velocities, how this connects to star formation, and how it depends on the studied scale. We also look into the three dimensional structure of the gas and how the relation of gas and stars evolves with time.


Astronomi, astrofysik och kosmologi

Annan fysik



Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5282



Lecture room EA, EDIT building, Chalmers Johanneberg


Opponent: Prof. Clare Dobbs, University of Exeter, UK

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