April 2026
Estimating ionization fractions in SILCC simulations (Lennart Buhlmann)
THE CHARGE DISTRIBUTION OF DUST GRAINS IN THE INTERSTELLAR MEDIUM
Dust grains play a crucial role in the thermal, chemical and dynamic properties of the interstellar medium (ISM). For example, they are a catalyst for molecular hydrogen formation and more complex molecules, they are the main heating source of the cold and warm neutral medium through photoelectric heating, and they couple the interstellar magnetic field to the neutral gas within dense regions. Dust grains may be neutral, positively or negatively charged, and this charge regulates all their interactions with the ISM. In this project, we investigate the equilibrium charge distribution function of al dust grain population in various ISM environments, from the warm neutral medium, to the cold neutral and cold molecular medium, and derive a new set of parametric equations to reconstruct the charge distribution of a dust grain as a function of its size, composition and the properties of its environment.
Our model of the dust charge accounts for collisional charging by electrons and ions, photoelectric charging due to a background interstellar radiation field, the collection of suprathermal cosmic ray electrons and photoelectric emission due to a cosmic ray induced ultraviolet radiation field within dense molecular clouds. The charge distribution of dust grains is size and composition dependent, but it also depends on some properties of the environment such as local radiation field strength, temperature and electron density.
We find that in the molecular medium, both carbonaceous and silicate grains have mostly negative or neutral charges with narrow distributions. In the cold neutral medium, carbonaceous and silicate grains vary from negative and narrow distributions, to predominantly positive and wide distributions. In the warm neutral medium, grains of all sizes are positively charged with wide distributions.
Although we calculated the equilibrium charge distribution, i.e. assuming charging processes are much faster than the dynamics of the environment, we find that this condition holds for all of the environments studied here, and should even remain valid for simulations with very high resolution, down to AU scales. We have also derived a set of parametric equations that can be used to recover the charge distribution function of carbonaceous and silicate grains from 3.5 A to 0.25 μm, which can be easily implemented in chemical networks or numerical simulations where knowledge of the grain charge is necessary.
Monthly Highlights
March 2026
1D protostellar disk sub-grid model for star formation 3D MHD simulations (Anaïs Pauchet)
January 2026
Protostellar Outflows: From Simulations to Synthetic Observations (Taishi Ushirogi)
December 2025
Prestellar Core Formation in Colliding Gas Flows: Simulations and Synthetic Observations (Felix Rauprich)
November 2025
Measuring the Velocity Dispersion of the Warm Neutral Medium of the Milky Way at Galactic Scale using the Code FLASH (Wajdee Chayeb)
October 2025
Higher-order finite volume method for modelling shock waves in the interstellar medium (Mervin Yap)
June 2025
Simulating [CII] emission in high-redshift galaxies and their halos (Clarissa Immisch)
May 2025
Episodic Accretion onto Low Mass Protostars (Christian Riesop)
April 2025
Molecular cloud formation: Impact of metallicity, far-UV and CR heating using SILCC-Zoom simulations (Sanjit Pal)
March 2025
Modelling Protostellar Outflows in ISM Simulations (Michael Weis)
February 2025
Multi-band ray-tracing of ionizing photons (Sebastian Vider)
December 2024
Simulating the ISM and its processes (Sebastian Vider)