PhD Defense by Vadim Rusakov

PhD Thesis: Link for the PhD Thesis will be updated, when it is uploaded by the NBI-Education team - PhD theses by DAWN – University of Copenhagen (

Title: Star Formation in Galaxies across Cosmic Time — Stellar Populations in Multiwavelength Photometric Observations


New observations of the James Webb Space Telescope (JWST) push the timeline of the universe to 2% of its present-day age and reveal that galaxies appear to be more evolved in the early universe than previously thought.  The brightest and most distant galaxies appear to produce more light or form sooner than expected from the physics of star formation in local galaxies or than predicted by the cosmological model.  By extension, models tuned in the later universe suggest that the early galaxies are also more massive than expected. 

This work addresses the problems of excessive stellar light and mass by investigating possible differences in the physics of star formation.  The so-called mass-to-light ratio is one of the fundamental properties of galaxies that connects star formation and the total amount of galaxy light.  Various case studies of stellar systems throughout the universe pointed to possible differences in the mass-to-light ratio compared to the standard models.  The study here implements some of these changes in the galaxy models and tests them using a large sample of images of distant galaxies in multiple wavelengths.  The findings show that active galaxies tend to form more massive stars in the past, and extrapolation of this effect can explain the unusually luminous objects observed with the JWST.  Therefore, modifications to the fundamental assumptions about star formation may be required.  Finally, this work also presents possible evidence of star formation in one of the most extreme environments in the universe — active galactic nuclei, which, if confirmed, can become one of the testing grounds for extreme conditions of star formation in the future.


  • Charles Steinhardt, Niels Bohr Institute, University of Copenhagen

Evaluation Committee:

  • Stephen Eales, Cardiff University
  • Christopher Conselice, University of Manchester
  • Lise Bech Christensen, Niels Bohr Institute, University of Copenhagen


There will be a following "lunch-reception" with bagel-sandwiches back at NBB in the DAWN Section on the 2nd floor (Niels Bohr Building, Rådmandsgade 62-64, 2200 Copenhagen N)