Master Thesis defense by Ditlev Frickmann

Title: Investigating the morphologies of stars, gas and dust in starforming galaxies at cosmic noon

Abstract: We compare the morphologies of dust, molecular gas, and stars in 30 starforming galaxies at 0.5 ≲ z ≲ 3.5, selected from the Atacama Large Millimetre/submillimetre Array (ALMA) archive of CO, [CI] and [CII]. Using public photometric catalogues, we perform spectral energy distribution fitting to recover their stellar masses and star formation rates, and we classify 27 of the galaxies in our sample according to the main sequence relation at their respective redshifts. About 37% of our sample lie ≥ 0.6 dex above the mainsequence, and we classify them as starburst galaxies. We classify the remaining galaxies in our sample as main sequence galaxies. We analyse spatially resolved ALMA and Hubble Space Telescope (HST) data to study how the morphologies and sizes of our sample changes as a function of wavelength. We use subarcsecond ALMA observations of CO, [CI] and [CII] line emission to probe the molecular gas, and we extract the dust continua from the spectral cubes. We have auxiliary subarcsecond observations in restframe nearinfrared to nearultraviolet from HST, probing the stellar population. We find that the the gas line emission and dust continuum emission have similar spatial extents, which is consistent with the commonly adopted assumption that the dust continuum traces the underlying molecular gas. We find that the stellar emission is more extended than the gas line emission and the dust continuum by a factor of 1.61+1.04−0.72 and 1.61+0.55−0.43 respectively. However, we find that the relative extent of the stellar emission to that of the gas line emission is very sensitive to the gas conditions probed by the emission line. Specifically, we find that the stellar emission is more extended than the emission coming from CO(2-1) and CO(3-2) by a factor of 1.11+0.24−0.30 and 2.07+1.09−0.22 respectively. Finally, for the stellar emission, gas line emission and dust continuum, we find no systemic trends in the relative shape of the Sérsic surface brightness profiles with respect to their degree of central concentration, given by the Sérsic index.


  • Francesca Rizzo, University of Copenhagen, Niels Bohr Institute
  • Sune Toft, University of Copenhagen, Niels Bohr Institute


  • Allan Hornstrup, DTU Space