Melanie Kaasinen

Melanie Kaasinen (Australia)

personal webpage

kaasinen @

The properties of the cold interstellar medium in high-redshift galaxies

Multiwavelength observations conducted over the last few decades have resulted in a consistent picture of the star formation history of the Universe.  The cosmic star formation rate density peaked after 3.5 gigayears (at z~2), and has since declined exponentially. To understand the declining cosmic star formation rate density, astronomers have looked to the source of star formation, the cold molecular phase of the interstellar medium. Current observations indicate an increase in the molecular gas mass relative to the stellar mass (gas fraction) up to z~2, matching the increase in the cosmic star formation rate density. However, the accuracy of gas masses derived at high redshift remains questionable.  
The aim of my PhD is to study the properties of the cold ISM in high-redshift galaxies and thereby improve the accuracy of the inferred gas masses. By simulating the emission from giant molecular clouds up to high redshifts I will investigate how the XCO conversion factor, used to derive molecular gass masses from CO luminosities, is affected by an increased contribution from the Cosmic Microwave Background.  I will also use observations of the CO J=1-0 emission in high redshift galaxies to investigate the accuracy of current methods of determining molecular gas masses and the effect of the many hidden assumptions currently used. My PhD will be shared between two institutes, the Institute for Theoretical Astronomy, where I will focus on simulating the cold ISM at different redshifts, and the Max Planck Institute for Astronomy, where I will analyse observations of the cold ISM at high redshifts.

Supervisors:  Fabian Walter  (MPIA), Simon Glover (ITA)

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