Molecular Astrophysics in Star-forming Regions with the Odin Satellite
Licentiate thesis, 2006
The interstellar medium is the cradle of life, stars and planets in the evolving Universe. Stars are born deep inside cold and dark molecular clouds, and affect the dynamical conditions in local regions by powerful winds, outflows, and by supernova explosions. Optical light from star-formation is trapped within the clouds because of absorption by dust grains. However, radiation is able to escape through the gas and dust in the infrared and radio spectral regions. In addition, the chemical evolution of molecules is very sensitive to temperature, density and radiation field. Thus, radio and submm observations of molecules are an excellent probe of both the physical and chemical conditions in star-forming regions and the interstellar medium in general.
Some important molecules are difficult to observe with ground-based telescopes due to the Earth's obscuring atmosphere. Hence observations from space are necessary in these spectral regions. The launch of the Odin* satellite in 2001, enabled observations of molecular oxygen and the ground-state water transition that traces shocks and star-formation.
One of the big unanswered questions in astronomy is the origin of structure. During the cosmic Dark Ages after the Big Bang, the Universe evolved from uniformity to the structures of galaxies, clusters, and voids that we observe today. Direct observations from the Dark Ages are most commonly believed to be impossible. But our aim in the search for the Primordial molecules is exactly this - to perform observations of resonant spectral lines from the cosmic Dark Ages.
To study the conditions in a star-forming region, including an unbiased search for new molecules, a spectral line survey has been performed toward the Orion KL massive star-forming region. We have observed 347 spectral lines from 38 molecules including isotopologues, while 19% of the lines remain unidentified. Six water lines are detected including the water isotopologues H217O, H218O and HDO. The total emission is dominated by CO, H2O, SO2, SO, 13CO and CH3OH. Species with the largest number of lines are CH3OH, (CH3)2O, SO2, 13CH3OH, CH3CN and NO.
*Odin is a Swedish-led satellite project funded jointly by the Swedish National Space Board (SNSB), the Canadian Space Agency (CSA), the National Technology Agency of Finland (Tekes) and Centre National d'Études Spatiales (CNES). The Swedish Space Corporation was the prime contractor and also is responsible for the satellite operation.