Studies in Molecular Astrophysics and Astrobiology

Licentiatavhandling, 2006

The molecules of the interstellar medium (ISM) can be used as probes of the physical conditions in a range of different types of interstellar environment, for example star forming regions. The first chapters of this thesis describe the theory and the observational techniques used to study the rotational transition emission from, and the present knowledge of, these molecules. In particular, models and observations of prebiotic molecules, like the simplest amino acid glycine, have become increasingly interesting in the light of a possible connection to the beginning of life on Earth. Searches for two prebiotic molecules, vinyl acetylene (C2H3 CCH) and amino acetonitrile (H2N CH2 CN), towards hot star-forming cores with the Onsala 20 metre radio telescope are presented. Neither of the molecules has been detected, but towards the richest molecular-line source observed, Orion KL, the upper column density limits are determined to N(C2H3 CCH)<1x1014 cm-2 and N(H2N CH2 CN)<2x1013 cm-2. In a comparison of the performance of the Odin1 sub-millimeter telescope and the Onsala 20 metre telescope, I show that the accuracy in intensities measured by Odin is considerably higher than for ground-based telescopes, in cases of extended sources. The 12CO and 13CO J=5-4 emissions have been mapped simultaneously in the Orion KL region using Odin. The CO J=5-4 narrow line emission from this region is shown to mainly arise in the warm, dense gas at the interface (the photon-dominated region) between the M42 HII region and the OMC1, where also previously mapped H2O emission has to originate. From the Odin CO data we determine the column density distribution of warm H2 gas across the mapped region, and estimate the ortho-water abundance in the Orion PDR layer to be >5x10-8. Footnote 1: 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 the Centre National d'Etudes Spatiales (CNES, France). The Swedish Space Corporation (SSC) was the industrial prime contractor and is also responsible for the satellite operation.