A GBT Legacy Survey of Prebiotic Molecules Toward SgrB2(N-LMH)

Example: Understanding the Formation of Large Organic Molecules
Finally, why it is so important and advantageous to use the GBT? Over the last 2 years our team using the GBT has already detected 8 new interstellar molecules, a feat that is unequaled in such a short time by any other telescope or observing team in the history of molecular spectral line astronomy. Figure 5 shows those species we have detected toward SgrB2(N) with the GBT. From this graphical representation, it is possible to illustrate some of the chemical processes we believe are occurring in interstellar clouds that leads to the production of larger and larger interstellar species. First, successive hydrogen addition reactions account in the formation of ethylene glycol from glycolaldehyde which is the simplest possible aldehyde sugar. Successive hydrogen addition reactions also may account for the formation sequence of propYnal, propEnal, and propAnal and these species are important in the formation of amino acids. Oxygen addition accounts for the formation of cyclopropenone from cyclopropenylidene. Acetamide is one of two interstellar molecules with a peptide bond which is the way amino acids are polymerized into proteins. Acetamide can be formed in neutral radical reactions of the radicals CH2 or CH3 with formamide. Finally ketenimine can be isomerized from methyl formate by a process called tautomerization where the H atom migrates from the methyl group and finally attaches itself to the N. Because of the high activation barrier of some of these reactions, most of these reactions are probably powered by shocks in and surrounding the SgrB2(N) star-forming region.


Figure 5. Molecular Species that our team has detected using the GBT toward Sgr B2(N).

However, only through a systematic and complete spectral line survey, will it be possible to accurately constrain the formation mechanisms of these and even more complex molecular species.

Astrochemistry projects have been among the most productive research areas on the GBT, which has clearly demonstrated its unique power as a spectral line search instrument. The GBT beams are ideal for spatially widespread prebiotic species like we are finding now. Below 50 GHz, the GBT beams couple well to the extended molecular emission seen interstellar clouds. Because of the tremendous sensitivity, the GBT can reach an rms noise level of ~2 mK in two tracks on Sgr. Finally, the spectrometer is versatile and we have large spectral bandpasses with the existing equipment (e.g., 4x200 MHz = 24.4 kHz resolution). For all these reasons, the GBT is the only telescope currently in operation in the world that can be used for such a deep spectral line survey.