Gabi Wenzel

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Carbon is synthesized in stars and processed continuously as matter cycles from stellar ejecta through molecular clouds and protoplanetary disks into planetary systems. Polycyclic aromatic hydrocarbons (PAHs) are thought to hold a significant fraction of this carbon, and their infrared emission features appear across galactic and extragalactic environments.
For decades, astronomers could /smell/ PAHs everywhere in space without being able to unambiguously identify a single one. Their broad infrared emission bands reflect a large molecular population rather than the fingerprint of any individual species. In this talk, I will show how laboratory spectroscopy and radio astronomy together have overcome this limitation. Every polar molecule has a unique rotational spectrum. We measure their spectra in the laboratory with chirped-pulse and cavity-enhanced Fourier-transform microwave spectroscopy, then search in sensitive radio surveys for molecular signal using spectral line stacking and matched filtering. In the cold molecular cloud TMC-1, this approach has revealed a growing family of aromatic molecules, including PAHs with up to seven fused rings, at abundances far exceeding model predictions. The detection of a three-ring PAH toward the protostellar core MC27/L1521F shows that these species persist as star formation begins.
These detections raise a central question: are these molecules built in cold clouds, or inherited from irradiated regions where PAHs are photoprocessed? I will conclude with an outlook on how cryogenic ion trap and photoprocessing experiments can address this, and provide the spectra needed for the next generation of targeted astronomical searches.

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MIT & CfA
H3
Contact: Stefanie Walch-Gassner