![Schematic diagram of our spectral line stacking and matched filtering procedures. First, (a) shows relevant spectral regions of the (synthetic) observational data (black) and an initial spectral simulation (red). Each spectral window is then weighted based on the signal-to-noise ratio of each region to create a velocity stack of all relevant molecular rotational transitions (b). Finally, the stacked simulation is used as a matched filter and is cross-correlated with the stacked data to visualize the statistical significance of a given detection (c). -- [astro-ph.GA]](https://i0.wp.com/astrobiology.com/wp-content/uploads/2026/08/Exploring-the-Limits.png?fit=1200%2C679&ssl=1)
[astro-ph.GA] The formation history of polycyclic aromatic hydrocarbons (PAHs) in the interstellar medium remains a topic of active debate, with proposed mechanisms ranging from high-temperature stellar ejecta processes to low-temperature chemistry within molecular clouds.
Recently, the identification of small PAHs in the cold, dark cloud TMC-1 has provided some circumstantial evidence of the latter. If these are formed in situ, their isotopic ratios, particularly 12C/13C, should reflect the local, bulk material of the molecular cloud; in contrast, PAHs formed in the circumstellar envelopes of evolved stars may show enhanced 13C abundances.
The expected radio signals of these 13C substituted species will be faint, and thus we conducted a detailed proof-of-concept analysis examining whether spectral line stacking and matched filtering techniques can robustly retrieve signal from multiple singly substituted 13C isotopologues in aggregate.
We find that while retrieved signal decreases in the limit of spectral line confusion, false-positive detections are exceedingly improbable at the adopted 5σ matched filter response detection threshold. We then demonstrate the technique on actual observational data of isotopologues of HC9N toward TMC-1.
Finally, we show using synthetic data that if laboratory rotational spectra of all singly substituted 13C isotopologues of cyanonaphthalene and cyanopyrene isomers existed, current observations of TMC-1 would be sensitive enough to discriminate between a local, bulk 12C/13C ratio and one with an enhanced 13C abundance suggestive of inheritance.
Miya Duffy, Ryan A. Loomis, Martin S. Holdren, Andrew Lipnicky, D. Archie Stewart, Gabi Wenzel, Ci Xue, Annapoorani Hariharan, Ilsa R. Cooke, Anthony J. Remijan, Michael C. McCarthy, Brett A. McGuire
Subjects: Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2607.27382 [astro-ph.GA] (or arXiv:2607.27382v1 [astro-ph.GA] for this version)
https://doi.org/10.48550/arXiv.2607.27382
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Submission history
From: Miya Duffy
[v1] Wed, 29 Jul 2026 18:40:12 UTC (2,285 KB)
https://arxiv.org/abs/2607.27382
Astrobiology,
