Astrochemistry

The Molecular Inventory of TMC-1 with GOTHAM Observations

By Keith Cowing

Status Report

astro-ph.GA

September 28, 2025

Filed under astro-ph.GA, astrochemistry, biochemistry, biosignature, GOTHAM, Interstellar, organic chemistry, Taurus Molecular Cloud (TMC 1)

The Molecular Inventory of TMC-1 with GOTHAM Observations — GOTHAM DRV observations and simulations. The top panel shows the calibrated observed spectra in black in K (left axis) and the noise level per channel in grey in mK (right axis). The receivers used in each frequency range are shown as colored bars. Data between 34250 and 35686 MHz in the Ka band are flagged due to abnormally high Tsys (see Appendix A for details). The bottom panel shows the simulated spectrum in red in K, generated from the MCMC fitting of 102 analyzed molecules. The absorption lines and some bright emission lines contributed by molecules that need special treatment are not included in the simulation. See the main text for details. — astro-ph.GA

Spectral line surveys of the Taurus Molecular Cloud-1 (TMC-1) have led to the detection of more than 100 new molecular species, making it the most prolific source of interstellar molecular discoveries.

These wide-band, high-sensitivity line surveys have been enabled by advances in telescope and receiver technology, particularly at centimeter and millimeter wavelengths. In this work, we present a statistical analysis of the molecular inventory of TMC-1 as probed by the GOTHAM large program survey from 3.9 to 36.4 GHz. To fully unlock the potential of the ∼29 GHz spectral bandwidth, we developed an automated pipeline for data reduction and calibration.

We applied a Bayesian approach with Markov-Chain Monte Carlo fitting to the calibrated spectra and constrained column densities for 102 molecular species detected in TMC-1, including 75 main isotopic species, 20 carbon-13 substituted species, and seven deuterium-substituted species.

This list of the detected gas-phase molecules is populated by unsaturated hydrocarbons, in stark contrast to the oxygen-rich organics found in sublimated ices around protostars. Of note, ten individual aromatic molecules were identified in the GOTHAM observations, contributing 0.011% of the gas-phase carbon budget probed by detected molecules when including CO and 6% when excluding CO.

This work provides a reference set of observed gas-phase molecular abundances for interstellar clouds, offering a new benchmark for astrochemical theoretical models.

Ci Xue, Alex N. Byrne, Larry Morgan, Gabi Wenzel, P. Bryan Changala, Zachary T.P. Fried, Ryan A. Loomis, Anthony Remijan, Edwin A. Bergin, Ilsa R. Cooke, David Frayer, Andrew M. Burkhardt, Steven B. Charnley, Martin A. Cordiner, Andrew Lipnicky, Michael C. McCarthy, Brett A. McGuire

Comments: Accepted for publication in The Astrophysical Journal Supplement Series. 12 tables, 9 figures, 1 figure set
Subjects: Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2509.06256 [astro-ph.GA] (or arXiv:2509.06256v1 [astro-ph.GA] for this version)
https://doi.org/10.48550/arXiv.2509.06256
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Submission history
From: Ci Xue
[v1] Mon, 8 Sep 2025 00:38:56 UTC (28,081 KB)
https://arxiv.org/abs/2509.06256

astrochemistry, astrobiology, astronomy,

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

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