GOTHAM — GBT Observations of TMC-1: Hunting Aromatic Molecules

GOTHAM is an extremely high-sensitivity (2 mK), high-resolution (0.02 km/s) spectral line survey of the cold core TMC-1 in X, K, and Ka bands. Pilot, targeted observations of the source over only <2 GHz of total bandwidth resulted in the detection of three new astronomical molecules, including the first radio detection of a benzene-ring aromatic (benzonitrile; C6H5CN), and of seven new isotopologues of carbon-chain species. The comparatively well-constrained homogeneous physical conditions of the source, in contrast to the canonical chemically rich Sgr B2(N) and Orion KL make it ideal for refining astrochemical models as uncertainties related to simulating physical conditions are minimized. In turn, these models can be used to derive astrophysical insight from astrochemical observations of these molecules in other sources. The GBT is the only instrument in the world capable of reaching the required level of sensitivity at the spectral resolution required by the extraordinarily narrow (0.1 km/s) spectral lines. To achieve these goals, we are therefore conducting a coordinated campaign involving observations, modeling, and laboratory analysis with a strong emphasis on providing the community with science-ready data products in the form of a fully-reduced spectral line survey.

Current Status

X-Band observations have been completed and were released publicly as part of Data Release 1 (DR1). These cover the range from 7900 – 11600 MHz. Data reduction details are presented in McGuire et al. 2020. These data are available from the journal or directly here (coming soon).

C- and S- band observations are completed, but suffer from heavy RFI. Data reduction is ongoing, with targeted completion in Fall 2022.

Ku-, KFPA, and Ka observations spanning ~13-35 GHz with a few gaps will be complete by August 2022. Data reduction observations already collected is ongoing, with a target to complete entire reduction in Fall 2022.

A public release of the entire survey is targeted for shortly after the final reduction is completed, hopefully very early 2023.


Initial data reduction is carried out using standard routines in GBTIDL, augmented to correct for the GBT’s inability to Doppler Track in each frequency window. Exceptionally fine control of Doppler Tracking corrections is necessary given the extremely narrow linewidths. Subsequent data reduction is carried out in Python. Details are presented in McGuire et al. 2020.

GOTHAM Publications

  • McGuire et al. 2020 ApJL 900, L10 (Overview, first detection of interstellar propargyl cyanide)
  • Xue et al. 2020 ApJL 900, L9 (First detection of interstellar HC4NC)
  • McGuire et al. 2021 Science 371, 1265 (First detection of the interstellar PAHs 1- and 2-cyanonaphthalene)
  • McCarthy et al. 2021 Nat. Astro. 5, 176 (First detection of 1-cyanocyclopentadiene)
  • Loomis et al. 2021 Nat. Astro. 5, 188 (Spectral stacking/filtering methodology; First detection of interstellar HC11N)
  • Burkhardt et al. 2021 Nat. Astro. 5, 181 (Detections of benzonitrile in many sources outside TMC-1)
  • Lee et al. 2021 ApJL 908, L11 (First detections of trans-cyanovinylacetylene and vinylcyanoacteylene)
  • Lee et al. 2021 ApJL 910, L2 (First detection of 2-cyanocyclopentadiene)
  • Burkhardt et al. 2021 ApJL 913, L18 (First detection of the PAH indene)
  • Shingledecker et al. 2021 A&AL 652, L12 (First detection of H2CCCHC3N)
  • Lee et al. 2021 ApJL 917, L6 (Machine learning approach to modeling chemical inventory of TMC-1)
  • Chitarra et al. 2021 A&A 652, A163 (A search for interstellar dicyanobenzene)
  • McCarthy & McGuire 2021 JPCA 125, 3231 (Aromatics and cyclic molecules in interstellar clouds review)
  • Barnum et al. 2021 ACS Earth & Space Chem. 5, 2986 (Search for furan in TMC-1)
  • Barnum et al. 2022 JPCA 126, 2716 (A search for heterocyclic molecules in TMC-1)
  • Siebert et al. 2022 ApJ 942, 21 (Detection of interstellar CH3C7N)

Team Members

PI: Brett A. McGuire (NRAO, CfA)

Andrew M. Burkhardt, Steven B. Charnley, Martin A. Cordiner, Eric Herbst, Sergei Kalenskii, Kin Long Kelvin Lee, Ryan A. Loomis, Michael C. McCarthy, Anthony J. Remijan, Christopher N. Shingledecker, Eric R. Willis, and Ci Xue.

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