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GBT Observations of TMC-1: Hunting Aromatic Molecules (GOTHAM)

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 are being prepared for Data Release 1 (DR1). These cover the range from 7900 – 11600 MHz. Data reduction details will be presented in McGuire et al. 2019a (in prep.).

K-band observations are at 53% completion, and cover the range from 22000 – 26100 MHz. Upon completion, these will likely comprise the bulk of DR2 (likely 2021).

Only pilot Ka-band observations have been conducted, with total survey coverage sitting at 6.2% completion. Current Ka-band projected coverage is 26100 – 33500 MHz. These will likely comprise the bulk of DR3 (likely 2023).

The timetables for DR2 and DR3 may be substantially shortened if daytime high-frequency observing is enabled by the forthcoming improvements to surface tracking on the GBT.


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 will be presented in McGuire et al. 2019a (in prep.).

GOTHAM Publications

  • McGuire et al. 2019a, in prep. (DR1 Paper)
  • McGuire et al. 2019b, in prep. (First detections of individual PAHs in the interstellar medium)
  • Loomis et al. 2019, in prep. (Detailed analysis procedures)
  • Xue et al. 2019, in prep. (Detection of a new cyanopolyyne isocyanide variant)
  • McCarthy et al. 2019, in prep. (Detection of the first 5-membered interstellar ring molecule)

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.