Early Science from GOTHAM: Project Overview, Methods, and the Detection of Interstellar Propargyl Cyanide (HCCCH₂CN) in TMC-1

Abstract

We present an overview of the GBT Observations of TMC-1: Hunting Aromatic Molecules Large Program on the Green Bank Telescope. This and a related program were launched to explore the depth and breadth of aromatic chemistry in the interstellar medium at the earliest stages of star formation, following our earlier detection of benzonitrile (c-C6H5CN) in TMC-1. In this work, details of the observations, use of archival data, and data reduction strategies are provided. Using these observations, the interstellar detection of propargyl cyanide (HCCCH2CN) is described, as well as the accompanying laboratory spectroscopy. We discuss these results, and the survey project as a whole, in the context of investigating a previously unexplored reservoir of complex, gas-phase molecules in pre-stellar sources. A series of companion papers describe other new astronomical detections and analyses.

A study of C4H3N isomers in TMC-1: Line by line detection of HCCCH2CN

“…These lines are shown in Figs. 1 and species in space, recently claimed for the first time in TMC-1 by McGuire et al (2020) using the GBT. These authors presented a 5σ signal (18σ in the response impulse function) obtained by an intensity and noise-weighted average ('stack') of the data at the expected frequencies of the HCCCH 2 CN lines that could be present within the noise level.…”

“…Although most of the individual lines of HCCCH 2 CN are below the detection limit of the GBT data, four of them are detected at 1−3σ levels. Thanks to the high spectral resolution of these data (1.4 kHz), McGuire et al (2020) distinguished three cloud components in the line profiles (see Fossé et al 2001 for a detailed analysis of the velocity structure of this source).…”

“…rapid at low temperatures, something that was confirmed by Carty et al (2001), producing cyanoallene and the third C 4 H 3 N isomer: HCCCH 2 CN. This isomer was not detected in TMC-1 by Lovas et al (2006), although it was later found towards this same source during a centimetre line survey with the GBT (McGuire et al 2020). The detection of propargyl cyanide in TMC-1 by these authors relied on four individual lines detected at a modest signal-to-noise ratio (S/N) and was supported by the line stacking of 68 transitions.…”

Detection of interstellar H2CCCHC3N

“…Details of the observing strategy for these observations have been presented elsewhere (McGuire et al 2020(McGuire et al , 2018 and will only be summarized here. The spectral line survey data analyzed here were taken as part of the GOTHAM (GBT Observations of TMC-1: Hunting Aromatic Molecules) project using the 100 m Robert C. Byrd Green Bank Telescope (GBT; McGuire et al 2020). The full data set used includes observations from GBT projects GBT17A-164, GBT17A-434, GBT18A-333, and GBT18B-007 as well as data from project GBT19A-047 acquired through 2020 June.…”

Discovery of the propargyl radical (CH2CCH) in TMC-1: One of the most abundant radicals ever found and a key species for cyclization to benzene in cold dark clouds

“…The 40 m radiotelescope at Yebes Observatory is operated by the Spanish Geographic Institute (IGN, Ministerio de Transportes, Movilidad y Agenda Urbana). and C 5 H 3 N (Cernicharo et al 2021c,d;Marcelino et al 2021;McGuire et al 2020;Lee et al 2021), the five-membered ring C 5 H 5 CN (McCarthy et al 2020), and the aromatic ring C 6 H 5 CN (McGuire et al 2018;Burkhardt et al 2021). These detections reveal that there are chemical processes that are not yet well characterized, which are able to synthesize large complex organic molecules under very cold conditions.…”