O-bearing complex organic molecules at the cyanopolyyne peak of TMC-1: Detection of C 2 H 3 CHO, C 2 H 3 OH, HCOOCH 3 , and CH 3 OCH 3

We report the detection of the oxygen-bearing complex organic molecules propenal (C 2 H 3 CHO), vinyl alcohol (C 2 H 3 OH), methyl formate (HCOOCH 3 ), and dimethyl ether (CH 3 OCH 3 ) toward the cyanopolyyne peak of the starless core TMC-1. These molecules were detected through several emission lines in a deep Q -band line survey of TMC-1 carried out with the Yebes 40m telescope. These observations reveal that the cyanopolyyne peak of TMC-1, which is a prototype of a cold dark cloud rich in carbon chains, also contains O-bearing complex organic molecules such as HCOOCH 3 and CH 3 OCH 3 , which have previously been seen in a handful of cold interstellar clouds. In addition, this is the first secure detection of C 2 H 3 OH in space and the first time that C 2 H 3 CHO and C 2 H 3 OH have been detected in a cold environment, adding new pieces to the puzzle of complex organic molecules in cold sources. We derive column densities of (2.2 ± 0.3) × 10 11 cm −2 , (2.5 ± 0.5) × 10 12 cm −2 , (1.1 ± 0.2) × 10 12 cm −2 , and (2.5 ± 0.7) × 10 12 cm −2 for C 2 H 3 CHO, C 2 H 3 OH, HCOOCH 3 , and CH 3 OCH 3 , respectively. Interestingly, C 2 H 3 OH has an abundance similar to that of its well-known isomer acetaldehyde (CH 3 CHO), with C 2 H 3 OH/CH 3 CHO ∼ 1 at the cyanopolyyne peak. We discuss potential formation routes to these molecules and recognize that further experimental, theoretical, and astronomical studies are needed to elucidate the true formation mechanism of these O-bearing complex organic molecules in cold interstellar sources.