A&A 649, L4 (2021) Astronomy https://doi.org/10.1051/0004-6361/202140978 & c ESO 2021 Astrophysics LETTER TO THE EDITOR O-bearing complex organic molecules at the cyanopolyyne peak of ? TMC-1: Detection of C2H3CHO, C2H3OH, HCOOCH3, and CH3OCH3 M. Agúndez1, N. Marcelino1, B. Tercero2,3, C. Cabezas1, P. de Vicente3, and J. Cernicharo1 1 Instituto de Física Fundamental, CSIC, Calle Serrano 123, 28006 Madrid, Spain e-mail: [email protected] 2 Observatorio Astronómico Nacional, IGN, Calle Alfonso XII 3, 28014 Madrid, Spain 3 Observatorio de Yebes, IGN, Cerro de la Palera s/n, 19141 Yebes, Guadalajara, Spain Received 1 April 2021 / Accepted 21 April 2021 ABSTRACT We report the detection of the oxygen-bearing complex organic molecules propenal (C2H3CHO), vinyl alcohol (C2H3OH), methyl formate (HCOOCH3), and dimethyl ether (CH3OCH3) 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 HCOOCH3 and CH3OCH3, which have previously been seen in a handful of cold interstellar clouds. In addition, this is the first secure detection of C2H3OH in space and the first time that C2H3CHO and C2H3OH have been detected in a cold environment, adding new pieces to the puzzle of complex organic molecules in cold sources. We derive 11 −2 12 −2 12 −2 12 −2 column densities of (2.2 ± 0.3) × 10 cm , (2.5 ± 0.5) × 10 cm , (1.1 ± 0.2) × 10 cm , and (2.5 ± 0.7) × 10 cm for C2H3CHO, C2H3OH, HCOOCH3, and CH3OCH3, respectively. Interestingly, C2H3OH has an abundance similar to that of its well-known isomer acetaldehyde (CH3CHO), with C2H3OH/CH3CHO ∼ 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. Key words. astrochemistry – line: identification – ISM: individual objects: TMC-1 – ISM: molecules – radio lines: ISM 1. Introduction (e.g., Agúndez & Wakelam 2013). Here we report the detec- tion of four O-bearing COMs toward TMC-1(CP). Prope- Complex organic molecules (COMs) such as methyl formate nal (C2H3CHO) had previously been reported toward massive (HCOOCH3) and dimethyl ether (CH3OCH3) have traditionally star-forming regions in the Galactic center (Hollis et al. 2004; been observed in the warm gas around protostars, the so-called Requena-Torres et al. 2008) and in the hot corino IRAS 16293- hot cores and corinos, where they are thought to form upon ther- 2422 B (Manigand et al. 2021). Vinyl alcohol (C2H3OH) had mal desorption of ice mantles on grains (Herbst & van Dishoeck only been seen toward Sagittarius B2(N), where the high spectral 2009). In the last decade, these molecules have also been density complicates its identification (Turner & Apponi 2001). observed in a few cold sources, such as the dense cores Therefore, this is the first clear detection of C H OH in space B1-b (Öberg et al. 2010; Cernicharo et al. 2012) and L483 2 3 and the first time that C2H3CHO and C2H3OH have been (Agúndez et al. 2019), the dark cloud Barnard 5 (Taquet et al. detected in a cold environment. We also report the detection of 2017), the pre-stellar cores L1689B (Bacmann et al. 2012) and HCOOCH3 and CH3OCH3, recently detected (the latter tenta- L1544 (Jiménez-Serra et al. 2016), and the starless core TMC- tively) toward the methanol peak of TMC-1 (Soma et al. 2018) 1 (Soma et al. 2018). The low temperatures in these environ- but not toward TMC-1(CP). ments inhibit thermal desorption, and how these molecules are formed, whether in the gas phase or on grain surfaces fol- lowed by some nonthermal desorption process, is still an active 2. Astronomical observations subject of debate (Vasyunin & Herbst 2013; Ruaud et al. 2015; Balucani et al. 2015; Chang & Herbst 2016; Vasyunin et al. The data presented here belong to a Q-band line survey of h m s ◦ 0 00 2017; Shingledecker et al. 2018; Jin & Garrod 2020). TMC-1(CP), αJ2000 = 4 41 41:9 and δJ2000 = +25 41 27:0 , The cyanopolyyne peak of TMC-1, TMC-1(CP), is char- performed with the Yebes 40m telescope. The cryogenic receiver acterized by a carbon-rich chemistry, with high abundances for the Q band, which was built within the Nanocosmos of carbon chains and a low content of O-bearing COMs project1 and covers the 31.0–50.4 GHz frequency range with horizontal and vertical polarizations, was used connected to ? Based on observations carried out with the Yebes 40m telescope Fast Fourier Transform spectrometers, which cover a band- (projects 19A003, 20A014, and 20D023). The 40m radio telescope width of 8 × 2:5 GHz in each polarization with a spectral at Yebes Observatory is operated by the Spanish Geographic Institute (IGN; Ministerio de Transportes, Movilidad y Agenda Urbana). 1 https://nanocosmos.iff.csic.es Article published by EDP Sciences L4, page 1 of6 A&A 649, L4 (2021) Table 1. Observed line parameters of the target O-bearing COMs of this study in TMC-1. ∗ (a) R ∗ (b) (c) Molecule Transition Eup νcalc TA peak ∆v VLSR TAdv S/N Beff/Feff (K) (MHz) (mK) (km s−1) (km s−1) (mK km s−1)(σ) trans-C2H3CHO 41;4 − 31;3 6.2 34 768.987 3:06 ± 0:31 0:62 ± 0:08 5:77 ± 0:03 2:03 ± 0:21 14.5 0.603 40;4 − 30;3 4.3 35 578.136 3:77 ± 0:33 0:81 ± 0:08 5:79 ± 0:03 3:27 ± 0:27 19.4 0.597 41;3 − 31;2 6.4 36 435.990 3:17 ± 0:29 0:85 ± 0:09 5:73 ± 0:04 2:87 ± 0:25 19.2 0.590 51;5 − 41;4 8.3 43 455.469 1:81 ± 0:49 0:72 ± 0:27 5:78 ± 0:08 1:38 ± 0:37 6.5 0.530 50;5 − 40;4 6.4 44 449.749 3:67 ± 0:54 0:54 ± 0:08 5:80 ± 0:04 2:11 ± 0:31 10.5 0.521 51;4 − 41;3 8.6 45 538.994 4:72 ± 0:66 0:69 ± 0:09 5:80 ± 0:04 3:45 ± 0:43 12.6 0.511 syn-C2H3OH 40;4 − 31;3 9.3 32 449.221 1:17 ± 0:32 1:07 ± 0:21 5:61 ± 0:11 1:34 ± 0:27 6.8 0.622 (d) 21;2 − 11;1 5.1 37 459.184 – – – – – 0.581 20;2 − 10;1 2.8 39 016.387 1:90 ± 0:39 0:89 ± 0:16 5:81 ± 0:07 1:79 ± 0:29 9.0 0.568 21;1 − 11;0 5.3 40 650.606 1:71 ± 0:41 0:65 ± 0:19 5:88 ± 0:08 1:18 ± 0:28 6.7 0.554 HCOOCH3 31;3 − 21;2 E 4.0 34 156.889 1:92 ± 0:29 0:62 ± 0:12 5:93 ± 0:06 1:27 ± 0:23 9.6 0.608 31;3 − 21;2 A 3.9 34 158.061 1:86 ± 0:29 0:80 ± 0:16 5:84 ± 0:07 1:59 ± 0:28 10.6 0.608 (e) 30;3 − 20;2 E 3.5 36 102.227 – – – – – 0.593 30;3 − 20;2 A 3.5 36 104.775 2:61 ± 0:29 0:74 ± 0:09 5:80 ± 0:04 2:05 ± 0:22 14.6 0.592 31;2 − 21;1 E 4.4 38 976.085 1:81 ± 0:35 0:66 ± 0:14 5:93 ± 0:07 1:28 ± 0:25 8.3 0.568 31;2 − 21;1 A 4.4 38 980.803 2:45 ± 0:35 0:57 ± 0:09 5:92 ± 0:04 1:49 ± 0:21 10.4 0.568 41;4 − 31;3 E 6.1 45 395.802 2:82 ± 0:57 0:63 ± 0:18 6:00 ± 0:07 1:89 ± 0:40 8.3 0.512 41;4 − 31;3 A 6.1 45 397.360 2:39 ± 0:57 0:42 ± 0:19 5:91 ± 0:10 1:07 ± 0:32 5.8 0.512 40;4 − 30;3 E 5.8 47 534.116 3:19 ± 0:75 0:59 ± 0:12 5:92 ± 0:07 2:01 ± 0:44 7.1 0.493 40;4 − 30;3 A 5.8 47 536.905 2:76 ± 0:75 0:98 ± 0:23 5:99 ± 0:10 2:88 ± 0:60 7.9 0.493 CH3OCH3 21;1 − 20;2 AE+EA 4.2 31 105.223 1:35 ± 0:39 0:92 ± 0:25 5:72 ± 0:13 1:31 ± 0:36 5.8 0.632 21;1 − 20;2 EE 4.2 31 106.150 1:52 ± 0:39 0:54 ± 0:34 5:94 ± 0:08 0:87 ± 0:29 5.0 0.632 31;2 − 30;3 AE+EA 7.0 32 977.276 1:37 ± 0:25 0:63 ± 0:13 5:84 ± 0:07 0:91 ± 0:19 7.8 0.618 31;2 − 30;3 EE 7.0 32 978.232 1:37 ± 0:25 0:95 ± 0:23 5:84 ± 0:09 1:38 ± 0:27 9.6 0.618 31;2 − 30;3 AA 7.0 32 979.187 1:06 ± 0:25 0:85 ± 0:32 5:99 ± 0:12 0:96 ± 0:29 7.1 0.618 41;3 − 40;4 EE 10.8 35 593.408 1:22 ± 0:27 0:56 ± 0:13 5:82 ± 0:07 0:73 ± 0:16 6.4 0.597 11;1 − 00;0 EE 2.3 47 674.967 3:31 ± 0:62 0:59 ± 0:12 6:02 ± 0:06 2:08 ± 0:38 8.9 0.492 R Notes.