Prevalence of Complex Organic Molecules in Starless and Prestellar Cores within the Taurus Molecular Cloud

Maps (greyscale is H2 column density) of the (left) B211 and (right) B10 regions illustrating the complex velocity structure of methanol emission. On the left map three panels of spectra are shown, with C18O (1-0) molecular observations from the IRAM 30m telescope in black (Hacar et al. 2013). For comparison, we include the positions of the methanol peaks which shows similar velocity structure as C18O (1-0). We shifted the bright A+ to the center to show how the vLSR’s compare, showing some misalignment perhaps due to gas motions within the filament. The yellow circles represent cores targeted in those regions. In B211 we also note with a yellow arrow where cores Seo18 and Seo19 lie from Seo et al. 2015 (these weren’t targeted for APS measurements due to overlapping beams). For both regions main beam temperature contours (in steps of 0.2 K starting at 0.2 K) were created in cyan at the velocity of ∼7 km s−1 , in lime at the velocity of ∼6 km s−1 and in magenta the velocity of ∼5 km s−1

The detection of complex organic molecules (COMs) toward dense, collapsing prestellar cores has sparked interest in the fields of astrochemistry and astrobiology, yet the mechanisms for COM formation are still debated.

It was originally believed that COMs initially form in ices which are then irradiated by UV radiation from the surrounding interstellar radiation field as well as forming protostars and subsequently photodesorbed into the gas-phase. However, starless and prestellar cores do not have internal protostars to heat-up and sublimate the ices. Alternative models using chemical energy have been developed to explain the desorption of COMs, yet in order to test these models robust measurements of COM abundances are needed toward representative samples of cores.

We've conducted a large-sample survey of 31 starless and prestellar cores in the Taurus Molecular Cloud, detecting methanol (CH3OH) in 100% of the cores targeted and acetaldehyde (CH3CHO) in 70%. At least two transition lines of each molecule were measured, allowing us to place tight constraints on excitation temperature, column density and abundance. Additional mapping of methanol revealed extended emission, detected down to AV as low as ∼ 3 mag.

We find complex organic molecules are detectable in the gas-phase and are being formed early, at least hundreds of thousands of years prior to star and planet formation. The precursor molecule, CH3OH, may be chemically linked to the more complex CH3CHO, however higher spatial resolution maps are needed to further test chemical models.

Samantha Scibelli, Yancy Shirley
(Submitted on 6 Feb 2020)
Comments: Accepted to ApJ. 23 pages, 14 Figures, 9 Tables
Subjects: Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2002.02469 [astro-ph.GA] (or arXiv:2002.02469v1 [astro-ph.GA] for this version)
Submission history
From: Samantha Scibelli
[v1] Thu, 6 Feb 2020 19:00:18 UTC (1,951 KB)
Astrobiology, Astrochemistry

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