N159W was the only region where CH 3OH was detected: J = 2–1 and two 3–2 lines at ∼96.7 and ∼145.1 GHz, respectively (see Table 1). The first detection of a COM in the Magellanic Clouds was reported in ref (16) for a SEST 0.85, 1.3, 2, and 3 mm survey of the SMC LIRS 49 (or N27) and LMC 30 Dor-10, 30 Dor-27, N159W, N159S, and N160 regions, covering a range of metallicities and UV radiation strengths. COMs had previously been detected outside the Milky Way, but in galaxies with metallicities comparable to or higher than solar values (see ref (20) and references therein). These observations showed that interstellar COMs can form in the low-metallicity environments, probably in the hot molecular cores and corinos associated with massive and low- to intermediate-mass protostars, respectively. Only very recently have gaseous COMs (methanol: CH 3OH, methyl formate: HCOOCH 3, dimethyl ether: CH 3OCH 3) been detected in the LMC (16−18) and in the SMC, (19) using the Atacama Large Millimeter/sub-millimeter Array (ALMA). The range of metallicities observed in the Magellanic Clouds is similar to that in galaxies at redshift z ≈ 1.5–2, i.e., at the peak of the star formation in the universe (between ∼2.8 and ∼3.5 billion years after the Big Bang e.g., ref (15)), making them ideal templates for studying star formation and complex chemistry in low-metallicity systems in an earlier universe where direct measurements of resolved stellar populations are not possible. All these low-metallicity effects may have direct consequences on the formation efficiency and survival of COMs, although their relative importance remains unclear. Gamma-ray observations indicate that the cosmic-ray density in the LMC and SMC is respectively ∼25% and ∼15% of that measured in the solar neighborhood (refs (13and14)). The interstellar ultraviolet radiation field in the LMC and SMC is 10–100 higher than typical Galactic values (e.g., ref (12)). (5,6) Apart from the lower elemental abundances of gaseous C, O, and N atoms (e.g., ref (7)), low metallicity leads to less shielding (due to the lower dust abundance e.g., refs (8and9)), greater penetration of UV photons into the interstellar medium, and consequently warmer dust grains (e.g., refs (10and11)). They are the nearest star-forming galaxies with metallicities Z (the mass fractions of all the chemical elements other than hydrogen and helium) lower than that in the solar neighborhood ( Z ⊙ = 0.0134): (4) Z LMC ≈ 0.3–0.5 Z ⊙ and Z SMC ≈ 0.2 Z ⊙. The LMC and SMC are gas-rich dwarf companions of the Milky Way located at a distance of (50.0 ± 1.1) kpc (ref (2)) and (62.1 ± 2.0) kpc (ref (3)), respectively. The metallicity of the Magellanic Clouds is similar to that of galaxies in the earlier epochs of the universe thus, the presence of COMs in the LMC and SMC indicates that a similar prebiotic chemistry leading to the emergence of life, as it happened on Earth, is possible in low-metallicity systems in the earlier universe. The detection of COMs in the Magellanic Clouds has important implications for astrobiology. We discuss future prospects for research in the field of complex chemistry in the low-metallicity environment. Theoretical models accounting for the physical conditions and metallicity of hot molecular cores in the Magellanic Clouds have been able to broadly account for the existing observations, but they fail to reproduce the dimethyl ether abundance by more than an order of magnitude. We describe a small and diverse sample of the LMC and SMC sources associated with COMs or hot-core chemistry, and compare the observations to theoretical model predictions. To date, only methanol, methyl formate, and dimethyl ether have been detected in these galaxies-all three toward two hot cores in the N113 star-forming region in the LMC, the only extragalactic sources exhibiting complex hot-core chemistry. The Large and Small Magellanic Clouds (LMC and SMC), gas-rich dwarf companions of the Milky Way, are the nearest laboratories for detailed studies on the formation and survival of complex organic molecules (COMs) under metal-poor conditions.
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