ALMA Observations of Molecular Complexity in the Large Magellanic Cloud: The N 105 Star-forming Region

Abstract

The Large Magellanic Cloud (LMC) is the nearest laboratory for detailed studies on the formation and survival of complex organic molecules (COMs), including biologically important ones, in low-metallicity environments—typical of earlier cosmological epochs. We report the results of 1.2 mm continuum and molecular line observations of three fields in the star-forming region N 105 with the Atacama Large Millimeter/submillimeter Array. N 105 lies at the western edge of the LMC bar with ongoing star formation traced by H2O, OH, and CH3OH masers, ultracompact H ii regions, and young stellar objects. Based on the spectral line modeling, we estimated rotational temperatures, column densities, and fractional molecular abundances for 12 1.2 mm continuum sources. We identified sources with a range of chemical makeups, including two bona fide hot cores and four hot core candidates. The CH3OH emission is widespread and associated with all the continuum sources. COMs CH3CN and CH3OCH3 are detected toward two hot cores in N 105 together with smaller molecules typically found in Galactic hot cores (e.g., SO2, SO, and HNCO) with the molecular abundances roughly scaling with metallicity. We report a tentative detection of the astrobiologically relevant formamide molecule (NH2CHO) toward one of the hot cores; if confirmed, this would be the first detection of NH2CHO in an extragalactic subsolar metallicity environment. We suggest that metallicity inhomogeneities resulting from the tidal interactions between the LMC and the Small Magellanic Cloud might have led to the observed large variations in COM abundances in LMC hot cores.

The Detection of Deuterated Water in the Large Magellanic Cloud with ALMA

“…Figure 2 shows selected frequency ranges of the ALMA Band 6 spectra of hot cores N 105-2 A and B, covering the HDO 241.6 GHz line, as well as the methanol (CH 3 OH) J = 5-4 Q-branch at ∼241.8 GHz and the methyl cyanide (CH 3 CN) 14 K -13 K ladder for reference. The molecular line identification and spectral modeling for all spectral windows were performed for all the continuum sources in N 105-2 in Sewiło et al (2022).…”

“…We detected the HDO 2 11 -2 12 line at 241.5616 GHz with ALMA toward hot cores N 105-2 A and N 105-2 B in the starforming region N 105 in the Large Magellanic Cloud (LMC; briefly reported in Sewiło et al 2022). These are two out of only a handful of known bona fide extragalactic hot cores, all located in the LMC (Shimonishi et al 2016b(Shimonishi et al , 2020Sewiło et al 2018Sewiło et al , 2019Sewiło et al , 2022 The LMC, an irregular dwarf galaxy, is the most massive and one of the nearest (50.0 ± 1.1 kpc; Pietrzyński et al 2013) satellites of the Milky Way.…”

“…We detected the HDO 2 11 -2 12 line at 241.5616 GHz with ALMA toward hot cores N 105-2 A and N 105-2 B in the starforming region N 105 in the Large Magellanic Cloud (LMC; briefly reported in Sewiło et al 2022). These are two out of only a handful of known bona fide extragalactic hot cores, all located in the LMC (Shimonishi et al 2016b(Shimonishi et al , 2020Sewiło et al 2018Sewiło et al , 2019Sewiło et al , 2022 The LMC, an irregular dwarf galaxy, is the most massive and one of the nearest (50.0 ± 1.1 kpc; Pietrzyński et al 2013) satellites of the Milky Way. The low metallicity of the LMC (Z ∼ 0.3-0.5 Z e ; Russell & Dopita 1992;Westerlund 1997;Rolleston et al 2002), similar to galaxies at the peak of star formation in the Universe (z ∼ 1.5; e.g., Pei et al 1999;Mehlert et al 2002;Madau & Dickinson 2014), provides a unique opportunity to study star formation (including the H 2 O and HDO chemistry) in an environment that is significantly different than in today's Galaxy.…”

“…In the more recent interferometric studies, deuterated molecules have been detected toward the LMC hot cores and hot core candidates. DCN was detected in two hot cores in N 113 (N 113 A1 and N 113 B3;Sewiło et al 2018), deuterated hydrogen sulfide (HDS) toward a hot core candidate N 105-2 C, HDO toward hot cores N 105-2 A and N 105-2 B, and deuterated formaldehyde (HDCO) toward N 105-2 A (Sewiło et al 2022). In this paper, we provide a detailed discussion on the detection of HDO toward N 105-2 A and 2 B: the first detection of HDO toward an extragalactic hot core.…”

CHEMOUT: CHEMical complexity in star-forming regions of the OUTer Galaxy. II. Methanol formation at low metallicity

“…This indicates that, even at metallicities lower than the Solar one, planets capable to host life can be found, depending also on the dynamical history of the planet host stars (Dai et al 2021), which is likely to be different in the inner and outer Galaxy. Second, observations performed with the Atacama Large Millimeter Array (ALMA) towards the Large and Small Magellanic Clouds (LMC and SMC, Shimonishi et al 2018, Sewiło et al 2018, Sewiło et al 2022, two external galaxies having metallicity ∼ 3 and ∼ 5 times lower than Solar, respectively, have detected emission of complex organic molecules (COMs), which are organic species with more than five atoms. This finding, and the recent discovery of a hot molecular core rich in COMs at GC of ∼ 19 kpc (Shimonishi et al 2021), have clearly suggested that the astrochemical processes that can lead to species of pre-biotic interest can be found also in metal poor environments.…”