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

Abstract

The outer Galaxy is an environment with metallicity lower than the Solar one and, because of this, the formation and survival of molecules in star-forming regions located in the inner and outer Galaxy is expected to be different. To gain understanding on how chemistry changes throughout the Milky Way, it is crucial to observe outer Galaxy star-forming regions to constrain models adapted for lower metallicity environments. The project "chemical complexity in star-forming regions of the outer Galaxy" (CHEMOUT) aims to address this problem observing a sample of 35 high-mass star-forming cores at Galactocentric distances up to ~23 kpc with the IRAM 30m telescope in various 3mm and 2mm bands. In this work we analyse observations of methanol (CH3OH), one of the simplest complex organic molecules crucial for organic chemistry in star-forming regions, and of two chemically related species, HCO and formaldehyde (H2CO), towards 15 out of the 35 targets of the CHEMOUT sample. In fact, only targets previously detected in both HCO and H2CO, both precursors of methanol, were considered. We detected CH3OH in all 15 targets. Using a Local Thermodynamic Equilibrium approach, we derive CH3OH excitation temperatures in the range 7 - 16 K and line widths smaller than 4 km/s, consistent with emission from a cold and quiescent envelope. The CH3OH fractional abundances w.r.t. H2 range between ~0.6 x 10^{-9} and ~7.4 x 10^{-9}. These values are comparable to those found in star-forming regions in the inner and local Galaxy. Our results have important implications in the organic, and possibly pre-biotic, chemistry occurring in the outermost star-forming regions of the Galaxy, and can help setting the frontiers of the Galactic habitable zone.

13 pages, 5 figures, 2 appendices, accepted for publication in A&A

References in corpus (27)

• The Critical Density and the Effective Excitation Density of Commonly Observed Molecular Dense Gas Tracers
• Formation of Complex Molecules in Prestellar Cores: a Multilayer Approach
• Spectral Line Identification and Modelling (SLIM) in the MAdrid Data CUBe Analysis (MADCUBA) package: An interactive software for data cube analysis
• Radial distribution of dust, stars, gas, and star-formation rate in DustPedia face-on galaxies
• The formation of ethylene glycol and other complex organic molecules in star-forming regions
• The Hi-GAL compact source catalogue -- II. The 360° catalogue of clump physical properties
• Simultaneous Hydrogenation and UV-photolysis Experiments of NO in CO-rich Interstellar Ice Analogues; linking HNCO, OCN-, NH2CHO and NH2OH
• The Galactic radial abundance gradients of C, N, O, Ne, S, Cl and Ar from deep spectra of H II regions
• On the "Galactic Habitable Zone"
• Galactocentric variation of the gas-to-dust ratio and its relation with metallicity
• ALCHEMI: an ALMA Comprehensive High-resolution Extragalactic Molecular Inventory. Survey presentation and first results from the ACA array
• The ISM scaling relations in DustPedia late-type galaxies: A benchmark study for the Local Universe
• The radial abundance gradient of oxygen towards the Galactic anticentre
• Metallicity Structure in the Milky Way Disk Revealed by Galactic HII Regions
• Mapping the Galactic Metallicity Gradient with Open Clusters: The State-of-the-Art and Future Challenges
• The Detection of Hot Cores and Complex Organic Molecules in the Large Magellanic Cloud
• Gradients of chemical abundances in the Milky Way from HII regions: distances derived from Gaia EDR3 parallaxes and temperature inhomogeneities
• The detection of a hot molecular core in the extreme outer Galaxy
• The galactic habitable zone of the Milky Way and M31 from chemical evolution models with gas radial flows
• On the variation of carbon abundance in galaxies and its implications
• The Galactic habitable zone around M and FGK stars with chemical evolution models with dust
• Chemistry and physics of a low-metallicity hot core in the Large Magellanic Cloud
• ALMA Observations of Molecular Complexity in the Large Magellanic Cloud: The N105 Star-Forming Region
• Planet Occurrence Rate Correlated to Stellar Dynamical History: Evidence from Kepler and Gaia
• CHEMOUT: CHEMical complexity in star-forming regions of the OUTer Galaxy. I. Organic molecules and tracers of star-formation activity
• A chemical study of carbon fractionation in external galaxies
• Spatial distribution of exoplanet candidates based on Kepler and $Gaia$ data

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