ALCHEMI: an ALMA Comprehensive High-resolution Extragalactic Molecular Inventory. Survey presentation and first results from the ACA array

Abstract

We used the Atacama Large Millimeter/submillimeter Array (ALMA), covering a nearly contiguous 289 GHz frequency range between 84.2 and 373.2 GHz, to image the continuum and spectral line emission at 1.6\arcsec ($\sim 28$ pc) resolution down to a sensitivity of $30-50$ mK. This article describes the ALMA Comprehensive High-resolution Extragalactic Molecular Inventory (ALCHEMI) Large Program. We focus on the analysis of the spectra extracted from the $15^{\prime \prime }$ ($\sim 255$ pc) resolution ALMA Compact Array data. We model the molecular emission assuming local thermodynamic equilibrium with 78 species detected. Additionally, multiple hydrogen and helium recombination lines are identified. Spectral lines contribute 5 to 36\% of the total emission in frequency bins of 50 GHz. We report the first extragalactic detections of C${}_2$H${}_5$OH, HOCN, HC${}_3$HO, and several rare isotopologues. Isotopic ratios of carbon, oxygen, sulfur, nitrogen and silicon were measure with multiple species. Infrared pumped vibrationaly excited HCN, HNC, and HC${}_3$N emission, originating in massive star formation locations, is clearly detected at low resolution, while we do not detect it for HCO${}^{+}$. We suggest high temperature conditions in these regions driving a seemingly "carbon-rich" chemistry which may also explain the observed high abundance of organic species close to those in Galactic hot cores. The $L_{vib}/L_{IR}$ ratio is used as a proxy to estimate a $3\%$ contribution from proto super star cluster to the global infrared emission. Measured isotopic ratios with high dipole moment species agree with those within the central kiloparsec of the Galaxy, while those derived from ${}^{13}{\mathrm{C}}^{18}\mathrm{O}$ are a factor of 5 larger, confirming the existence of multiple ISM components within NGC 253 with different degrees of nucleosynthesis enrichment. ALCHEMI provides a template for early Universe galaxies.

60 pages, 32 figures, 15 tables, Accepted for publication at A&A

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Cited by in corpus (42)

• Precursors of fatty alcohols in the ISM: Discovery of n-propanol
• Carbon-Chain Chemistry in the Interstellar Medium
• Tracing Interstellar Heating: An ALCHEMI Measurement of the HCN Isomers in NGC 253
• PHANGS-JWST First Results: Rapid Evolution of Star Formation in the Central Molecular Gas Ring of NGC1365
• The Distribution and Origin of C${}_2$H in NGC 253 from ALCHEMI
• First extragalactic detection of a phosphorus-bearing molecule with ALCHEMI: phosphorus nitride (PN)
• Starburst Energy Feedback Seen Through HCO${}^{+}$/HOC${}^{+}$ Emission in NGC 253 from ALCHEMI
• Energizing Star Formation: The Cosmic Ray Ionization Rate in NGC 253 Derived From ALCHEMI Measurements of H${}_3$O${}^{+}$ and SO
• The Morpho-Kinematic Architecture of Super Star Clusters in the Center of NGC253
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• Reconstructing the shock history in the CMZ of NGC 253 with ALCHEMI
• SUNRISE: The rich molecular inventory of high-redshift dusty galaxies revealed by broadband spectral line surveys
• Surveying the Whirlpool at Arcseconds with NOEMA (SWAN)- I. Mapping the HCN and N${}_2$H${}^{+}$ 3mm lines
• Infrared view of the multiphase ISM in NGC 253 I. Observations and fundamental parameters of the ionised gas
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• A nearly constant CN/HCN line ratio in nearby galaxies: CN as a new tracer of dense gas
• Sulfur isotope ratios in the Large Magellanic Cloud
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• An accurate set of H${}_3$O${}^{+}-$ H${}_2$ collisional rate coefficients for non-LTE modelling of warm interstellar clouds
• Molecular isotopologue measurements toward super star clusters and the relation to their ages in NGC253 with ALCHEMI
• ALMA Sub-arcsec-resolution 183 GHz H2O and Dense Molecular Line Observations of Nearby Ultraluminous Infrared Galaxies
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• A 260 pc resolution ALMA map of HCN(1-0) in the galaxy NGC 4321
• Complex Organic Molecules towards the central molecular zone of NGC 253
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