ALCHEMI: First Results from the ALMA Comprehensive High-resolution Extragalactic Molecular Inventory of NGC253

Jeff Mangum
2020 Zenodo  
The dramatic increase in sensitivity and frequency coverage of radio, millimeter, and submillimeter facilities in the last decade has made it possible for the first time to study the chemical complexity of the molecular interstellar medium (ISM) in galaxies beyond the Milky Way. Both spatially resolved observations in nearby galaxies (e.g., Meier & Turner, 2005; Meier+2015; Martin+2015, Izumi+2015) and unresolved surveys (e.g., Krips+2008; Costagliola+2011) have gathered substantial evidence of
more » ... tantial evidence of a great variety in molecular gas composition and excitation across galaxies. Spectral line surveys (e.g., Martin+2011, Aladro+2015, Costagliola+2015) reveal significant differences in the chemical properties of the ISM in starburst galaxies, and suggest that chemistry may be an important diagnostic of evolutionary stage. ISM chemical cycling and enrichment by star formation can be assessed through observations of molecular isotopologues and the derivation of isotopic ratios (e.g., the 12C/13C and 16O/18O ratios: Rangwala+2011, Henkel+2014, Falstad+2015). ISM energy exchange and mechanical feedback from the starburst process can be studied through other molecular species that trace shocked gas and dust (e.g., SiO, HNCO, CH3OH: e.g., Garcia-Burillo+2001, Usero+2006, Meier & Turner 2012). Ultimately, molecular tracers of ISM chemistry probe the fundamental regulation of the star formation process in galaxies. To this end, we are conducting a multi-band spectral line survey within the nearby starburst galaxy NGC253. The ALMA Comprehensive High-resolution Extragalactic Molecular Inventory (ALCHEMI), an ALMA Cycle 5 Large Programme, encompasses the entirety of ALMA Bands 3, 4, 6, and 7 (85 to 366 GHz). A complimentary ALMA Cycle 6 program adds imaging of the ALCHEMI field at ALMA Band 5. ALCHEMI images the central several hundred parsec area of NGC253 using both the 12m Array and the Atacama Compact Array (ACA) to cover most of the central molecular zone (50x20 arcsec field) at 1.5 arcsec (25 pc) spatial and 10 km/s spec [...]
doi:10.5281/zenodo.3629756 fatcat:rrwbtzpcvjbx7ff5bca5dpafh4