Chemistry here and there: Comparison between the CMZ of the Milky Way and NGC 253

Abstract

For decades, chemical studies in external galaxies have been limited by sensitivity, resolution, bandwidth or a combination of them. A decade of ALMA operations, made the detailed study of the molecular abundances in nearby galaxies a routine job. We can finally bridge the ISM chemistry from Galactic to extragalactic environments, through one to one comparison, albeit probing significantly different scales. The ALMA large program ALCHEMI imaged the chemistry of the starburst galaxy NGC 253 at an unprecedented combination of sensitivity and resolution, achieving a detailed spatially resolved chemical inventory. ALCHEMI probed molecular differences among regions within its CMZ, and allowed the comparison with Galactic environments ranging from hot cores, quiescent molecular clouds and comets. This comparison can be put in the context of available data towards other extragalactic environments. Globally, the comparisons presented here show an astoundingly good correlation between the chemistry in Galactic GMCs and the central molecular zone of NGC 253, ranging scales from 1 pc up to ~0.5 kpc. The wideband sensitivity upgrade of ALMA will expand similar comparisons towards a wider range of Galactic and extragalactic objects.