Science Highlight

ISM properties of the central molecular zone of the nearby starburst galaxy NGC 253 was investigated using the ultra-wide millimeter spectral scan survey. With this dataset, Harada et al. presented an atlas of velocity-integrated images at a 1".6 resolution of 148 transitions from 44 species (Astrophys. J. Suppl. 271, 38 (2024)). This includes the first detection of HCNH+ and the first interferometric images of C3H+, NO, HCS+ in an external galaxy. A principal component analysis shows correlations between molecular line intensities at different sky positions: Young starbursts tend to have peaks of high-excitation transitions of HC3N and complex organic molecules, while more developed starbursts have peaks of radio recombination lines and high-excitation transitions of radicals, like CN, CCH. Low-excitation shock tracers (CH3OH, HNCO, HOCO+, and OCS) do not correlate with star formation, and likely trace shocks caused by cloud collisions. On the other hand, High-excitation transitions of SiO may originate from star formation. This type of analysis provides valuable insight into interstellar processes even in other galaxies, and the findings will be a particularly useful reference for observational studies.  This exploration was conducted as part of the ALMA Large Program, ALMA Comprehensive High-resolution Extragalactic Molecular Inventory, ALCHEMI, by S. Martin, N. Harada, J. and J. Mangum.