HCl in massive star-forming regions across various scales

Although its nucleosynthesis history is not fully understood, Cl is primarily produced in the interstellar medium via core-collapse supernovae, with the weak s-process in massive stars as a secondary source of ³⁷Cl. Stellar models predict a ³⁵Cl/³⁷Cl ratio between 1 and 5, but observations of Cl-bearing molecules have been limited due to their high-lying transitions. I will present recent observations of the HCl 1–0 line at 625 GHz, carried out using the SEPIA660 receiver on the APEX 12 m sub-mm telescope. We detected both isotopologues toward 27 Galactic sources, spanning a range of Galactocentric radii, doubling the number of sources where it has previously been detected. Of these, 11 show pure emission with possible outflow features, while the remaining display complex profiles with mixed emission and absorption. An average isotopic ratio of 2.4±0.8 was found, with no clear trend with galactocentric radius. The observed outflow wings motivated us to map HCl emission in the massive star-forming region IRAS 12326-6245, probing chlorine distribution and isotopic ratio on smaller scales. Following its ubiquitous abundance across the Milky Way, HCl was also investigated towards nearby galaxies; it was detected in absorption toward NGC 4945, which marks the first detection of HCl in a nearby galaxy.