ALMAGAL First Results: Robust temperatures and luminosities of cores in a thousand high-mass cluster-forming regions

The ALMA Large Program ALMAGAL has observed over 1000 high-mass star forming clumps and unveiled the many ~1000 au protostellar cores embedded within. For the first time, interferometric spectral line data is now available toward a significant fraction of the total Galactic population of high-mass star formation sites and we present the first catalogue of temperatures and luminosities for all detected cores. With a coherent data set and homogeneous analysis, we then draw statistically significant global conclusions about their physical properties. With such a rich sample, we also explore - and quantify - the scope and limitations of several molecular temperature tracers. Degeneracies in the underlying parameter spaces that reproduce spectra are explored through massive MCMC realisations; and the effect of assumptions commonly made in spectral analysis is investigated through machine learning techniques trained with spectra of structured sources. With key parameters such as luminosity critically dependent on the temperature, we find that using only best fit temperatures may cause highly misleading conclusions. Determining the credibility range of parameters is vital to draw robust conclusions and truly understand the physical conditions leading to the formation of high-mass stars in our Galaxy.