Establishing a timeline for the high-mass star formation process

This thesis aims to answer a long-standing astrophysical problem, quantifying the timescales of the evolutionary phases characterising the high-mass star formation process. Understanding the details of the formation of massive stars (i.e. M>8-10 Msun) is not trivial, since these objects are rare and at a relatively large distance. They also form and evolve very quickly and almost their entire formation takes place deeply embedded in their parental clumps. During the evolution, the chemical composition of the massive clump can be heavily affected by the changes in density and temperature induced by the presence of massive young stellar objects. Chemical tracers that show a relation between their observed abundances and the different phases of the star formation process are commonly called chemical clocks. In this Thesis, through the comparison of observations of a large sample of massive clumps in different evolutionary stages, and accurate time-dependent chemical models, we estimate the timescales of the different phases over the entire star formation process. In addition, we provide relevant information on the reliability of crucial chemical clocks, both for the early and the late stages, confirming that chemistry is a powerful tool to establish a timeline for the high-mass star formation process.