Chemical signatures of a prestellar cluster in the Galactic Center

The Central Molecular Zone (CMZ) contains most of the mass of our Galaxy, but its star formation rate is one order of magnitude lower than in the Galactic disk. This is likely related to the fact that the bulk of the gas in the CMZ is in a warm (100 K) and turbulent phase with little material in the prestellar phase. I will present D/H ratios of HCN, HNC, HCO+, and N2H+ obtained towards the CMZ molecular cloud G+0.693-0.027 (Colzi et al. 2022). These observations clearly show, for the first time, the presence of a colder, denser and narrow component, with a line width of about 9 km s-1, in addition to the warm, less dense, and turbulent broad component with a line width of about 20 km s-1. For this new component D/H ratios higher than 1e-4 and excitation temperatures of 7 K for all molecules have been found, suggesting kinetic temperatures lower than 30 K and H2 densities higher than 5e4 cm-3. This new method indicates that the degree of deuteration of different molecules, such as N2H+ and HCO+, and their line profiles, can be used to reveal the different gas components in the line of sight to the CMZ. Then, I will present HC3N excitation-derived gas densities and temperatures of the gas components towards the same source, using multiple transitions coupled with spatially resolved HC3N images of the source. This approach allows us to identify denser gas that possibly is on the verge of gravitational collapse and that will host future protostars in the CMZ (Colzi et al. 2024).