Estudio submilimétrico de galaxias cercanas
The formation of molecules in the Interstellar medium is possible under the condition of high densities in a given region as the consequence of the occurrence of collisions between atoms. Moreover, a molecule can be dissociated by an UV photon. Interestelar dust can act as a pro- tection against dissociation since it will absorb any UV radiation. Hence the combination of a high particle density and the presence dust grains help the production and maintenence of molecules that are in the dense and cold regions of the Interstellar medium.
The formation of hydrogen molecules takes place in reactions on the surface of dust grains which act as catalysts of the reaction and absorb the excess of free energy during the formation of the H2 molecule.
The basic mechanism of molecular formation in the Interstellar medium is the occurrence of reactions in which one of the particles involved is charged; these are named ion-molecule reactions. This kind of reactions can be produced because in the molecular clouds there are ions, due to cosmic rays inside the molecular cloud.
The photodisociation of the molecular gas by UV fields (PDRs regions) is produced by the emi- sion of OB star groups formed in the starburst. The molecular emission from the central regions of active galaxies is a powerfull tool to understand the physical processes that give rise to the nuclear activity. The study of key molecular tracers and their abundance ratios can be used to establish if the dominant heating mechanism is due to shocks, photodisociation regions (PDR) or X-ray dominated regions (XDRs). Shocks, UV radiation, X rays and cosmic rays play an important rol in the chemistry of molecular clouds in the nuclei of galaxies.
These collisions generate icy mantles of carbon monoxide, water and methanol around dust grains in high extinction regions with densities of higher than 104 cm-3. The mantle material could be returned to the gas phase by evaporation or shock waves. Strong shocks can break the grains, and it is thought that the presence of SiO in the gas phase is an indicator of the presence of such shocks. […]
