Metallicity in Photon Dominated Regions

Dense molecular ISM is the site of star formation. FUV radiation from hot stars heat the nearby molecular gas establishing a region called Photon Dominated Regions (PDRs), where the physical and the chemical processes are dominated by the FUV field. The UV radiation not only heats the molecular gas but also regulates the star formation process itself. In low metallicity systems, such as LMC, SMC and dwarf galaxies, a reduced number of dust grains and heavy elements per hydrogen atom, plays a significant role on the chemistry and heating of the gas in PDRs. The UV radiation penetrates much deeper into the medium dissociating CO and producing a large layer of CI and CII. Observations show that the ratio of [CII]-158 micron line emission to the CO rotational line emission is much higher for dwarf galaxies than the Galaxy.
We study the effects of reduced metallicity on the temperature and chemical structure of PDRs. We use this model to study the dependence of the important cooling lines of CII, CI and CO on metallicity. We also compare our results with the results obtained using a semi-analytical approach by Bolatto et al., (1999).