Metallicity effects in Photon Dominated Regions: Clumpy clouds

Several galaxies, such as dwarfs and Irregulars as well as outer galactic clouds have low metallicity. At low metallicities a reduction in the amount of dust and heavy elements plays a significant role on the chemistry as well as the heating and cooling of the gas in the molecular regions, called as Photon Dominated Regions (PDRs). We present here the effects of reduced metallicity in PDRs and study the important PDR cooling lines ([CII], [CI] and CO). Moreover many observational evidences suggest that molecular clouds are clumpy. We model the molecular emission from galaxies incorporating a mass spectrum of clumps. We also compare our results with the semi-analytical results obtained by Bolatto et al. (1999).