PDRs and XDRs

Astronomy Department, University of Maryland, College Park, MD 20742, USA ;
e-mail: mwolfire@astro.umd.edu

Abstract

Photodissociation regions (PDRs) are gas phases in which far-ultraviolet radiation plays a significant role in the heating and/or chemistry (Tielens & Hollenbach 1985). X-ray dissociation regions (XDRs) are regions in which X-rays dominate the heating and/or chemistry (Moloney et al. 1996). Much progress has been mode in modeling PDRs (e.g., Röllig et al. 2007) and XDRs (e.g., Meijerink et al. 2007) and the models predict several line intensities and line ratios of atomic and molecular species that are good diagnostics for discriminating between the two. I will discuss the theoretical models in light of the most recent observations.