Astronomy:Photodissociation region
In astrophysics, photodissociation regions (or photon-dominated regions, PDRs) are predominantly neutral regions of the interstellar medium in which far ultraviolet photons strongly influence the gas chemistry and act as the most important source of heat.[1] They occur in any region of interstellar gas that is dense and cold enough to remain neutral, but that has too low a column density to prevent the penetration of far-UV photons from distant, massive stars. A typical and well-studied example is the gas at the boundary of a giant molecular cloud.[1] PDRs are also associated with HII regions, reflection nebulae, active galactic nuclei, and Planetary nebulae.[2] All the atomic gas and most of the molecular gas in the galaxy is found in PDRs.[3]
History
The study of photodissociation regions began from early observations of the star-forming regions Orion A and M17 which showed neutral areas bright in infrared radiation lying outside ionised HII regions.[3]
References
- ↑ 1.0 1.1 Hollenbach, D.J.; Tielens, A.G.G.M. (1999). "Photodissociation regions in the interstellar medium of galaxies". Reviews of Modern Physics 71 (1): 173–230. doi:10.1103/RevModPhys.71.173. Bibcode: 1999RvMP...71..173H. https://zenodo.org/record/1233981.
- ↑ Tielens, A.G.G.M. (1993). "Photodissociation regions and planetary nebulae". Planetary Nebulae: Proceedings of the 155 Symposium of the International Astronomical Union 155: 155–162. doi:10.1017/S0074180900170330. Bibcode: 1993IAUS..155..155T.
- ↑ 3.0 3.1 Hollenbach, D. J.; Tielens, A. G. G. M. (1997). "Dense photodissociation regions". Annual Review of Astronomy and Astrophysics 35: 179–215. doi:10.1146/annurev.astro.35.1.179. Bibcode: 1997ARA&A..35..179H. https://zenodo.org/record/1234927.
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