Applying a one-dimensional PDR model to the Taurus molecular cloud and its atomic envelope

• Published in: Monthly notices of the Royal Astronomical Society 2013-03, Vol.429 (4), p.3584-3595
• Main Authors: Heiner, J. S., Vázquez-Semadeni, E.
• Format: Article
• Language: English
• Subjects: Astrology; Hydrogen; Molecules; Stars & galaxies
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/sts645

In this contribution, we test our previously published one-dimensional PDR model for deriving total hydrogen volume densities from H i column density measurements in extragalactic regions by applying it to the Taurus molecular cloud, where its predictions can be compared to available data. Also, we make the first direct detailed comparison of our model to CO(1-0) and far-infrared emission. Using an incident ultraviolet flux G 0 of 4.25 (χ = 5) throughout the main body of the cloud, we derive total hydrogen volume densities of 430 cm−3, consistent with the extensive literature available on Taurus. The distribution of the volume densities shows a log-normal shape with a hint of a power-law shape on the high density end. We convert our volume densities to H2 column densities assuming a cloud depth of 5 pc and compare these column densities to observed CO emission. We find a slope equivalent to a CO conversion factor relation that is on the low end of reported values for this factor in the literature [0.9 × 1020 cm−2 (K km s−1)−1], although this value is directly proportional to our assumed value of G 0 as well as the cloud depth. We seem to underpredict the total hydrogen gas as compared to 100 μm dust emission, which as we speculate may be caused by a higher actual G 0 incident on the Taurus cloud than is generally assumed.