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

TL;DR

This study applies a one-dimensional PDR model to the Taurus molecular cloud to estimate hydrogen densities, compare with CO and infrared data, and evaluate the model's accuracy and assumptions in a well-studied galactic region.

Contribution

It demonstrates the application of a PDR model to a galactic cloud, providing detailed comparisons with CO and dust emission data, and discusses the model's implications and limitations.

Findings

Derived hydrogen densities of ~430 cm-3 consistent with literature.

Found a CO conversion factor at the low end of reported values.

Noted potential underestimation of total hydrogen gas due to assumptions about G0.

Abstract

In this contribution, we test our previously published one-dimensional PDR model for deriving total hydrogen volume densities from HI 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 UV flux G0 of 4.25 ({\chi} = 5) throughout the main body of the cloud, we derive total hydrogen volume densities of \approx 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 parsec 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 x 1020 cm-2 (K km s-1)-1), although this value is directly proportional to our assumed value of G0 as well as the cloud depth. We seem to under-predict the total hydrogen gas as compared to 100 {\mu}m dust emission, which we speculate may be caused by a higher actual G0 incident on the Taurus cloud than is generally assumed.