NGC 3603 PDR region

Ultraviolet photons from O and B stars strongly influence the structure and emission spectra of the interstellar medium. The UV photons energetic enough to ionize hydrogen \(h\nu > {\rm 13.6 eV}\) will create the H II region around the star, but lower energy UV photons escape. These far-UV photons (\(6~{\rm eV} < h\nu < {\rm 13.6~eV}\)) are still energetic enough to photodissociate molecules and to ionize low ionization-potential atoms such as carbon, silicon, and sulfur. They thus create a photodissociation region (PDR) just outside the H II region. In aggregate, these PDRs dominates the heating and cooling of the neutral interstellar medium. The gas is heated by photo-electrons from grains and cools mostly through far-infrared fine structure lines like [O I] and [C II].

The PDR Toolbox is an open-source, science-enabling tool for the community, designed to help astronomers determine the physical parameters of photodissociation regions from observations. Typical observations of both Galactic and extragalactic PDRs come from ground- and space-based millimeter, submillimeter, and far-infrared telescopes such as ALMA, SOFIA, JWST, Spitzer, and Herschel. Given a set of observations of spectral line or continuum intensities, PDR Toolbox can compute best-fit FUV incident intensity and cloud density based on our models of PDR emission. One can also fit H2 rovibrational emission excitation diagrams to determine temperature, column density, and ortho-to-para ratio.

The current version is 2.2.6 (released April 12, 2022)

Recent Release Highlights

  • Updated and expanded Wolfire-Kaufman models

    The 2020 WK model set includes updated physics and more CO, H2, and Fe II lines. Newly included are 13CO models.

  • KOSMA-tau PDR models

    We now include KOSMA-tau PDR models for both clumpy and non-clumpy media. This will provide users the ability to easily compare their observations to models from different PDR codes using the dandy tools in the PDR Toolbox.

  • H2 excitation diagram fitting

    The H2 excitation fitting tool will create of maps of temperature, column density, and ortho-to-para ratio from observations.

  • Improved fitting of observations to models

    All fitting now uses the LMFIT package, allowing users to choose the fitting method (e.g., least-squares, MCMC) and giving them more details on quality of fit.

Please remember to cite use of the PDR Toolbox!
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Citing PDR Toolbox

If you use the PDR Toolbox for published research or in a presentation, we ask that you please cite the following references:


Twenty years ago, when we started the Photodissociation Region Toolbox (PDRT), web programming meant Common Gateway Interface and Perl was King. Single pixel detectors were cutting edge technology and the sub-mm window had just begun to be explored. Airline travel was pleasant and people still smoked cigarettes. We put together PDRT with Perl, HTML, Apache 1.3, FITS files, CVS, shell scripts, thumb tacks, horsehair, and bits of string. The tool filled a need, scratched an itch, developed an international user base. As new telescopes arrived, we added spectral lines and low metallicity models. Web-free scripting interfaces were created by users. Our funding ran out, but we added lines when users requested and kept the service running. Single pixel detectors gave way to pixel arrays and the sub-mm science matured. Recently, we received funding to implement upgrades described here. Let us know which are most important to you and what else you'd like to see!


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