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 2.4.4 (released Feb 07, 2025)


Release Highlights

  • [O I] 1.316 μm Diagnostic Diagram

    We provide guidance to help to take into account viewing inclination angle when interpreting measured [O I] 1.316 μm emission line (e.g., with JWST).

  • LMC metallicity surface temperature

    We have computed models for surface temperature at the metallicity of the Large Magellenic Cloud (z=0.5).

  • Bug fixes

    We have made several bug fixes and addressed requests for enhancment. Thanks to users who reported issues!

  • Support dropped for Python 3.9
    Since we rely on packages like astropy that require recent versions of Python to use their latest features, we now only support Python 3.10+.
  • ..and more
    The full list of changes can be viewed on our github.

Reference Paper on PDRT

The PhotoDissociation Region Toolbox: Software and Models for Astrophysical Analysis,
Marc W. Pound & Mark G. Wolfire 2023, AJ, 165:25
Read it here.
Please remember to cite use of the PDR Toolbox!
And please join our discussion forum.

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Tools & more

ABOUT

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:

Support

We gratefully acknowledge support from the NASA Astrophysics Data Analysis Program under award numbers 80NSSC24K0634 and 80NSSC19K0573; from JWST-ERS program ID 1288 provided through grants from the STScI under NASA contract NAS5-03127; and from the SOFIA C+ Legacy Project through a grant from NASA through award #208378 issued by USRA.

History

Back in 2001, 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!

CONTACT US

Got a question? Want to tell us about your use of PDRT? Join our googlegroup and drop us a line!