The 2017 Release of Cloudy

Abstract: We describe the 2017 release of the spectral synthesis code Cloudy. A major development since the previous release has been exporting the atomic data into external data files. This greatly simplifies updates and maintenance of the data. Many large datasets have been incorporated with the result that we can now predict well over an order of magnitude more emission lines when all databases are fully used. The use of such large datasets is not realistic for most calculations due to the time and memory needs, and we describe the limited subset of data we use by default. Despite the fact that we now predict significantly more lines than the previous Cloudy release, this version is faster because of optimization of memory access patterns and other tuning. The size and use of the databases can easily be adjusted in the command-line interface. We give examples of the accuracy limits using small models, and the performance requirements of large complete models. We summarize several advances in the H- and He-like iso-electronic sequences. We use our complete collisional-radiative models of the ionization of these one and two-electron ions to establish the highest density for which the coronal or interstellar medium (ISM) approximation works, and the lowest density where Saha or local thermodynamic equilibrium can be assumed. The coronal approximation fails at surprisingly low densities for collisional ionization equilibrium but is valid to higher densities for photoionized gas clouds. Many other improvements to the physics have been made and are described. These include the treatment of isotropic continuum sources such as the cosmic microwave background (CMB) in the reported output, and the ability to follow the evolution of cooling non-equilibrium clouds.

• The paper presents a major update to Cloudy, detailing enhanced data management and selective dataset usage to improve spectral predictions.
• It introduces external atomic databases to achieve greater computational efficiency and accuracy compared to previous versions.
• The release incorporates advanced collisional-radiative models for H- and He-like sequences, broadening its applicability in astrophysics.

Overview of "The 2017 Release of Cloudy"

"The 2017 Release of Cloudy" by G. J. Ferland et al. delineates the significant enhancements and refinements made in the Cloudy spectral synthesis code, which is utilized for simulating astrophysical environments. Notably, the paper emphasizes the transition from C13 to C17, underscoring systematic improvements in data management, model accuracy, speed, and functionality.

Key Improvements

The 2017 iteration of Cloudy introduces several notable advancements:

1. Data Management: Atomic and molecular data have been offloaded to external databases, allowing for the incorporation of extensive new datasets. This reorganization facilitates the inclusion of large datasets without compromising performance due to increased computational efficiency.
2. Dataset Utilization: Although a complete dataset immersion is infeasible in routine calculations due to resource constraints, C17 defaults to a carefully selected subset of data that substantially outperforms the previous version in predicting line emissions while maintaining computational expediency.
3. Performance and Accuracy: C17 stands out as faster than its predecessor through code optimizations, yielding more accurate results with reduced computational overhead. Examples and performance evaluations affirm C17's improvements, particularly with small models that demonstrate the boundaries of its accuracy.
4. Isoelectronic Sequences and Models: The paper elucidates advances in understanding H- and He-like isoelectronic sequences. Using complete collisional-radiative models, the authors establish density regimes for different equilibrium approximations, enhancing the code's capability in handling these complex ions.

Contributions to Astrophysics

The enhancements in Cloudy have significant implications for both theoretical and practical astrophysics:

• Enhanced Predictive Capabilities: By revising data handling and computation approaches, C17 can simulate complex astrophysical conditions more accurately, such as those involving ionized states and molecular processes.
• Broad Applicability: Cloudy continues to be a versatile tool applicable to various astrophysical phenomena, including active galaxies and interstellar medium (ISM) conditions.
• Updated Theoretical Models: The explicit revisions to isoelectronic sequences and the integration of more comprehensive databases improve the synergy between theoretical predictions and observational data.

Anticipated Developments

As computational power and atomic datasets improve, future iterations of Cloudy may see:

• Full Database Integration: With advancing hardware capabilities and efficient parallel computing, utilizing complete databases may become viable, further refining predictions.
• Expansion Beyond Current Models: Extending capability to simulate more complex ionic and molecular structures that are currently approximated could be explored.
• Improved Collaboration with Laboratory Data: Strengthening partnerships with atomic physics communities will enhance data accuracy and application breadth.

In conclusion, the 2017 release of Cloudy represents a significant step toward better understanding astrophysical environments through more precise and efficient spectral synthesis simulation. The theoretical developments and practical improvements outlined in this release enhance Cloudy's usability and accuracy, paving the way for continued advancement in computational astrophysics.