THOR: simulation support and absorption mock skewers
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THOR now reads the major galaxy formation simulation formats and generates large, flexible sets of absorption-line mock skewers.
Two recent additions make THOR substantially more useful as a general framework for synthetic observations. It can now ingest the native outputs of the most widely used galaxy formation codes, and it can generate nearly arbitrary sets of mock absorption skewers through those simulations.
From common simulation formats to one analysis framework
Galaxy formation codes represent their domains in very different ways: particles and moving meshes, adaptive mesh refinement, and a variety of code-specific snapshot formats. THOR now provides native readers and geometries for the common codes represented in the AGORA comparison suite: ART, ENZO, RAMSES, ChaNGa, GADGET-3, GEAR, GIZMO, and AREPO.
This lets the same radiative-transfer and ray-tracing workflow operate across structured and unstructured simulations without first converting every dataset into a common intermediate format.
Density fields from the eight AGORA galaxy formation codes, ingested natively and projected with THOR.
The THOR April 2026 update describes the dataset infrastructure and additional readers in more detail.
Nearly arbitrary absorption mock skewers
THOR’s new sightline operator follows each ray through the simulation cell by cell and accumulates the wavelength-dependent optical depth. The resulting spectrum retains the gas kinematics through Doppler shifts and its thermal state through line broadening.
Sightlines can be placed freely and evaluated for any ion with a Cloudy-tabulated density field. Multiple transitions can be synthesized along the same path, enabling large ensembles of matched mock spectra rather than a fixed set of projections.
One sightline through the circumgalactic medium of the AGORA z = 4 GIZMO galaxy, evaluated simultaneously in O VI, C IV, and Si IV.
The operator is designed for survey-scale mock generation. On a single GPU, THOR synthesizes millions of absorption-line skewers in minutes while retaining agreement in corresponding accuracy tests.
H I Lyman-alpha sightline throughput for THOR on GPU and CPU. See the full comparison for the benchmark setup and accuracy cross-check.
See the THOR July 2026 update for details, the sightline cookbook for the full workflow, and the absorption-line comparison for validation and benchmarks.
For the broader code architecture, radiative-transfer capabilities, and code paper, see the THOR project page.