Datasets

Thor provides several dataset types that define the geometry and basic gas properties for a simulation.
You select one via dataset_type and then add a matching top‑level section in the YAML file.

Overview

See also: Configuration Reference for global options.

Spherical Shell (shellmodel)

Spherically symmetric shell centered in the unit cube, with inner/outer radius in box units.

dataset_type: 'shellmodel'

shellmodel:
  boxsize: 3.086e21       # cm (physical box size)
  inner_radius: 0.0       # 0.0–0.5, in box units
  outer_radius: 0.1       # 0.0–0.5, in box units
  temperature: 20000.0    # K
  density: 0.078098       # cm^-3 (optional, see below)
  outflow_velocity: 0.0   # cm/s, value at r = outer_radius

Key points:

• inner_radius, outer_radius are fractions of the box size, limited to [0, 0.5] and must satisfy inner_radius < outer_radius.

• Gas density can be set in three equivalent ways (pick exactly one):

  • density (volume density in cm⁻³),
  • column_density (cm⁻²) together with boxsize,
  • log_NHI (log10 of column density in cm⁻²).

• Temperature can be given directly via temperature or derived from an effective cross‑section using:

  • sigma (line‑center cross‑section; requires the emission line from the driver).

• Dust‑related parameters exist but the current shell implementation initializes dust absorption to zero.

Power‑Law Shell (powerlaw_shellmodel)

Shell with power‑law profiles for density and velocity, building on the same basic parameters as shellmodel.

dataset_type: 'powerlaw_shellmodel'

powerlaw_shellmodel:
  boxsize: 3.086e21
  inner_radius: 0.01
  outer_radius: 0.1
  temperature: 20000.0
  density: 0.078098              # interpreted as mean density

  # Velocity profile v(r) ∝ r^powerlaw_index_velocity
  outflow_velocity: 200e5        # cm/s at r = outer_radius (simple case)
  powerlaw_index_velocity: 1.0

  # Density profile ρ(r) ∝ r^powerlaw_index_density
  powerlaw_index_density: -2.0
  conserve_column_density: true  # renormalize density to match shell column

Key points:

• All shellmodel density/temperature options are available and interpreted as averages before applying the power law.
• powerlaw_index_velocity and powerlaw_index_density control the radial scalings.
• If conserve_column_density: true, the code rescales density so that the line‑of‑sight column matches the corresponding uniform shell.
• Advanced velocity options:
• velocity_ratio: ratio between maximum and minimum velocity; used to infer an effective inner radius (see code comments).
• outflow_velocity_*average: alternative ways to specify the velocity scale; only one of these (or outflow_velocity from the shell) should be used.

Uniform Grid (unigrid)

Cartesian grid with optional domain decomposition and several initialization “loaders”.

dataset_type: 'unigrid'

unigrid:
  ngrid: 64               # cells per dimension (global)
  loader: sphere          # 'sphere', 'cylinder', or 'gadget'
  boxsize: 3.086e21       # cm, required if not implied by the loader

  # Optional: domain decomposition (see configuration.md)
  # domain: [[0.0, 1.0], [0.0, 1.0], [0.0, 1.0]]
  # local_domain_pad: 0.03

Loader: sphere

unigrid:
  ngrid: 64
  loader: sphere
  sphere:
    radius: 0.1           # in box units by default
    density: 0.078098     # cm^-3
    temperature: 20000.0  # K
    velocity: [1.0e5, 0.0, 0.0]  # optional: uniform velocity [vx, vy, vz] in cm/s
    relative_distances: true  # if false, radius is interpreted in physical units

Loader: cylinder (unused/test)

Primarily used for internal/regression tests; not used in shipped example configurations.

unigrid:
  ngrid: 64
  loader: cylinder
  cylinder:
    radius: 0.1           # in box units
    height: 0.5           # extent along x in box units
    density: 0.078098
    temperature: 20000.0

Loader: gadget

Interpolates a Gadget snapshot onto the grid.

unigrid:
  ngrid: 64
  loader: gadget
  gadget:
    path: "./snapdir_099"        # Gadget snapshot root
    interpolator: "ngp"          # 'ngp' (default) or 'sph' (work‑in‑progress)
    boxsize: 1.0e23              # cm, optional override of Gadget header
    pregridded_path: ""          # optional: read pre‑gridded HDF5 instead
    domain_consistency_check: true

Additional options:

• fields: list of field names to load (case‑insensitive, defaults to density/temperature/velocity for MCRT).
• When pregridded_path is non‑empty, the code loads data from that HDF5 file instead of performing interpolation.
• Distributed runs use domain and local_domain_pad from the dataset section, and pbc from the driver, via the common dataset interface.

Infinite Slab (infiniteslab)

One‑dimensional slab along the z‑axis, infinite in x and y (implemented as a single cell in z with special boundary handling).

dataset_type: 'infiniteslab'

infiniteslab:
  boxsize: 3.086e21      # cm
  temperature: 20000.0   # K

  # choose exactly one of:
  density: 0.078098      # cm^-3
  # tau: 1.0             # optical depth (requires emission line)

  # dust (optional)
  tau_dust: 0.0          # effective dust optical depth across half the slab
  density_fluff: 0.0     # density outside the slab (currently unused in main loop)

Key points:

• Exactly one of density or tau must be specified (the helper enforces a single choice among density, column_density, tau; for slabs column_density is currently not supported and will error if > 0).
• If tau is used, the code derives density from the line cross‑section and boxsize (requires a valid emission line in the driver).
• tau_dust sets a constant dust absorption coefficient inside the slab.

Point Cloud (pointcloud_voronoi and variants)

Voronoi tessellation of particles, typically from a Gadget simulation.

dataset_type: 'pointcloud_voronoi'

pointcloud_voronoi:
  hilbert_bits: 8            # 1–10, controls spatial indexing resolution
  loader: "gadget"

  gadget:
    path: "./snapdir_099"                # Gadget snapshot root
    catalog_path: "./groups_099"         # FOF/subfind catalog (required for zoom_target)
    fields: ["PositionX", "PositionY", "PositionZ", "Temperature", "Density"]
    zoom_target:
      hid: 0                             # Halo ID (0 = most massive)
      rvir: 2.5                          # Cutout radius in multiples of virial radius
    # zoom_box: [[xmin, xmax], [ymin, ymax], [zmin, zmax]]  # alternative to zoom_target

  # Optional: Cloudy ionization/emission tables
  cloudy:
    enabled: true
    emission_table_path: "/path/to/grid_emissivities.hdf5"
    ion_table_path: "/path/to/grid_ions.hdf5"
    redshift_interp: true
    interpolation_order: 1

Key points:

• Supported variants (same YAML structure, different interpolator under the hood):

  • pointcloud_voronoi (default, experimental)
  • pointcloud_voronoi_tree (tree‑accelerated, do not use)
  • pointcloud_voronoi_approx (approximate Voronoi, do not use)
  • pointcloud_sph (SPH‑style interpolation, do not use)

• hilbert_bits controls the resolution of the Hilbert grid used to accelerate neighbor lookups (must be between 1 and 10).

• Currently, only the gadget loader is supported; it uses the same field naming as the unigrid Gadget loader and adds extra fields as needed for the chosen emission line.
• Voronoi construction‑specific options are configured under a construction: subsection and documented in detail here.

Gadget Loader Options

Zoom Configuration

The Gadget loader supports two mutually exclusive ways to define a spatial cutout. You must use exactly one — specifying both will produce an error.

Option A: zoom_target — halo-centric cutout (requires catalog_path):

Internally, zoom_target is converted to a zoom_box centered on the halo position with half-width rvir * R_vir.

Option B: zoom_box — explicit bounding box in normalized coordinates [0, 1]:

zoom_box: [[0.45, 0.55], [0.45, 0.55], [0.45, 0.55]]

zoom_box can be placed either under the gadget: subsection or at the dataset level.

Cloudy Tables

When cloudy.enabled: true, Thor loads pre-computed Cloudy ionization and emission grids to derive line emissivities and absorption coefficients from the gas properties.