Monte Carlo Radiative Transfer

This page explains the options for Monte Carlo radiative transfer (MCRT) simulations. The MCRT module is designed for spatially and spectrally resolved line transport and is well-suited for modeling complex environments where line photons interact with gas and dust via resonant scattering, absorption, and emission.

General MCRT Parameters

The following parameters are important MCRT parameters:

n_photons – Number of photon packets use in the simulation. [Default value: 1]
n_photons_per_star – Number of photon packets per star particle. [Optional]
n_photons_max – Maximum number of photon packets allowed when n_photons_per_star is used. [Optional]
output_stars – Flag to output the emission and escape data for each star. [Default value: false]
output_cells – Flag to output the emission and escape data for each cell. [Default value: false]
output_photons – Flag to output escaped and absorbed photon packets. [Default value: true]
photon_file – Output a separate photon file with this base name, e.g. “photons”. [Optional]
output_n_scat – Flag to output the number of scattering events for photon packets. [Compile-time parameter | Default value: false]
output_path_length – Flag to output the cumulative path length for photon packets. [Compile-time parameter | Default value: false | Output units: cm]
output_freq_length – Flag to output the cumulative frequency path length for photon packets. [Compile-time parameter | Default value: false]
output_collisions – Flag to output collisional excitation data for photons and cameras. [Default value: false]
output_source_frequency – Flag to output the emission frequency for photon packets. [Default value: false]
output_source_position – Flag to output the emission position for photon packets. [Default value: false]

Line Parameters

The following parameters are related to line specifications:

line – Name of the line to be modeled. [Default value: Lyman-alpha | Other options: Balmer-alpha, Balmer-beta, Balmer-gamma, Balmer-delta, Balmer-epsilon, Paschen-alpha, Paschen-beta, Brackett-alpha, CIII-1907-1909, CIV-1548-1550, NII-6550, NII-6585, NIII-1747-1749, NIV-1486, OI-6302, OI-6366, OII-3727-3730, OIII-1661-1666, OIII-4364, OIII-4933, OIII-4960, OIII-5008, NeIII-3969, MgII-2796-2803, SiII-1190-1193, SiII-1260, SiII-1304, SiII-1527, SiIII-1206, SiIV-1394-1403, SII-6718, SII-6733]
recoil – Include recoil induced Doppler shifting with line scattering. [Default value: true]
x_crit – Constant critical frequency for core-skipping. [Compile-time parameter | Default value: 0 | Valid range: x_crit >= 0]
dynamical_core_skipping – Non-local core-skipping for resonance lines. [Compile-time parameter | Default value: false]
n_exp_atau – Healpix exponent for the non-local \(a \tau_0\) core-skipping estimates, resulting in \(12 \times 4^{n_\text{exp,atau}}\) directions. [Default value: 0 | Valid range: n_exp_atau >= 0]
n_side_atau – Healpix number of base pixel subdivisions for the non-local \(a \tau_0\) core-skipping estimates, resulting in \(12 \times n_\text{side,atau}^2\) directions. [Overrides n_exp_atau | Default value: 1 | Valid range: n_side_atau >= 1]
p_dest – Line destruction probability between absorption and re-emission. [Default value: 0 | Valid range: 0 < p_dest < 1]
doppler_frequency – Output frequency in units of Doppler widths, otherwise as a velocity offset from line center (in units of km/s). Doppler units should only be used for idealized simulations. [Default value: false]
T_exit – Exit temperature for standardized Doppler frequency. [Default value: 1e4 | Units: K]
v_exit – Exit velocity for shifted observer frames. [Default value: (0,0,0) | Units: cm/s]
exit_wrt_com – Exit with respect to the center of mass velocity frame. [Default value: false]

Note

In what follows the units of “freq” refer to km/s unless using doppler_frequency.

Dust Parameters

The following parameters are related to dust specifications:

dust_model – Dust model for the line radiative transfer setting the dust opacity, albedo, and anisotropy parameters. [Options: SMC, MW, LAURSEN_SMC, filename]
kappa_dust – Dust opacity at the wavelength of the line, scaling the absorption coefficient by the dust mass: \(k_\text{dust} = \kappa_\text{dust} \rho_\text{dust}\) (also works for graphite kappa_dust_graphite, silicate kappa_dust_silicate, and PAH kappa_dust_PAH). [Default value: Based on dust_model and line | Units: cm^2/g of dust]
sigma_dust – Dust cross section (per metallicity) at the wavelength of the line, scaling the absorption coefficient by the hydrogen number density and metallicity: \(k_\text{dust} = \sigma_\text{dust} n_\text{H} Z\). It is generally recommended to use kappa_dust instead. [Default value: Based on dust_model and line | Units: cm^2/Z/hydrogen atom]
albedo – Dust scattering albedo defined as \(A = k_\text{scat} / (k_\text{abs} + k_\text{scat})\) (also works for graphite albedo_graphite, silicate albedo_silicate, and PAH albedo_PAH). [Default value: Based on dust_model and line | Valid range: 0 < albedo < 1]
g_dust – Anisotropy parameter \(\langle \mu \rangle\) for dust scattering (also works for graphite g_dust_graphite, silicate g_dust_silicate, and PAH g_dust_PAH). [Default value: Based on dust_model and line | Valid range: -1 < g_dust < 1]
f_ion – Survival fraction of dust in \({\rm H\,{\small II}}\) regions. [Default value: 1 | Valid range: 0 < f_ion < 1]
f_dust – Fraction of metals locked in dust grains. [Default value: 0 | Valid range: 0 < f_dust < 1]
f_PAH – Fraction of carbonaceous dust in polycyclic aromatic hydrocarbons (PAHs). [Default value: 0 | Valid range: 0 < f_PAH < 1]
T_sputter – Thermal sputtering temperature cutoff, such that no dust exists within gas hotter than this value. [Default value: 1e6 | Units: K]

Radiation Source Parameters

The following parameters are related to line radiative transfer options:

j_exp – Luminosity boosting exponent for power-law emission biasing, i.e. probabilities are rescaled according to \(\propto \mathcal{L}_\text{cell}^{j_\text{exp}}\) such that \(j_\text{exp} < 1\) can better sample lower emissivity regions. [Default value: 1 | Valid range: 0 < j_exp < 1]
V_exp – Volume boosting exponent for power-law emission biasing, i.e. probabilities are rescaled according to \(\propto V_\text{cell}^{V_\text{exp}}\) such that \(V_\text{exp} < 1\) can better sample smaller volume regions. [Default value: 1]

Gas Emission Parameters

These parameters control gas emission processes:

recombinations – Include recombination emission with luminosity \(\mathcal{L}_\text{rec} = h \nu_0 \int \alpha_\text{B,eff}(T) n_e n_\text{HII} \text{d}V\). [Default value: false]
T_floor_rec – Apply a temperature floor for the recombination rate coefficient. [Default value: 0 | Units: K]
collisions – Include collisional excitation emission with luminosity for Lyα of \(\mathcal{L}_\text{col} = h \nu_0 \int q_\text{col}(T) n_e n_\text{HI} \text{d}V\). Note: This flag works for all implemented hydrogen lines and many collisionally excited metal lines. [Default value: false]
collisions_limiter – Limit collisional excitation emission by the photoheating rate. Note: Requires collisions to be true and reads the photoheating rate from the initial conditions file. [Default value: None | Valid range: > 1]
emission_n_min – Minimum number density of emitting cells. [Default value: 0 | Units: cm^-3]
emission_n_max – Maximum number density of emitting cells. [Default value: infinity | Units: cm^-3]
emission_ne_min – Minimum electron number density of emitting cells. [Default value: 0 | Units: cm^-3]
emission_ne_max – Maximum electron number density of emitting cells. [Default value: infinity | Units: cm^-3]
cell_center_emission – Use the cell center for emission instead of uniformly sampling the cell volume. [Default value: false]

Stellar Source Parameters

These parameters define the stellar sources in the simulation:

continuum – Include stellar continuum emission around the line. [Default value: false]
continuum_range – Continuum velocity offset range for frequency sampling. [Default value: (-2000,2000) | Units: km/s]
unresolved_HII – Include unresolved HII regions in the simulation. Note: This only works for the Lyman-alpha, Balmer-alpha, and Balmer-beta lines with the conversion factors being 0.68, 0.45, and 0.12, respectively. For example, the Lyman-alpha luminosity is \(\mathcal{L}_{\text{Ly}\alpha} = 0.68 \times h \nu_0 (1 - f_\text{esc}^\text{HII}) \dot{N}_\text{ion}\). [Default value: false]
f_esc_HII – Ionizing escape fraction from unresolved HII regions, e.g. \(L_\text{Ly}\alpha = 0.68 * E_0 * (1. - f_\text{esc}^\text{HII}) \dot{N}_\text{ion}\). [Default value: 0 | Valid range: 0 < f_esc_HII < 1]
f_esc_HII_group – Use a model for the line escape fraction from unresolved HII regions based on group metallicities, e.g. \(L_\text{esc}^\text{HII} = L_\text{int} \exp(-\tau_\text{group})\). [Default value: false]
f_esc_HII_subhalo – Use a model for the line escape fraction from unresolved HII regions based on subhalo metallicities, e.g. \(L_\text{esc}^\text{HII} = L_\text{int} \exp(-\tau_\text{subhalo})\). [Default value: false]
f_esc_HII_Z0 – Normalization factor \(Z_0\) for the line escape fraction from unresolved HII regions using a power-law model of \(f_\text{esc}^\text{HII} = \exp(-\tau)\) where \(\tau = (Z/Z_0)^\beta\). [Default value: 0 | Valid range: 0 < f_esc_HII_Z0 < 1]
f_esc_HII_beta – Power-law index \(\beta\) for the line escape fraction from unresolved HII regions using a power-law model of \(f_\text{esc}^\text{HII} = \exp(-\tau)\) where \(\tau = (Z/Z_0)^\beta\). [Default value: 0.5 | Valid range: 0 < f_esc_HII_beta < 1]
source_model – Model for the stellar sources to inform continuum and unresolved_HII configurations. Note: Using certain source_model options requires reading initial stellar masses, metallicities, and ages. [Default value: “” | Options: BC03-IMF, BPASS-IMF-135-100, BPASS-CHAB-100]

Point Source Parameters

These parameters define point sources in the simulation:

point – Point source position in [x y z] format. [Optional | Units: cm]
x_point, y_point, z_point – Point source \((x, y, z)\) coordinates. [Optional | Units: cm]
L_point – Point source line luminosity. [Default value: 1 | Units: erg/s]

Plane Source Parameters

These parameters define plane sources in the simulation:

plane_direction – Direction of the plane source. [Options: ‘+x’, ‘-x’, ‘+y’, ‘-y’, ‘+z’, ‘-z’]
S_plane_cont – Plane continuum surface flux. [Optional | Units: erg/s/cm^2/angstrom]
F_plane_cont – Plane continuum source flux. [Optional | Units: erg/s/angstrom]
L_plane_cont – Plane continuum source luminosity. [Default value: 1 | Units: erg/s]
plane_beam – Use an ellipsoidal beam instead of a rectangular plane. [Default value: false]
plane_center_x_bbox, plane_center_y_bbox, plane_center_z_bbox – Center of the plane source in bounding box units. [Valid range: 0 < value < 1]
plane_radius_x_bbox, plane_radius_y_bbox, plane_radius_z_bbox – Radii of the plane source in bounding box units. [Valid range: > 0]

Sphere Source Parameters

These parameters define sphere sources in the simulation:

sphere_center_cont – Sphere center position (continuum) in [x, y, z] format. [Optional | Units: cm]
sphere_radius_cont – Sphere radius (continuum). [Optional | Units: cm]
L_sphere_cont – Sphere continuum source luminosity. [Default value: 1 | Units: erg/s]

Shell Source Parameters

These parameters define sphere sources in the simulation:

r_shell_line – Shell source radius (line emission). Note: A shell source is a spherical shell with a uniform emissivity and outward initial flux. [Optional | Units: cm]
L_shell_line – Shell line source luminosity. [Default value: 1 | Units: erg/s]
r_shell_cont – Shell radius (continuum emission). [Optional | Units: cm]
L_shell_cont – Shell continuum source luminosity. [Default value: 1 | Units: erg/s]
shell_blackbody – Set the shell luminosity based on a blackbody spectrum. [Default value: false]
T_shell – Shell blackbody temperature. [Required if shell_blackbody is true | Units: K]
r_shock – Shock source radius (continuum emission). Note: A shock source is a spherical shell with a uniform emissivity and isotropic initial flux. [Optional | Units: cm]
shock_blackbody – Set the shock luminosity based on a blackbody spectrum. [Default value: false]
T_shock – Shock blackbody temperature. [Required if shock_blackbody is true | Units: K]
L_shock – Shock source luminosity. [Default value: 1 | Units: erg/s]

Note

Stellar continuum sources should not be used simultaneously with plane, sphere, shell, or shock continuum sources.

Observed Output Parameters

This section describes the output options for MCRT simulations, including angle-averages, peel-off cameras, and directional binning parameters.

Angle-averaged Parameters

The following parameters are related to angular-averaged escape options:

output_flux_avg – Output the angle-averaged flux. [Default value: true]
output_radial_avg – Output the angle-averaged radial surface brightness. [Default value: false]
output_radial_cube_avg – Output the angle-averaged radial spectral data cube. [Default value: false]

Camera Parameters

The following parameters are related to cameras options:

n_bins – Number of frequency bins. [Default value: 100]
n_slit_bins – Number of frequency bins for slits. [Default value: n_bins]
n_cube_bins – Number of frequency bins for data cubes. [Default value: n_bins]
n_radial_cube_bins – Number of frequency bins for radial data cubes. [Default value: n_bins]
freq_range – Frequency extrema in [min max] format. Note: Similar setup for slit_freq_range, cube_freq_range, and radial_cube_freq_range. [Default value: (-1000,1000) | Units: freq]
freq_min – Frequency range minimum. Note: Similar setup for slit_freq_min, cube_freq_min, and radial_cube_freq_min. [Default value: -1000 | Units: freq]
freq_max – Frequency range maximum. Note: Similar setup for slit_freq_max, cube_freq_max, and radial_cube_freq_max. [Default value: 1000 | Units: freq]
output_fluxes – Output spectral fluxes. [Default value: true | Dimensions: (n_cameras, n_bins) | Output units: erg/s/cm^2/angstrom]
output_images – Output surface brightness images. [Default value: true | Dimensions: (n_cameras, nx_pixels, ny_pixels) | Output units: erg/s/cm^2/arcsec^2]
output_slits – Output spectral slits. [Default value: false | Dimensions: (n_cameras, n_slit_pixels, n_slit_bins) | Output units: erg/s/cm^2/arcsec^2/angstrom]
output_cubes – Output spectral data cubes. [Default value: false | Dimensions: (n_cameras, nx_cube_pixels, ny_cube_pixels, n_cube_bins) | Output units: erg/s/cm^2/arcsec^2/angstrom]
output_images2 – Output statistical moment images, e.g. to estimate convergence statistics as the relative error is approximately \(\sqrt{\text{images2}} / \text{images}\). [Default value: false | Dimensions: (n_cameras, nx_pixels, ny_pixels) | Output units: erg^2/s^2/cm^4/arcsec^4]
output_radial_images – Output radial surface brightness images. [Default value: false | Dimensions: (n_cameras, n_radial_pixels) | Output units: erg/s/cm^2/arcsec^2]
output_radial_cubes – Output radial spectral data cubes. [Default value: false | Dimensions: (n_cameras, n_radial_cube_pixels, n_radial_cube_bins) | Output units: erg/s/cm^2/arcsec^2/angstrom]
output_radial_images2 – Output statistical moment radial images, e.g. to estimate convergence statistics as the relative error is approximately \(\sqrt{\text{radial\_images2}} / \text{radial\_images}\). [Default value: false | Dimensions: (n_cameras, n_radial_pixels) | Output units: erg^2/s^2/cm^4/arcsec^4]

The following parameters produce intrinsic or attenuation only images:

output_mcrt_emission – Output intrinsic emission without transport based on MCRT sampling (also works for radial images). [Default value: false | Dimensions: (n_cameras, nx_pixels, ny_pixels) | Output units: erg/s/cm^2/arcsec^2]
output_mcrt_attenuation – Output attenuated emission without scattering based on MCRT sampling (also works for radial images). [Default value: false | Dimensions: (n_cameras, nx_pixels, ny_pixels) | Output units: erg/s/cm^2/arcsec^2]
output_proj_emission – Output intrinsic emission without transport with ray-based imaging. [Default value: false | Dimensions: (n_cameras, nx_pixels, ny_pixels) | Output units: erg/s/cm^2/arcsec^2]
output_proj_attenuation – Output attenuated emission without scattering with ray-based imaging. [Default value: false | Dimensions: (n_cameras, nx_pixels, ny_pixels) | Output units: erg/s/cm^2/arcsec^2]
output_proj_cube_emission – Output intrinsic emission without transport with ray-based imaging. [Default value: false | Dimensions: (n_cameras, nx_cube_pixels, ny_cube_pixels, n_cube_bins) | Output units: erg/s/cm^2/arcsec^2/angstrom]
output_proj_cube_attenuation – Output attenuated emission without scattering with ray-based imaging. [Default value: false | Dimensions: (n_cameras, nx_cube_pixels, ny_cube_pixels, n_cube_bins) | Output units: erg/s/cm^2/arcsec^2/angstrom]

Note

The intrinsic and attenuation only images do not require scattering. Therefore, the projection outputs are preferred as they employ a ray-based quadtree imaging method for a noiseless solution with adaptive spatial convergence.

The following parameters produce spatially integrated camera frequency moments [Dimensions: n_cameras]:

output_escape_fractions – Output camera escape fractions. [Default value: true]
output_freq_avgs – Output camera frequency averages. [Default value: false | Output units: freq]
output_freq_stds – Output frequency standard deviations. [Default value: false | Output units: freq]
output_freq_skews – Output frequency skewnesses. [Default value: false]
output_freq_kurts – Output frequency kurtoses. [Default value: false]

The following parameters produce camera frequency moments for each image pixel [Dimensions: (n_cameras, nx_pixels, ny_pixels)]:

output_freq_images – Output average frequency images. [Default value: false | Output units: freq]
output_freq2_images – Output frequency^2 images. [Default value: false | Output units: freq^2]
output_freq3_images – Output frequency^3 images. [Default value: false | Output units: freq^3]
output_freq4_images – Output frequency^4 images. [Default value: false | Output units: freq^4]

The following parameters produce camera frequency moments for each radial image pixel [Dimensions: (n_cameras, n_radial_pixels)]:

output_freq_radial_images – Output average frequency radial images. [Default value: false | Output units: freq]
output_freq2_radial_images – Output frequency^2 radial images. [Default value: false | Output units: freq^2]
output_freq3_radial_images – Output frequency^3 radial images. [Default value: false | Output units: freq^3]
output_freq4_radial_images – Output frequency^4 radial images. [Default value: false | Output units: freq^4]

The following parameters are useful for on-the-fly false color imaging:

output_rgb_images – Output flux-weighted frequency RGB images. Note: The normalized image log intensity can be used as the alpha opacity of the image to give a nice illustration of the spectral data cube. [Default value: false | Dimensions: (n_cameras, nx_pixels, ny_pixels, 3) | Output units: RGB color]
output_rgb_radial_images – Output flux-weighted frequency RGB radial images. [Default value: false | Dimensions: (n_cameras, n_radial_pixels, 3) | Output units: RGB color]
output_rgb_map – Output flux-weighted frequency RGB Healpix map. [Default value: false | Dimensions: (12 * n_side_map^2, 3) | Output units: RGB color]
rgb_freq_range – Frequency extrema in [min max] format. [Default value: (-1000,1000) | Units: freq]
rgb_freq_min – Frequency range minimum. [Default value: -1000 | Units: freq]
rgb_freq_max – Frequency range maximum. [Default value: 1000 | Units: freq]
adjust_camera_frequency – Adjust frequencies for each camera based on offsets from a file. Note: This was implemented to center the RGB and other cameras for Lyα on the Hα line center. Thus, the file must have a dataset called “freq_avgs” of length n_cameras. [Default value: false]
freq_offset_file – Frequency offset file (optional). [Default value: init_file]
freq_offset_dir – Frequency offset directory (optional). [Default value: init_dir]
freq_offset_base – Frequency offset file base (optional). [Default value: init_base]
freq_offset_ext – Frequency offset file extension (optional). [Default value: hdf5]

Healpix Binning Parameters

The following parameters are related to line-of-sight healpix binning options:

n_exp_map – Healpix exponent for the line-of-sight map, resulting in \(12 \times 4^{n_\text{exp,map}}\) directions. Note: Similar setup for n_exp_flux, n_exp_radial, and n_exp_cube. [Default value: 2 | Valid range: n_exp_map >= 0]
n_side_map – Healpix number of base pixel subdivisions for the line-of-sight map, resulting in \(12 \times n_\text{side,map}^2\) directions. Note: Similar setup for n_side_flux, n_side_radial, and n_side_cube. [Overrides n_exp_map | Default value: 4 | Valid range: n_side_map >= 1]
n_map_bins – Number of frequency bins for the line-of-sight flux map. Note: Similar setup for n_cube_map_bins. [Default value: 100]
map_freq_range – Frequency extrema in [min max] format for the line-of-sight flux map. Note: Similar setup for cube_map_freq_range. [Default value: (-1000,1000) | Units: freq]
map_freq_min – Frequency range minimum for the line-of-sight flux map. Note: Similar setup for cube_map_freq_min. [Default value: -1000 | Units: freq]
map_freq_max – Frequency range maximum for the line-of-sight flux map. Note: Similar setup for cube_map_freq_max. [Default value: 1000 | Units: freq]
map_radius – Radius for the line-of-sight healpix map of radial surface brightness images. Note: Similar setup for cube_map_radius. [Units: cm]
map_radius_bbox – Radius for the line-of-sight healpix map of radial surface brightness images in units of the bounding box radius \(R_{\rm box}\). Note: Similar setup for cube_map_radius_bbox. [Units: bounding box]
map_radius_Rvir – Radius for the line-of-sight healpix map of radial surface brightness images in units of the selected halo virial radius \(R_{\rm vir}\). Note: Similar setup for cube_map_radius_Rvir. [Units: Virial radius]
n_map_pixels – Number of radial pixels for the line-of-sight healpix map of radial surface brightness images. Note: Similar setup for n_cube_map_pixels. [Default value: 100]
map_pixel_width – Intrinsic width of each radial pixel for the line-of-sight healpix map of radial surface brightness images. Note: Similar setup for cube_map_pixel_width. [Units: cm]
map_pixel_arcsec – Observed angular width of each radial pixel for the line-of-sight healpix map of radial surface brightness images. Note: Similar setup for cube_map_pixel_arcsec. [Units: arcseconds]
output_map – Output a line-of-sight healpix map of escape fractions. [Default value: false | Dimensions: (12 * n_side_map^2)]
output_map2 – Output a statistical moment line-of-sight healpix map, e.g. to estimate convergence statistics as the relative error is approximately \(\sqrt{\text{map2}} / \text{map}\). [Default value: false | Dimensions: (12 * n_side_map^2)]
output_flux_map – Output a line-of-sight healpix map of spectral fluxes. [Default value: false | Dimensions: (12 * n_side_flux^2, n_map_bins) | Output units: erg/s/cm^2/angstrom]
output_radial_map – Output a line-of-sight healpix map of radial surface brightness images. [Default value: false | Dimensions: (12 * n_side_radial^2, n_map_pixels) | Output units: erg/s/cm^2/arcsec^2]
output_cube_map – Output a line-of-sight healpix map of radial spectral data cubes. [Default value: false | Dimensions: (12 * n_side_cube^2, n_cube_map_pixels, n_cube_map_bins) | Output units: erg/s/cm^2/arcsec^2/angstrom]

The following parameters produce frequency moments for each Healpix map pixel [Dimensions: 12 * n_side_map^2]:

output_freq_map – Output average frequency map. [Default value: false | Output units: freq]
output_freq2_map – Output frequency^2 map. [Default value: false | Output units: freq^2]
output_freq3_map – Output frequency^3 map. [Default value: false | Output units: freq^3]
output_freq4_map – Output frequency^4 map. [Default value: false | Output units: freq^4]

Angular Binning Parameters

The following parameters are related to line-of-sight angular cosine (\(\mu=\cos\theta\)) binning options:

n_mu – Number of directional bins for the line-of-sight \(\mu\) map. Note: Similar setup for n_mu_flux. [Default value: 100]
n_mu_bins – Number of frequency bins for the line-of-sight flux \(\mu\) map. [Default value: 100]
mu_freq_range – Frequency extrema in [min max] format for the line-of-sight flux \(\mu\) map. [Default value: (-1000,1000) | Units: freq]
mu_freq_min – Frequency range minimum for the line-of-sight flux \(\mu\) map. [Default value: -1000 | Units: freq]
mu_freq_max – Frequency range maximum for the line-of-sight flux \(\mu\) map. [Default value: 1000 | Units: freq]
output_mu – Output a line-of-sight \(\mu\) map of escape fractions. [Default value: false | Dimensions: n_mu)]
output_mu2 – Output statistical moment line-of-sight \(\mu\) map, e.g. to estimate convergence statistics as the relative error is approximately \(\sqrt{\text{map2}} / \text{map}\). [Default value: false | Dimensions: n_mu)]
output_flux_mu – Output a line-of-sight \(\mu\) map of spectral fluxes. [Default value: false | Dimensions: (n_mu, n_mu_bins) | Output units: erg/s/cm^2/angstrom]

The following parameters produce frequency moments for each \(\mu\) map [Dimensions: n_mu]:

output_freq_mu – Output average frequency \(\mu\) map. [Default value: false | Output units: freq]
output_freq2_mu – Output frequency^2 \(\mu\) map. [Default value: false | Output units: freq^2]
output_freq3_mu – Output frequency^3 \(\mu\) map. [Default value: false | Output units: freq^3]
output_freq4_mu – Output frequency^4 \(\mu\) map. [Default value: false | Output units: freq^4]

Radial Flow Parameters

The radial flow data is a 3D probe of the radiation field. The output data is in the radial_flow group with an attribute n_radial_bins and fields radial_edges [cm] (radial bin edges), L_src (emission as a function of source radii), L_esc (escape as a function of source radii), L_abs (absorption as a function of absorption radii), L_pass (first passage by source radii and shell boundaries), and L_flow (net flux by source radii and shell boundaries).

The following parameters are compile-time options and need to be set in the defines.yaml file:

output_radial_flow – Output radial flow data. [Compile-time parameter | Default value: false]
output_group_flows – Output group flow data. [Compile-time parameter | Default value: false]
output_subhalo_flows – Output subhalo flow data. [Compile-time parameter | Default value: false]

The associated runtime parameters are:

radial_linspace_pc – Radial linear-spaced binning in parsecs for radial flow data as [min max n_edges]. [Default value: 1 | Units: pc]
radial_logspace_pc – Radial log-spaced binning in parsecs for radial flow data as [log_min log_max n_edges]. [Default value: 1 | Units: pc]
radial_linspace_Rvir – Radial linear-spaced binning in units of the selected halo virial radius \(R_{\rm vir}\) for radial flow data as [min max n_edges]. [Default value: 1 | Units: Virial radius]
radial_logspace_Rvir – Radial log-spaced binning in units of the selected halo virial radius \(R_{\rm vir}\) for radial flow data as [log_min log_max n_edges]. [Default value: 1 | Units: Virial radius]
radial_edges_pc – Radial edges in parsecs for radial flow data. Note: Similar config for radial_edges_Rvir and radial_edges_cm. [Default value: 1 | Units: pc]

Advanced Parameters

The following parameters are related to advanced options:

two_level_atom – Line radiative transfer incorporates occupation number densities from both lower and upper transitions. If this is false then we assume that bound electrons are always in the ground state. Note: This currently also switches from a Voigt to a Gaussian line profile, and assumes complete redistribution for scattering. [Default value: false]
spontaneous – Include spontaneous emission in two_level_atom line transfer as \(\mathcal{L}_\text{sp} = h c A_{21} \int n_2 \text{d}V\). [Default value: false]
resonant_scattering – Turn resonant scattering on/off. Note: It is not recommended to override this option unless you know exactly what you are doing. [Default value: Based on line]
anisotropic_scattering – Flag to turn anisotropic scattering on or off (in the core of the line only). [Default value: true for Lyman-alpha, false for other lines]
load_balancing – Use MPI load balancing algorithms. Note: Due to the OpenMP load balancing this is not recommended in general as the number of MPI tasks is usually much smaller than the number of photon packets. [Default value: false]