Fields

Fields are named quantities attached to particles (position, density, temperature, derived values like emissivities). They are lazily evaluated and cached: computed once when first requested.

Particle Types

Type	Contents
`PartType0`	Gas cells
`PartType1`	Dark matter
`PartType4`	Stars
`Group`	FOF groups
`Subhalo`	Subhalos

Gas Fields (PartType0)

Core Fields

Field	Description	Units
`PositionX`, `PositionY`, `PositionZ`	Normalized position	boxunits [0,1)
`VelocityX`, `VelocityY`, `VelocityZ`	Velocity components	km/s
`VelocityMagnitude`	Speed	km/s
`Temperature`	Gas temperature	K
`Volume`	Cell volume	code units
`MaxDist`	Approximate cell radius	boxunits

Hydrogen Fields

Field	Description	Units
`HIdensity`	Neutral hydrogen number density (nHI)	cm⁻³
`HIIdensity`	Ionized hydrogen number density (nHII)	cm⁻³
`HIIMasses`	Ionized hydrogen mass	code units
`TotalHydrogenMasses`	Total hydrogen mass	code units
`NumberDensity`	Number density (assumes μ=0.6)	cm⁻³

Lyman-alpha Fields

Field	Description	Units
`Lya_recB_emissivity`	Emissivity from recombinations	erg/s/cm³
`Lya_collexc_emissivity`	Emissivity from collisional excitations	erg/s/cm³
`Lya_recB`	Luminosity from recombinations	erg/s
`Lya_collexc`	Luminosity from collisional excitations	erg/s

Metallicity Fields

Field	Description
`MetallicityMasses`	Metallicity in mass units
`GFM_Metals_H`, `GFM_Metals_He`, ...	Individual element mass fractions

Cloudy Fields

When Cloudy tables are loaded, additional fields become available:

Pattern	Description	Units
`cloudyemission_<line>`	Line emissivity	erg/s/cm³
`cloudyemission_<line>_times_volume`	Line luminosity	erg/s
`cloudyabsorption_<line>`	Absorption coefficient	cm⁻¹
`cloudydensity_<ion>`	Ion number density	cm⁻³

Lines and ions are auto-detected from loaded tables.

Stellar Fields (PartType4)

Field	Description	Units
`StellarAge`	Age since formation	Gyr
`StellarMetallicityMasses`	Metallicity in mass units	code units
`InitialStellarMasses`	Mass at formation	code units
`VelocityMagnitude`	Speed	km/s

Dark Matter Fields (PartType1)

Field	Description	Units
`DMDensity`	Density (or mass if unavailable)	code units
`VelocityMagnitude`	Speed	km/s

Catalog Fields

Group

Field	Description	Units
`PositionX`, `PositionY`, `PositionZ`	FOF group center	boxunits [0,1)

Subhalo

Field	Description	Units
`PositionX`, `PositionY`, `PositionZ`	Subhalo center	boxunits [0,1)

Using Fields

Fields are referenced by name in configuration. Example in raytracer config:

raytracer:
  emission_field: Lya_recB_emissivity
  absorption_field: HIdensity

See Field Filters for applying conditions and transforms to fields.