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The SKIRT project
advanced radiative transfer for astrophysics
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The SKIRT project
advanced radiative transfer for astrophysics
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#include <SpinFlipAbsorptionMix.hpp>
Public Member Functions | |
| double | defaultTemperature () const |
| bool | hasExtraSpecificState () const override |
| double | indicativeTemperature (const MaterialState *state, const Array &Jv) const override |
| void | initializeSpecificState (MaterialState *state, double metallicity, double temperature, const Array ¶ms) const override |
| double | mass () const override |
| MaterialType | materialType () const override |
| double | opacityAbs (double lambda, const MaterialState *state, const PhotonPacket *pp) const override |
| double | opacityExt (double lambda, const MaterialState *state, const PhotonPacket *pp) const override |
| double | opacitySca (double lambda, const MaterialState *state, const PhotonPacket *pp) const override |
| void | peeloffScattering (double &I, double &Q, double &U, double &V, double &lambda, Direction bfkobs, Direction bfky, const MaterialState *state, const PhotonPacket *pp) const override |
| void | performScattering (double lambda, const MaterialState *state, PhotonPacket *pp) const override |
| double | sectionAbs (double lambda) const override |
| double | sectionExt (double lambda) const override |
| double | sectionSca (double lambda) const override |
| vector< StateVariable > | specificStateVariableInfo () const override |
 Public Member Functions inherited from MaterialMix | |
| virtual double | asymmpar (double lambda) const |
| virtual Array | emissionSpectrum (const MaterialState *state, const Array &Jv) const |
| virtual DisjointWavelengthGrid * | emissionWavelengthGrid () const |
| virtual Array | emissivity (const Array &Jv) const |
| virtual bool | hasContinuumEmission () const |
| virtual DynamicStateType | hasDynamicMediumState () const |
| virtual bool | hasExtraSpecificState () const |
| virtual bool | hasLineEmission () const |
| virtual bool | hasNegativeExtinction () const |
| virtual bool | hasPolarizedAbsorption () const |
| virtual bool | hasPolarizedEmission () const |
| virtual bool | hasPolarizedScattering () const |
| virtual bool | hasResonantScattering () const |
| virtual bool | hasScatteringDispersion () const |
| virtual bool | hasStochasticDustEmission () const |
| virtual double | indicativeTemperature (const MaterialState *state, const Array &Jv) const |
| virtual void | initializeSpecificState (MaterialState *state, double metallicity, double temperature, const Array ¶ms) const |
| bool | isDust () const |
| bool | isElectrons () const |
| bool | isGas () const |
| virtual bool | isSpecificStateConverged (int numCells, int numUpdated, int numNotConverged, MaterialState *currentAggregate, MaterialState *previousAggregate) const |
| virtual Array | lineEmissionCenters () const |
| virtual Array | lineEmissionMasses () const |
| virtual Array | lineEmissionSpectrum (const MaterialState *state, const Array &Jv) const |
| virtual double | mass () const =0 |
| virtual MaterialType | materialType () const =0 |
| virtual double | opacityAbs (double lambda, const MaterialState *state, const PhotonPacket *pp) const =0 |
| virtual double | opacityExt (double lambda, const MaterialState *state, const PhotonPacket *pp) const =0 |
| virtual double | opacitySca (double lambda, const MaterialState *state, const PhotonPacket *pp) const =0 |
| virtual vector< SnapshotParameter > | parameterInfo () const |
| virtual void | peeloffScattering (double &I, double &Q, double &U, double &V, double &lambda, Direction bfkobs, Direction bfky, const MaterialState *state, const PhotonPacket *pp) const =0 |
| virtual void | performScattering (double lambda, const MaterialState *state, PhotonPacket *pp) const =0 |
| virtual double | sectionAbs (double lambda) const =0 |
| virtual double | sectionExt (double lambda) const =0 |
| virtual const Array & | sectionsAbs (double lambda) const |
| virtual const Array & | sectionsAbspol (double lambda) const |
| virtual double | sectionSca (double lambda) const =0 |
| virtual vector< StateVariable > | specificStateVariableInfo () const =0 |
| virtual const Array & | thetaGrid () const |
| virtual UpdateStatus | updateSpecificState (MaterialState *state, const Array &Jv) const |
| Public Member Functions inherited from SimulationItem | |
| template<class T > | |
| T * | find (bool setup=true) const |
| template<class T > | |
| T * | interface (int levels=-999999, bool setup=true) const |
| virtual string | itemName () const |
| void | setup () |
| string | typeAndName () const |
| Public Member Functions inherited from Item | |
| Item (const Item &)=delete | |
| virtual | ~Item () |
| void | addChild (Item *child) |
| const vector< Item * > & | children () const |
| virtual void | clearItemListProperty (const PropertyDef *property) |
| void | destroyChild (Item *child) |
| virtual bool | getBoolProperty (const PropertyDef *property) const |
| virtual vector< double > | getDoubleListProperty (const PropertyDef *property) const |
| virtual double | getDoubleProperty (const PropertyDef *property) const |
| virtual string | getEnumProperty (const PropertyDef *property) const |
| virtual int | getIntProperty (const PropertyDef *property) const |
| virtual vector< Item * > | getItemListProperty (const PropertyDef *property) const |
| virtual Item * | getItemProperty (const PropertyDef *property) const |
| virtual string | getStringProperty (const PropertyDef *property) const |
| int | getUtilityProperty (string name) const |
| virtual void | insertIntoItemListProperty (const PropertyDef *property, int index, Item *item) |
| Item & | operator= (const Item &)=delete |
| Item * | parent () const |
| virtual void | removeFromItemListProperty (const PropertyDef *property, int index) |
| virtual void | setBoolProperty (const PropertyDef *property, bool value) |
| virtual void | setDoubleListProperty (const PropertyDef *property, vector< double > value) |
| virtual void | setDoubleProperty (const PropertyDef *property, double value) |
| virtual void | setEnumProperty (const PropertyDef *property, string value) |
| virtual void | setIntProperty (const PropertyDef *property, int value) |
| virtual void | setItemProperty (const PropertyDef *property, Item *item) |
| virtual void | setStringProperty (const PropertyDef *property, string value) |
| void | setUtilityProperty (string name, int value) |
| virtual string | type () const |
Protected Member Functions | |
| SpinFlipAbsorptionMix () | |
| Protected Member Functions inherited from MaterialMix | |
| MaterialMix () | |
| Configuration * | config () const |
| Random * | random () const |
| void | setupSelfBefore () override |
| Protected Member Functions inherited from SimulationItem | |
| SimulationItem () | |
| virtual bool | offersInterface (const std::type_info &interfaceTypeInfo) const |
| virtual void | setupSelfAfter () |
| virtual void | setupSelfBefore () |
| Protected Member Functions inherited from Item | |
| Item () | |
Private Types | |
| using | BaseType = MaterialMix |
| using | ItemType = SpinFlipAbsorptionMix |
Private Attributes | |
| double | _defaultTemperature |
Friends | |
| class | ItemRegistry |
Additional Inherited Members | |
| Public Types inherited from MaterialMix | |
| enum class | DynamicStateType { None , Primary , Secondary , PrimaryIfMergedIterations } |
| enum class | MaterialType { Dust , Electrons , Gas } |
The SpinFlipAbsorptionMix class describes the material properties related to the 21 cm spin-flip transition in neutral atomic hydrogen, including only absorption (i.e. omitting emission processes). The 21 cm opacity in a given cell is determined from gas properties defined in the input model (gas temperature).
Configuring the simulation
Simulations of 21 cm the spin-flip transition usually include 21 cm emission (see the SpinFlipSEDFamily class) in addition to a medium component configured with the spin flip material mix (this class). Hence, the simulation mode should be set to "ExtinctionOnly".
As the opacity of the 21 cm line depends on the gas temperature as well as the neutral atomic hydrogen density \(n_\mathrm{HI}\), this information is read from an input file by associating the SpinFlipAbsorptionMix with a subclass of ImportedMedium. For that medium component, the ski file attribute importTemperature must be set to 'true', and importMetallicity and importVariableMixParams must be left at 'false'. For example, if bulk velocities are also imported for this medium component (i.e. importVelocity is 'true'), the column order would be
\[ ..., T, v_\mathrm{x}, v_\mathrm{y}, v_\mathrm{z} \]
For basic testing purposes, the SpinFlipAbsorptionMix can also be associated with a geometric medium component. The geometry then defines the spatial density distribution (i.e. \(n_\mathrm{HI}\)), and this class offers a configuration property to specify a fixed default temperature value that will be used across the spatial domain.
Absorption
Following Draine 2011 Chapter 8, and substituting wavelengths for frequencies, the monochromatic absorption cross section per neutral hydrogen atom \(\varsigma(\lambda)\) at frequency \(\lambda\) can be written as
\[\varsigma^\text{abs}(\lambda) = \frac{3}{32\pi}\,A_\mathrm{SF}\,\frac{hc \,\lambda_\mathrm{SF}} {k_\mathrm{B}T_\mathrm{s}} \times \frac{\lambda_\mathrm{SF}} {\sqrt{2\pi}\,\sigma} \,\exp\left(-\frac{u^2(\lambda)} {2\sigma^2}\right) \]
where \(T_\mathrm{s}\) is the spin temperature of the hydrogen gas (see below), \(\sigma=\sqrt{k_B T/m_\mathrm{p}}\) is the velocity dispersion corresponding to the thermal motion of the atoms, and \(u(\lambda)=c(\lambda-\lambda_\mathrm{SF})/\lambda\) is the frequency deviation from the line center in velocity units.
According to Kim, Ostriker and Kim 2014 (ApJ 786:64), the spin temperature \(T_\mathrm{s}\) is essentially equal to the kinetic gas temperature \(T\) for low gas temperatures \(T<1000~\mathrm{K}\). For higher gas temperatures, it also depends on other gas properties, with an upper bound that never exceeds a fixed maximum value, i.e. \(T_\mathrm{s,upper} \lesssim 5000~\mathrm{K}\) (see their Figure 2).
To avoid the need for defining additional gas properties in the input model, we here use an approximate upper bound for the spin temperature given by
\[ T_\mathrm{s}= 6000~\mathrm{K} \times \left( 1-\mathrm{e}^{-T/5000~\mathrm{K} } \right).\]
Because the absorption cross section is inversely proportional to the spin temperature, this yields an approximate lower bound for the cross section.
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inlineprotected |
Default constructor for concrete Item subclass SpinFlipAbsorptionMix : "A gas mix supporting the spin-flip 21 cm hydrogen absorption" .
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inline |
This function returns the value of the discoverable double property defaultTemperature : "the default temperature of the gas" .
This property represents a physical quantity of type "temperature" .
The minimum value for this property is "[3" .
The maximum value for this property is "1e9]" .
The default value for this property is given by the conditional value expression "1e4" .
This property is displayed only if the Boolean expression "Level2" evaluates to true after replacing the names by true or false depending on their presence.
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overridevirtual |
This function returns true, indicating that the cross sections returned by this material mix depend on the values of specific state variables other than the number density.
Reimplemented from MaterialMix.
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overridevirtual |
This function returns an indicative temperature of the material mix when it would be embedded in a given radiation field. The implementation in this class ignores the radiation field and returns the temperature stored in the specific state for the relevant spatial cell and medium component. Because the hydrogen temperature is not calculated self-consistently in our treatment, this value corresponds to the temperature defined by the input model at the start of the simulation.
Reimplemented from MaterialMix.
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overridevirtual |
This function initializes the specific state variables requested by this material mix through the specificStateVariableInfo() function except for the number density. For this class, the function initializes the temperature to the specified imported value, or if not available, to the user-configured default value.
Reimplemented from MaterialMix.
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overridevirtual |
This function returns the mass of a neutral hydrogen atom.
Implements MaterialMix.
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overridevirtual |
This function returns the fundamental material type represented by this material mix, which is MaterialType::Gas.
Implements MaterialMix.
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overridevirtual |
This function returns the 21 cm absorption opacity \(k^\text{abs}= n_mathrm{HI} \varsigma^\text{abs}\) for the given wavelength and material state. The photon packet properties are not used.
Implements MaterialMix.
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overridevirtual |
This function returns the 21 cm extinction opacity \(k^\text{ext}=k^\text{abs}\) for the given wavelength and material state, which equals the absorption opacity because the scattering opacity is zero. The photon packet properties are not used.
Implements MaterialMix.
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overridevirtual |
This function returns the 21 cm scattering opacity \(k^\text{sca}\) which is trivially zero at all wavelengths.
Implements MaterialMix.
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overridevirtual |
This function does nothing because the 21 cm line does not scatter.
Implements MaterialMix.
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overridevirtual |
This function does nothing because the 21 cm line does not scatter.
Implements MaterialMix.
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overridevirtual |
This function returns the 21 cm absorption cross section per neutral hydrogen atom at the given wavelength and using the default gas properties configured for this material mix.
Implements MaterialMix.
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overridevirtual |
This function returns the total 21 cm extinction cross section per neutral hydrogen atom at the given wavelength and using the default gas properties configured for this material mix. The extinction cross section is identical to the absorption cross section because the scattering cross section is zero.
Implements MaterialMix.
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overridevirtual |
This function returns the 21 scattering cross section per neutral hydrogen atom, which is trivially zero for all wavelengths.
Implements MaterialMix.
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overridevirtual |
This function returns a list of StateVariable objects describing the specific state variables used by the receiving material mix. For this class, the function returns a list containing descriptors for the properties defined in the input model, namely number density and temperature.
Implements MaterialMix.