Star Formation and Feedback Parameters¶

For details on each of the different star formation methods available in Enzo see Active Particles: Stars, BH, and Sinks.

General¶

StarParticleCreation (external)

This parameter is bitwise so that multiple types of star formation routines can be used in a single simulation. For example if methods 1 and 3 are desired, the user would specify 10 (2¹ + 2³), or if methods 1, 4 and 7 are wanted, this would be 146 (2¹ + 2⁴ + 2⁷). Default: 0

- Cen & Ostriker (1992)
- Cen & Ostriker (1992) with stocastic star formation
- Global Schmidt Law / Kravstov et al. (2003)
- Population III stars / Abel, Wise & Bryan (2007)
- Sink particles: Pure sink particle or star particle with wind feedback depending on
     choice for HydroMethod / Wang et al. (2009)
- Radiative star clusters  / Wise & Cen (2009)
- [reserved for future use]
- Cen & Ostriker (1992) with no delay in formation
- Springel & Hernquist (2003)
- Massive Black Hole (MBH) particles insertion by hand / Kim et al. (2010)
- Population III stellar tracers
- Molecular hydrogen regulated star formation

StarParticleFeedback (external)

This parameter works the same way as StarParticleCreation but only is valid for StarParticleCreation method = 0, 1, 2, 7 and 8 because methods 3, 5 and 9 use the radiation transport module and Star_*.C routines to calculate the feedback, 4 has explicit feedback and 10 does not use feedback. Default: 0.

StarFeedbackDistRadius (external)

If this parameter is greater than zero, stellar feedback will be deposited into the host cell and neighboring cells within this radius. This results in feedback being distributed to a cube with a side of StarFeedbackDistRadius+1. It is in units of cell widths of the finest grid which hosts the star particle. Only implemented for StarParticleCreation method = 0 or 1 with StarParticleFeedback method = 1. (If StarParticleFeedback = 0, stellar feedback is only deposited into the cell in which the star particle lives). Default: 0.

StarFeedbackDistCellStep (external)

In essence, this parameter controls the shape of the volume where the feedback is applied, cropping the original cube. This volume that are within StarFeedbackDistCellSteps cells from the host cell, counted in steps in Cartesian directions, are injected with stellar feedback. Its maximum value is StarFeedbackDistRadius * TopGridRank. Only implemented for StarParticleCreation method = 0 or 1 with StarParticleFeedback method = 1. See Distributed Stellar Feedback for an illustration. Default: 0.

StarMakerTypeIaSNe (external)

This parameter turns on thermal and chemical feedback from Type Ia supernovae. The mass loss and luminosity of the supernovae are determined from fits of K. Nagamine. The ejecta are traced in a separate species field, MetalSNIa_Density. The metallicity of star particles that comes from this ejecta is stored in the particle attribute typeia_fraction. Can be used with StarParticleCreation method = 0, 1, 2, 5, 7, and 8. Default: 0.

StarMakerPlanetaryNebulae (external)

This parameter turns on thermal and chemical feedback from planetary nebulae. The mass loss and luminosity are taken from the same fits from K. Nagamine. The chemical feedback injects gas with the same metallicity as the star particle, and the thermal feedback equates to a 10 km/s wind. The ejecta are not stored in its own species field. Can be used with StarParticleCreation method = 0, 1, 2, 5, 7, and 8. Default: 0.

Normal Star Formation¶

The parameters below are considered in StarParticleCreation method 0, 1, 2, 7 and 8.

StarMakerOverDensityThreshold (external): The overdensity threshold in code units (for cosmological simulations, note that code units are relative to the total mean density, not just the dark matter mean density) before star formation will be considered. For StarParticleCreation method = 7 in cosmological simulations, however, StarMakerOverDensityThreshold should be in particles/cc, so it is not the ratio with respect to the DensityUnits (unlike most other star_makers). This way one correctly represents the Jeans collapse and molecular cloud scale physics even in cosmological simulations. Default: 100
StarMakerSHDensityThreshold (external): The critical density of gas used in Springel & Hernquist star formation ( \rho_{th} in the paper) used to determine the star formation timescale in units of g cm^-3. Only valid for StarParticleCreation method = 8. Default: 7e-26.
StarMakerMassEfficiency (external): The fraction of identified baryonic mass in a cell (Mass*dt/t_dyn) that is converted into a star particle. Default: 1
StarMakerMinimumMass (external): The minimum mass of star particle, in solar masses. Note however, the star maker algorithm 2 has a (default off) “stochastic” star formation algorithm that will, in a pseudo-random fashion, allow star formation even for very low star formation rates. It attempts to do so (relatively successfully according to tests) in a fashion that conserves the global average star formation rate. Default: 1e9
StarMakerMinimumDynamicalTime (external): When the star formation rate is computed, the rate is proportional to M_baryon * dt/max(t_dyn, t_max) where t_max is this parameter. This effectively sets a limit on the rate of star formation based on the idea that stars have a non-negligible formation and life-time. The unit is years. Default: 1e6
StarMassEjectionFraction (external): The mass fraction of created stars which is returned to the gas phase. Default: 0.25
StarMetalYield (external): The mass fraction of metals produced by each unit mass of stars created (i.e. it is multiplied by mstar, not ejected). Default: 0.02
StarEnergyToThermalFeedback (external): The fraction of the rest-mass energy of the stars created which is returned to the gas phase as thermal energy. Default: 1e-5
StarEnergyToStellarUV (external): The fraction of the rest-mass energy of the stars created which is returned as UV radiation with a young star spectrum. This is used when calculating the radiation background. Default: 3e-6
StarEnergyToQuasarUV (external): The fraction of the rest-mass energy of the stars created which is returned as UV radiation with a quasar spectrum. This is used when calculating the radiation background. Default: 5e-6

Molecular Hydrogen Regulated Star Formation¶

The parameters below are considered in StarParticleCreation method 11.

H2StarMakerEfficiency (external): See Method 11: Molecular Hydrogen Regulated Star Formation.
H2StarMakerNumberDensityThreshold (external): See Method 11: Molecular Hydrogen Regulated Star Formation.
H2StarMakerMinimumMass (external): See Method 11: Molecular Hydrogen Regulated Star Formation.
H2StarMakerMinimumH2FractionForStarFormation (external): See Method 11: Molecular Hydrogen Regulated Star Formation.
H2StarMakerStochastic (external): See Method 11: Molecular Hydrogen Regulated Star Formation.
H2StarMakerUseSobolevColumn (external): See Method 11: Molecular Hydrogen Regulated Star Formation.
H2StarMakerSigmaOverR (external): See Method 11: Molecular Hydrogen Regulated Star Formation.
H2StarMakerAssumeColdWarmPressureBalance (external): See Method 11: Molecular Hydrogen Regulated Star Formation.
H2StarMakerH2DissociationFlux_MW (external): See Method 11: Molecular Hydrogen Regulated Star Formation.
H2StarMakerH2FloorInColdGas (external): See Method 11: Molecular Hydrogen Regulated Star Formation.
H2StarMakerColdGasTemperature (external): See Method 11: Molecular Hydrogen Regulated Star Formation.
StarFormationOncePerRootGridTimeStep (external): See Method 11: Molecular Hydrogen Regulated Star Formation.

Population III Star Formation¶

The parameters below are considered in StarParticleCreation method 3.

PopIIIStarMass (external): Stellar mass of Population III stars created in StarParticleCreation method 3. Units of solar masses. The luminosities and supernova energies are calculated from Schaerer (2002) and Heger & Woosley (2002), respectively.
PopIIIBlackHoles (external): Set to 1 to create black hole particles that radiate in X-rays for stars that do not go supernova (< 140 solar masses and > 260 solar masses). Default: 0.
PopIIIBHLuminosityEfficiency (external): The radiative efficiency in which the black holes convert accretion to luminosity. Default: 0.1.
PopIIIOverDensityThreshold (external): The overdensity threshold (relative to the total mean density) before Pop III star formation will be considered. Default: 1e6.
PopIIIH2CriticalFraction (external): The H_2 fraction threshold before Pop III star formation will be considered. Default: 5e-4.
PopIIIMetalCriticalFraction (external): The metallicity threshold (relative to gas density, not solar) before Pop III star formation will be considered. Note: this should be changed to be relative to solar! Default: 1e-4.
PopIIISupernovaRadius (external): If the Population III star will go supernova (140<M<260 solar masses), this is the radius of the sphere to inject the supernova thermal energy at the end of the star’s life. Units are in parsecs. Default: 1.
PopIIISupernovaUseColour (external): Set to 1 to trace the metals expelled from supernovae. Default: 0.
PopIIIInitialMassFunction (external): When turned on, each Pop III stellar mass is randomly drawn from an IMF that is Salpeter above some characteristic mass and exponentially cutoff below this mass. Default: 0
PopIIIInitialMassFunctionSeed (external): Random initial seed for the Pop III stellar mass randomizer. Default: INT_UNDEFINED
PopIIILowerMassCutoff (external): Lower limit of the Pop III IMF. Default: 1
PopIIIUpperMassCutoff (external): Upper limit of the Pop III IMF. Default: 300
PopIIIInitialMassFunctionSlope (external): Slope of the Salpeter (high-mass) portion of the Pop III IMF. Default: -1.3
PopIIIInitialMassFunctionCalls (internal): Number of times a Pop III mass has been drawn from the IMF. Used for restarts and reproducibility. Default: 0
PopIIISupernovaMustRefine (external): When turned on, the region around a star about to go supernova is refined to the maximum AMR level. Experimental. Default: 0
PopIIISupernovaMustRefineResolution (external): Used with PopIIISupernovaMustRefine. Minimum number of cells across the blastwave. Default: 32
PopIIIHeliumIonization (external): When turned on, Pop III stars will emit helium singly- and doubly-ionizing radiation. Default: 0
PopIIIColorDensityThreshold (external): Above this density, a Pop III “color” particle forms, and it will populate the surrounding region with a color field. Units: mean density. Default: 1e6
PopIIIColorMass (external): A Pop III “color” particle will populate the surrounding region with a mass of PopIIIColorMass. Units: solar masses. Default: 1e6

Radiative Star Cluster Formation¶

The parameters below are considered in StarParticleCreation method 5.

StarClusterMinDynamicalTime (external): When determining the size of a star forming region, one method is to look for the sphere with an enclosed average density that corresponds to some minimum dynamical time. Observations hint that this value should be a few million years. Units are in years. Default: 1e7.
StarClusterIonizingLuminosity (external): The specific luminosity of the stellar clusters. In units of ionizing photons per solar mass. Default: 1e47.
StarClusterSNEnergy (external): The specific energy injected into the gas from supernovae in the stellar clusters. In units of ergs per solar mass. Default: 6.8e48 (Woosley & Weaver 1986).
StarClusterSNRadius (external): This is the radius of the sphere to inject the supernova thermal energy in stellar clusters. Units are in parsecs. Default: 10.
StarClusterFormEfficiency (external): Fraction of gas in the sphere to transfer from the grid to the star particle. Recall that this sphere has a minimum dynamical time set by StarClusterMinDynamicalTime. Default: 0.1.
StarClusterMinimumMass (external): The minimum mass of a star cluster particle before the formation is considered. Units in solar masses. Default: 1000.
StarClusterCombineRadius (external): It is possible to merge star cluster particles together within this specified radius. Units in parsecs. This is probably not necessary if ray merging is used. Originally this was developed to reduce the amount of ray tracing involved from galaxies with hundreds of these radiating particles. Default: 10.
StarClusterUseMetalField (external): Set to 1 to trace ejecta from supernovae. Default: 0.
StarClusterHeliumIonization (external): When turned on, stellar clusters will emit helium singly- and doubly-ionizing radiation. Default: 0
StarClusterRegionLeftEdge (external): Can restrict the region in which star clusters can form. Origin of this region. Default: 0 0 0
StarClusterRegionRightEdge (external): Can restrict the region in which star clusters can form. Right corner of this region. Default: 1 1 1
StarClusterUnresolvedModel (external): Regular star clusters live for 20 Myr, but this is only valid when molecular clouds are resolved. When this parameter is on, the star formation rate is the same as the Cen & Ostriker exponential rate. Default: 0

Massive Black Hole Particle Formation¶

The parameters below are considered in StarParticleCreation method 9.

MBHInsertLocationFilename (external)

The mass and location of the MBH particle that has to be inserted. For example, the content of the file should be in the following form. For details, see mbh_maker.src. Default: mbh_insert_location.in

#order: MBH mass (in Ms), MBH location[3], MBH creation time
100000.0      0.48530579      0.51455688      0.51467896      0.0

Sink Formation and Feedback¶

The parameters below are considered in sink creation routines: sink_maker, star_maker8, star_maker9 (and occasionally only in certain set-ups). Because many of the following parameters are not actively being tested and maintained, users are encouraged to carefully examine the code before using it.

AccretionKernal (external): While this parameter is used to determine the accretion kernel in star_maker8.C, there is no choice other than 1 at the moment: Ruffert, ApJ (1994) 427 342 (a typo in the parameter name...). Default: 0
StellarWindFeedback (external): This parameter is used to turn on sink particle creation by star_maker8.C and also its feedback. Currently implemented are: 1 - protostellar jets along the magnetic fields, 2 - protostellar jets along random directions, 3 - isotropic main sequence stellar wind, 4 - not implemented, 5 - not implemented, 6 - methods 2 and 3 combined. Default: 0
StellarWindTurnOnMass (external): This parameter is used to decide whether mass increase reached the ejection threshold for StellarWindFeedback=1, 2, or 6 in star_maker8.C. Default: 0.1
MSStellarWindTurnOnMass (external): This parameter is used to decide whether mass increase reached the ejection threshold for StellarWindFeedback = 3 or 6 in star_maker8.C. Default: 10.0
BigStarFormation (external): This parameter is used to turn on sink particle creation by star_maker9.C.
BigStarFormationDone (external): In star_maker9.C, this parameter is used when we do not want to form BigStars any more.
BigStarSeparation (external): In star_maker[89].C, if the newly-created sink particle is within a certain distance from the closest pre-existing sink, then add to it rather than creating a new one.
SinkMergeDistance: [not used]
SinkMergeMass: [not used]

Enzo 2.2 documentation