Individual Star Formation and Feedback: Parameters


The tables below list all parameters relevant to the formation and feedback associated with our individual star methods. Included at the very bottom are input parameters to set specific to chemical evolution and certain problem types, related to these methods.

Star Formation and Supernova Feedback

Enzo Name Description Value(s) Notes Refs.
IndividualStarIMFUpperMassCutoff Upper limit of IMF 100.0 M\(_{\odot}\)
IndividualStarIMFLowerMassCutoff Lower limit of IMF 1.0 M\(_{\odot}\)
IndividualStarVelocityDispersion At formation, stars are given random velocity from Guassian distribution with mean velocity determined by the local gas velocity and dispersion set by this parmeter 1.0 km s\(^{-1}\) T.B.D, but 1.0 km s\(^{-1}\) is reasonable
IndividualStarIMFSeed random number seed (arbitrary)
0 = Salpeter
IndividualStarIMF 1 = Kroupa 0
2 = Chabrier
IndividualStarIMFCalls Number of calls to IMF to reset rnum generator on restart Not to be set by user, but saved at each dump file
IndividualStarSalpeterSlope \(\alpha\) for Salpeter 2.35
IndividualStarKroupaAlpha1 \(\alpha\) for first mass bin 1.3
IndividualStarKroupaAlpha2 \(\alpha\) for second mass bin 1.3
IndividualStarKroupaAlpha3 \(\alpha\) for third mass bin 2.3
IndividualStarMassFraction Maximum fraction, \(f_{\rm gas \to *}\), of baryon mass in cell that can be converted to stars in a single timestep. If \(M_{\rm IMF,min} < f_{\rm gas \to *} M_{\rm gas} < M_{\rm IMF,max}\), then IMF is truncated for that cell such that \(M_{\rm IMF,max} = f_{\rm gas \to *} M_{\rm gas}\) 0.5 Proper value requires testing and discussion From method used in Goldbaum et. al. 2015
IndividualStarSNIIMassCutoff Stellar mass above which star produces CC SN 8.0 M\(_{\odot}\) T.B.D
IndividualStarWDMinimumMass Lower mass limit for stars that turn into WD 1.7 M\(_{\odot}\) 1.7 M\(_{\odot}\) is lower limit of empirical intiial to final mass relation used to set WD masses Salaris et. al. 2009 for DTD
IndividualStarWDMaximumMass Upper mass limit for stars to turn into WD 8.0 M\(_{\odot}\) Dahlen et. al. 2004, Mannuci et. al. 2006, Maoz & Mannucci 2012
IndividualStarUseSNIa Switch to enable SN Ia and turn on / of WD formation 0 or 1 Default ON
IndividualStarSNIaMinimumMass Lower mass limit of a WD’s progenitor star that is capable of going SN Ia 3 M\(_{\odot}\) Not well understood value, but default is what is typically assumed
IndividualStarSNIaMaximumMass Maximum mass limit “ ” 8.0 M\(_{\odot}\) “”
IndividualStarSNIaFraction Normalizes probability distribution for SNIa rates, and is the fraction of stars in the above mass range that will explode as SN Ia given a Hubble time 0.043 Fraction is on order of a few percent, but depends on choice of IMF and normalization of the delay time distribution (DTD)
IndividualStarDTDSlope \(\beta\) in power law decay (\(t^{-\beta}\)) of DTD that sets the decay of probabilty as a function of time for our WD’s to explode as SNIa 1.07 Mean from Cote et. al. 2015. Values vary, but around 1.0-1.3 Maoz et. al. 2012 , Maoz et. al. 2014 and Cote et. al. 2015 for compilation
IndividualStarStellarWinds Turn stellar winds on or off 1 Winds not yet coded
IndividualStarRadiationMinimumMass Stars above this value are radiation sources if radiation is ON 8.0 M\(_{\odot}\) Used value is T.B.D.
IndividualStarBlackBodyOnly Radiation is (by default) calulated using OSTAR2002 grid for stars with \(T_{\rm eff}\) and \(g\) on the grid. When off the grid, a black body curve is used. This turns off OSTAR2002 for all stars if ON 0 0 or 1
IndividualStarFollowStellarYields If ON, and MultiMetals enabled, this tags stars with chemical abundances of their formation cells AND enables chemical ejection during feedback modes 1 Feedback of metals not in place
IndividualStarWindTemperature Temperature ceiling for injection region in stellar wind model. Exceeding this temperature engages wind mass loading 1.0E6 A few million is ideal Weaver 1977, Koo & McKee 1992 a,b
IndivudalStarUseWindMixingModel On or Off - If on, mass loads winds with grid averaged metal abundances in order to maintain IndividualStarWindTemperature winds 1 Strong recommendation to leave on
IndividualStarFeedbackOverlapSample Number of sampling points per cell in volume overlap calculation 20 10-20 seems to produce reasonable spherical winds with few zone radius injection regions - much higher is expensive

Cosmic Rays

Cosmic rays are controlled by the adopted diffusion coefficient, the adiabatic index, maximum sound speed, and fraction of SN energy deposited into cosmic rays (and subtracted from the total thermal energy input). There will be an initial cosmic ray energy density that we need to decide what to do with... possibly we should just set it to be dynamically insigificant initially....

Enzo Name Description Value(s) Notes Refs.
CRModel CR’s on or off 1 likely test on and off
CRDiffusion Diffusion on or off 1 test on and off
CRkappa Cosmic ray diffusion coefficent ?? This will require testing and conversation
CRFeedback Fraction of SN energy converted into CR’s rather than thermal 0.25 Again, testing needed
GalaxySimulationCR Sets initial CR energy density as fraction of thermal energy ??


Below are new radiation parameters:

Enzo Name Description Value(s) Notes REfs.
self_shielding_method Switch between self shielding approximations in GRACKLE 0 = no shielding, 1 = e\(^{-\tau}\), 2 = Rahmati et. al. 2013 in HI, e\(^{-\tau}\) in HeI and HeII , 3 = Rahmati et. al. 2013 in HI and HeI, none in HeII Rahmati et. al. 2013
IndividualStarBlackBodyq0Factors Fit factors to smooth HI ionzing radiation 0.1, 3.2
IndividualStarBlackBodyq1Factors 0.001, 4.0
IndividualStarBlackBodyFUVFactors 10\(^{-4}\), 2.3\(\times 10^{-5}\)
IndividualStarBlackBodyLWFactors 5.0\(\times 10^{-5}\), 5.0\(\times 10^{-6}\)

The radiation parameters specific to my stars are discussed above (i.e. how the ionizing rate is calculated for each star). These are the radiative transfer parameters relevant to our simulation.

Enzo Name Description Value(s) Notes Refs.
RadiativeTransfer On or Off On Test both
RadiativeTransferRadiationPressure Compute radiation pressure. Currently ONLY handles pressure felt by hydrogen (on or off) 1
RadiativeTransferRaysPerCell Number of photon rays computed in each cell (effectively a photon resolution) 5 may need to play with this, 5 is default
RadiativeTransferSourceRadius Radiation sources are considered point sources, but will radiate as uniform sphere of desired value if > 0 0 I don’t think we need this, and i think it fixes the radius to a single value, not a value per star. But if we have R for each star anyway, this might be useful? Not sure if its relevant
RadiativeTransferPropogationSpeedFraction Photon speed as fraction of c 1 Lower number is less accurate but computationally easier, ideally stick with 1

Multi species and Chemistry

General parameters for turning multispecies and chemistry on / off for our simulations. The chemistry parameters (multi metals) are new.

ProblemType 260: ChemicalEvolutionTest

A new problem type was created that was meant to be used to test the physics associated with both the individual star formation / feedback as well as the chemical evolution. This initializes a star at the center of a uniform box of gas and lets it evolve. If one is impatient, one can manually set the star lifetime to an arbitrarily small value if one is concerned only with end-of-life (i.e. supernova) effects.

This star is deposited within the first timestep, and is not present at t = 0. Star formation is turned off for the remainder of the simulation.

Enzo Name Description Value(s) Notes Refs.
ChemicalEvolutionTestStarMass Mass of star (arbitrary)
ChemicalEvolutionTestStarMetallicity Metal fraction of star (arbitrary)
ChemicalEvolutionTestStarLifetime Manually set star lifetime 0 Value of 0 turns this off and lifetime is calculated as normal from stellar properties. > 0 is lifetime in Myr
ChemmicalEvolutionTestStarPosition Coordinates of position in code units 0.5 0.5 0.5 center

ProblemType 31: GalaxySimulation

A few parameters were added to the galaxy simulation problem type to set initial values for disk / halo chemical properties. A few of these new parameters below are stored in the TestProblemData struct that can be used in most simulations (see the next section) TestProblemData is used to set initial metal fractions for all species, and is coded to set two values per species for use with two different regimes in a given initial conditions set up. This is simple, but coding this for arbitrary locations is not trivial. For reading GalaxySimulation code, any TestProblemData with XX is used to set the disk initial values, and any with XX is used to set the halo / ambient medium initial values. If nothing is specified, the default is to set everything as primordial with the various metal fractions set to “tiny_number”.

I’ve also added a bunch of parameters to set MultiSpecies initial conditions following IC’s in other problem types for doing so.

Enzo Name Description Value(s) Notes Refs.
TestProblemUseMetallicityField Enables metallicity tracking 1 This is unfortunate, but there is a GalaxySimulationUseMetallicityField parameter that already exists, but DOES NOT actually enable metallicity fraction tracking, but a different tracer field (disk, not disk). I made this parameter as to not break previous functionality, but naming is unfortunate