SAGE26 Parameter Reference

This document is the canonical reference for every parameter accepted by SAGE26 parameter files (input/*.par). Parameter files are parsed by src/core_read_parameter_file.c.

Syntax: ParameterName  value  % optional comment

Lines beginning with % are comments. Required parameters must be present; optional parameters take the listed default if omitted.

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Output

Parameter	Type	Required	Default	Description
FileNameGalaxies	string	yes	—	Base name for output files (e.g. model → model_0.hdf5).
OutputDir	string	yes	—	Directory for galaxy output. Created if absent.
OutputFormat	string	no	sage_hdf5	sage_hdf5 or sage_binary.
NumOutputs	int	no	-1	Number of snapshot outputs; -1 = all snapshots.
SaveFullSFH	0/1	no	1	Store per-snapshot SFR history arrays (SFHMassDisk, SFHMassBulge).
TrackICSAssembly	0/1	no	1	Record satellite disruption contributions to ICS (ICS_disrupt, ICS_accrete).

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Simulation

Parameter	Type	Required	Default	Description
TreeType	string	yes	—	Merger tree format: lhalo_binary, lhalo_hdf5, consistent_trees_ascii, consistent_trees_hdf5, genesis_lhalo_hdf5, gadget4_hdf5.
TreeName	string	yes	—	Tree file basename (files are named TreeName.N).
SimulationDir	string	yes	—	Directory containing tree files.
FileWithSnapList	string	yes	—	File listing snapshot scale factors, one per line.
FirstFile	int	yes	—	First tree file index to process.
LastFile	int	yes	—	Last tree file index to process (inclusive).
NumSimulationTreeFiles	int	yes	—	Total number of tree files (may differ from FirstFile–LastFile range).
LastSnapshotNr	int	yes	—	Index of the final snapshot in the tree files.
Omega	double	yes	—	Matter density parameter Ω_m.
OmegaLambda	double	yes	—	Dark energy density parameter Ω_Λ.
BaryonFrac	double	yes	—	Universal baryon fraction f_b = Ω_b / Ω_m.
Hubble_h	double	yes	—	Dimensionless Hubble parameter h (H₀ = 100 h km/s/Mpc).
PartMass	double	yes	—	N-body particle mass in 10¹⁰ M_sun/h.
BoxSize	double	yes	—	Simulation box side length in Mpc/h.

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Units

Parameter	Type	Required	Default	Description
UnitLength_in_cm	double	yes	—	1 internal length unit in cm. Typically 3.08568e+24 (= Mpc/h).
UnitMass_in_g	double	yes	—	1 internal mass unit in g. Typically 1.989e+43 (= 10¹⁰ M_sun).
UnitVelocity_in_cm_per_s	double	yes	—	1 internal velocity unit in cm/s. Typically 100000 (= km/s).

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Physics switches

Parameter	Type	No	Default	Values and meaning
SFprescription	int	no	1	Star formation prescription: 0=Croton+06; 1=Blitz & Rosolowsky 06 H₂; 2=Somerville+25 SFR; 3=Somerville+25 SFR+H₂; 4=Krumholz & Dekel 12; 5=KMT 09; 6=Krumholz 13; 7=Gnedin & Draine 14.
AGNrecipeOn	int	no	2	AGN feedback: 0=off; 1=empirical; 2=Bondi-Hoyle; 3=cold cloud accretion.
SupernovaRecipeOn	0/1	no	1	SN feedback: 0=off; 1=Croton+16 reheating/ejection.
ReionizationOn	0/1	no	1	Reionization suppression of infall: 0=off; 1=Kravtsov+04 analytic fit.
DiskInstabilityOn	0/1	no	1	Disk instability: 0=off; 1=Toomre criterion drives bulge and BH growth.
CGMrecipeOn	0/1	no	1	Two-regime CGM model: 0=off (classical C16 cooling only); 1=on.
FIREmodeOn	0/1	no	1	FIRE stellar feedback: 0=off; 1=on.
FeedbackFreeModeOn	int	no	1	Feedback-free burst galaxies: 0=off; 1=Li+24 sigmoid; 2=BK25 (Ishiyama+21 c); 3=BK25 (ConcentrationOn method); 4=BK25 + log-normal c scatter; 5=Li+24 sharp; 6=Li+24 sigmoid + H₂ SF; 7=BK25 log-normal c scatter + H₂ SF.
ConcentrationOn	int	no	3	Halo concentration method: 0=off; 1=Ishiyama+21 table; 2=V_max/V_vir; 3=V_max/V_vir with infall freeze for satellites.
BulgeSizeOn	int	no	3	Bulge radius model: 0=off; 1=Shen+2003 eq.33; 2=Shen+2003 eq.32; 3=Tonini+2016 (separate merger and instability channels, mass-weighted average).
StarburstColdGasOn	0/1	no	1	Include cold gas contribution during merger starbursts.
DynamicDisruptionSplit	int	no	2	ICS-vs-BCG split for disrupted satellite stellar mass: 0=fixed fraction FractionDisruptedToICS; 1=mass-ratio split f_ICS = 1 - (infallMvir / Mhost)^DisruptionSplitAlpha; 2=mass-ratio split with concentration weighting (alpha_eff = DisruptionSplitAlpha * DisruptionSplitCref / c_sat).

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CGM model parameters

Parameter	Type	Required	Default	Description
CGMDensityProfile	int	no	0	CGM gas density profile for precipitation: 0=uniform; 1=NFW; 2=beta (β=2/3).
CGMAGNOn	0/1	no	1	Enable AGN heating coupling to the CGM-regime cooling path.

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FFB parameters

Parameter	Type	Required	Default	Description
FFBMaxEfficiency	double	no	0.2	Maximum star formation efficiency during FFB bursts. 0.2 matches observations; 1.0 is the theoretical maximum.
FFBConcSigma	double	no	0.2	Log-normal scatter in halo concentration used by FeedbackFreeModeOn=4,7 (dex).
FFBIgnoreRegime	0/1	no	1	Apply FFB criterion regardless of CGM regime classification.
FFBRandomMode	0/1	no	0	Use random number scatter in FFB threshold instead of deterministic sigmoid.
RedshiftPowerLawExponent	double	no	1.25	Redshift exponent in the FFB mass threshold scaling (Li+24 eq. 2).

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H₂ star formation parameters

Parameter	Type	Required	Default	Description
H2DiskAreaOption	int	no	1	Disk area for H₂ surface density: 1=π r_disk²; 2=π (3 r_disk)²; 3=2π r_disk².
H2RadialIntegrationOn	0/1	no	1	Use radial ring integration for H₂ fraction (more accurate, slower).
H2RadialNBins	int	no	25	Number of radial bins for the ring integration.
H2RadialRMaxFactor	double	no	5.0	Outer integration radius as a multiple of the disk scale radius.

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Model parameters

Star formation

Parameter	Units	Default	Description
SfrEfficiency	dimensionless	0.05	Cold/H2 gas consumption efficiency per dynamical time. Used by SFprescription 0, 1, 4, 5, 7 unconditionally, and by 6 (K13) only in the single-slab path (H2RadialIntegrationOn=0). Unused by 2 and 3 (Somerville+25 use their own density-modulated epsilon_cl) and by 6 in the radial path (uses the K13 local depletion time natively).
RecycleFraction	dimensionless	0.43	Fraction of stellar mass instantaneously recycled to cold gas.
Yield	dimensionless	0.025	Fraction of stellar mass returned as metals.
FracZleaveDisk	dimensionless	0.0	Fraction of newly produced metals transferred directly to hot gas.

Supernova feedback

Parameter	Units	Default	Description
FeedbackReheatingEpsilon	dimensionless	2.9	Mass of cold gas reheated per unit of stellar mass formed (Martin 1999).
FeedbackEjectionEfficiency	dimensionless	0.3	Fraction of SN energy deposited into hot gas for ejection.
EnergySN	erg	1.0e51	Energy per supernova event.
EtaSN	M_sun⁻¹	5.0e-3	Number of supernovae per solar mass of stars formed.

AGN feedback

Parameter	Units	Default	Description
RadioModeEfficiency	dimensionless	0.08	AGN radio-mode heating efficiency (AGNrecipeOn=2).
QuasarModeEfficiency	dimensionless	0.005	AGN quasar-mode wind heating efficiency (AGNrecipeOn > 0).
BlackHoleGrowthRate	dimensionless	0.015	Fraction of cold gas accreted onto the BH during mergers (AGNrecipeOn > 0).

Mergers

Parameter	Units	Default	Description
ThreshMajorMerger	dimensionless	0.3	Mass ratio above which a merger is classified as major.
ThresholdSatDisruption	dimensionless	1.0	M_vir-to-baryonic mass ratio below which a satellite is disrupted rather than merged.
FractionDisruptedToICS	dimensionless	0.8	Fixed fraction of disrupted satellite stellar mass that goes to ICS (vs. central BCG). Used when DynamicDisruptionSplit=0, and as the fallback when modes 1/2 cannot compute a mass ratio.
DisruptionSplitAlpha	dimensionless	0.25	Power-law exponent for the mass-dependent disruption split.
DisruptionSplitCref	dimensionless	10.0	Reference concentration for the disruption split.

Gas cycling

Parameter	Units	Default	Description
ReIncorporationFactor	dimensionless	0.15	Fraction of ejected mass reincorporated per dynamical time.

Reionization

Parameter	—	Default	Description
Reionization_z0	—	8.0	Characteristic redshift for reionization suppression (Kravtsov+04).
Reionization_zr	—	7.0	Width parameter for reionization suppression.

See the FFB parameters section above for FFBMaxEfficiency, FFBConcSigma, and RedshiftPowerLawExponent.

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MPI forest distribution

Parameter	Type	Required	Default	Description
ForestDistributionScheme	string	no	generic_power_in_nhalos	How forests are distributed over MPI tasks: uniform_in_forests, linear_in_nhalos, quadratic_in_nhalos, exponent_in_nhalos, generic_power_in_nhalos.
ExponentForestDistributionScheme	double	no	0.7	Exponent for exponent_in_nhalos or generic_power_in_nhalos schemes.