Merger Tree Building Mass Resolutions

Class providing the minimum progenitor halo mass (mass resolution) to resolve when building a merger tree. Branches below this mass are not followed individually; instead their accreted mass is treated as smooth, unresolved accretion onto the main progenitor. The mass resolution controls the trade-off between completeness of the merger history and computational cost, and can be set as a fixed value, a fraction of the root halo mass, or adaptively based on tree size.

Default implementation: mergerTreeMassResolutionFixed

Methods

resolution → double precision

Gives the mass resolution to use for the given tree.

  • type(mergerTree), intent(in ) :: tree

mergerTreeMassResolutionFixed

A merger tree mass resolution class which assumes a fixed, uniform mass resolution applied to all merger trees during tree construction. The minimum resolved halo mass is set by the [massResolution] parameter, expressed in Solar masses, below which branches are not built.

(Default implementation)

Parameters

  • [mass] (default 100.0d0) — The fixed mass (in \(\mathrm{M}_\odot\)) assigned to all newly-formed seed black holes in this implementation, representing the initial black hole mass when a halo first forms a central black hole.

  • [spin] (default 0.0d0) — The dimensionless spin parameter (between \(-1\) and \(+1\)) assigned to all newly-formed seed black holes, where \(0\) corresponds to a non-rotating Schwarzschild black hole and \(\pm 1\) to a maximally rotating Kerr black hole.

  • [fraction] (default 0.01d0) — The fixed fraction \(f_\mathrm{outflow}\) of the stellar energy input rate (normalized to a canonical \(1\,\mathrm{M}_\odot\) population) that drives gas outflows, setting the mass loading factor for stellar feedback in the galaxy.

  • [escapeFraction] (default 0.006d0) — Escape fraction of ionizing photons from young HII regions.

  • [ageLimit] (default 0.03d0) — The age beyond which all ionizing photons are assumed to escape from HII regions.

  • [timescale] (default 1.0d0) — The timescale for star formation in the fixed timescale model.

  • [rateStarFormation] (default 1.0d9) — The rate of star formation in units of \(\mathrm{M}_\odot \hbox{Gyr}^{-1}\).

  • [proposalSize] — The fixed value of the proposal scaling parameter \(\gamma\) used to scale the vector difference between two randomly selected chain states when forming differential evolution proposals.

  • [exponentValue] — The fixed value of the temperature-scaling exponent \(\alpha\) by which the proposal size \(\gamma\) is scaled as \(\gamma \propto T^{\alpha}\) in tempered differential evolution runs.

  • [massResolution] (default 5.0d9) — The mass resolution to use when building merger trees.

  • [rootVariance] — The root variance of the random error distribution.

  • [velocityRadial] (default -0.90d0) — The radial velocity (in units of the host virial velocity) to used for the fixed virial orbits distribution. Default value matches approximate peak in the distribution of Benson (2005).

  • [velocityTangential] (default 0.75d0) — The tangential velocity (in units of the host virial velocity) to used for the fixed virial orbits distribution. Default value matches approximate peak in the distribution of Benson (2005).

  • [rateCoefficient] — The rate coefficient (in units of cm\(^3\) s\(^{-1}\)) for radiative recombination.

  • [gamma] (default 0.67d0) — The multiplicative factor, \(\gamma\), used to compute the cooling coefficient.

  • [fractionLossAngularMomentum] (default 0.3d0) — Specifies the fraction of angular momentum that is lost from cooling/infalling gas.

  • [concentration] — The fixed NFW concentration parameter \(c = r_\mathrm{virial}/r_\mathrm{scale}\) assigned to all halos regardless of mass or redshift, representing the ratio of the virial radius to the scale radius of the dark matter density profile.

  • [metallicity] — The metallicity (relative to Solar) of the IGM.

  • [factor] (default sqrt(0.5d0)) — The ratio of galaxy radius to \(\lambda r_\mathrm{vir}\) in the “fixed” galactic structure radius solver algorithm. This will be applied to any component for which no component-specific value is provided.

  • [factorDisk] (default sqrt(0.5d0)) — The ratio of galaxy radius to \(\lambda r_\mathrm{vir}\) in the “fixed” galactic structure radius solver algorithm for disks. This will override the generic value supplied by [factor] for disks.

  • [factorSpheroid] (default sqrt(0.5d0)) — The ratio of galaxy radius to \(\lambda r_\mathrm{vir}\) in the “fixed” galactic structure radius solver algorithm for spheroids. This will override the generic value supplied by [factor] for spheroids.

  • [radiusFixed] (default var_str('virial')) — The radius to use in the “fixed” galactic structure radius solver algorithm. Allowed options are “virial” and “turnaround”.

  • [overdensity] — The fixed linear overdensity \(\delta\) of the large-scale environment assigned uniformly to all halos; a positive value places halos in an overdense region, while negative values simulate voids.

  • [radiusEnvironment] (default 0.0d0) — The radius of the sphere used to determine the variance in the environmental density.

  • [massEnvironment] (default 1.0d15) — The mass within the sphere sphere used to determine the variance in the environmental density.

  • [densityContrastValue] (default 200.0d0) — The virial density contrast to use in the fixed value model.

  • [densityType] (default var_str('critical')) — The reference density to use in the fixed value virial density contrast model. Either of critical and mean are allowed.

  • [turnAroundOverVirialRadius] (default 2.0d0) — The ratio of the turnaround to virial radii in the fixed value model.

  • [criticalOverdensity] (default (3.0d0/20.0d0)*(12.0d0*Pi)**(2.0d0/3.0d0)) — The value to use for the critical overdensity for collapse of dark matter halos when using a fixed value.

mergerTreeMassResolutionScaled

A merger tree mass resolution class which computes the mass resolution to be min([massResolutionMaximum],max([massResolutionMinimum],[massResolutionFractional]\(\times M_\mathrm{base}\))), where \(M_\mathrm{base}\) is the base mass of the merger tree.

Parameters

  • [massResolutionMinimum] (default 5.0d9) — The minimum mass resolution to use when building merger trees.

  • [massResolutionMaximum] (default huge(0.0d0)) — The maximum mass resolution to use when building merger trees.

  • [massResolutionFractional] (default 1.0d-3) — The fraction of the tree’s root node mass to be used for the mass resolution when building merger trees.

  • [scale] (default 1.0d0) — The multiplicative factor applied to the rms mass variance \(\sigma(M,t)\) returned by the wrapped cosmologicalMassVarianceClass object, allowing renormalization of the power spectrum amplitude.