Star Formation Timescales

Class providing models of the timescale (in Gyr) over which gas is converted into stars in a galaxy component. The star formation timescale sets the depletion time of the gas reservoir—the ratio of available gas mass to star formation rate—and is a key regulator of galaxy growth. Implementations may tie the timescale to the local dynamical time, gas surface density, or molecular gas fraction, with different dependencies expected for disk versus spheroid components.

Default implementation: starFormationTimescaleDynamicalTime

Methods

timescale → double precision

Returns the timescale (in Gyr) for star formation in the provided component.

  • class(nodeComponent), intent(inout) :: component

starFormationTimescaleBaugh2005

A star formation timescale class which adopts the star formation rate given by a modified version of the Baugh et al. (2005) prescription:

\[\tau_\star = \tau_0 (V_\mathrm{disk}/V_0)^\alpha a^\beta\]

where \(\tau_0=\)[timescale], \(\alpha=\)[exponentVelocity], \(\beta=\)[exponentExpansionFactor], and \(V_0=\)[velocityNormalization].

Parameters

  • [timescale] (real; default 8.0d0) — The timescale (in Gyr) for star formation in the Baugh et al. (2005) prescription.

  • [exponentVelocity] (real; default -3.0d0) — The exponent for velocity in the Baugh et al. (2005) prescription for star formation.

  • [exponentExpansionFactor] (real; default 0.0d0) — The exponent for expansion factor in the Baugh et al. (2005) prescription for star formation.

  • [velocityNormalization] (real; default 200.0d0) — The normalization velocity \(V_0\) (in km/s) appearing in the Baugh et al. (2005) star formation timescale relation \(\tau_\star = \tau_0 (V_\mathrm{disk}/V_0)^\alpha a^\beta\).

starFormationTimescaleDynamicalTime

A star formation timescale class in which the star formation timescale scales with the component dynamical time. Specifically:

\[\tau_\star = \epsilon_\star^{-1} \tau_\mathrm{dynamical} \left( {V \over 200\hbox{km/s}} \right)^{\alpha_\star},\]

where \(\epsilon_\star=\)[efficiency] and \(\alpha_\star=\)[exponentVelocity] are input parameters, \(\tau_\mathrm{dynamical}\equiv r/V\) is the dynamical timescale of the component and \(r\) and \(V\) are the characteristic radius and velocity respectively of the component. The timescale is not allowed to fall below a minimum value specified by [timescaleMinimum] (in Gyr).

(Default implementation)

Parameters

  • [efficiency] (real; default 0.01d0) — The efficiency of star formation for the dynamical time method.

  • [exponentVelocity] (real; default -1.50d0) — The velocity exponent for star formation for the dynamical time method.

  • [timescaleMinimum] (real; default 1.0d-3) — The minimum allowed timescale for star formation (in Gyr) in the dynamical time prescription, preventing unphysically short formation timescales in high-density or high-velocity systems.

starFormationTimescaleFixed

A star formation timescale class that returns a constant, user-specified gas consumption timescale regardless of the galactic component properties. This implements the simplest possible star formation model for testing and comparison purposes. The timescale is set by the [timescale] parameter in units of Gyr.

Parameters

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

starFormationTimescaleHaloScaling

A star formation timescale class in which the timescale scales with halo properties. Specifically,

\[\tau_\star = \tau_\mathrm{\star,0} \left( {V_\mathrm{vir} \over 200\hbox{km/s}} \right)^{\alpha_\star} (1+z)^{\beta_\star},\]

where \(\tau_\mathrm{\star,0}=\)[timescale], \(\alpha_\star=\)[exponentVelocityVirial], and \(\beta_\star=\)[exponentRedshift].

Methods

  • calculationReset — Reset memoized calculations.

Parameters

  • [timescale] (real; default 1.0d0) — The timescale for star formation in the halo scaling timescale model.

  • [exponentVelocityVirial] (real; default 0.0d0) — The exponent of virial velocity in the timescale for star formation in the halo scaling timescale model.

  • [exponentRedshift] (real; default 0.0d0) — The exponent of redshift in the timescale for star formation in the halo scaling timescale model.

starFormationTimescaleLowerLimited

A timescale for star formation which limits the timescale to be above a given multiple of the component dynamical time.

Parameters

  • [timescaleMinimum] (real; default 1.0d-3) — The minimum timescale for star formation in units of the dynamical time.

starFormationTimescaleVelocityMaxScaling

A star formation timescale class that scales the gas consumption timescale as a power law in the host halo maximum circular velocity and redshift. The normalization is set by [timescale], and the power-law exponents with respect to velocity and \((1+z)\) are set by [exponentVelocity] and [exponentRedshift] respectively.

Methods

  • calculationReset — Reset memoized calculations.

Parameters

  • [timescale] (real; default 1.0d0) — The timescale (in Gyr) for cooling in low mass halos at \(z=0\) in the velocity maximum scaling scaling cooling rate model.

  • [exponentVelocity] (real; default 0.0d0) — The exponent of velocity in the cooling timescale for low mass halos in the velocity maximum scaling scaling cooling rate model.

  • [exponentRedshift] (real; default 0.0d0) — The exponent of \((1+z)\) in the cooling timescale for low mass halos in the velocity maximum scaling scaling cooling rate model.