Population Parameters

Most often what we’re interested in is producing a model for the ionization and/or thermal history of the Universe, which requires a model

Basic Properties

formation_epoch

Redshift interval over which sources are “on.”

Default: (50, 0)

is_lya_src

Sources contribute to Ly-\(\alpha\) background?

Default: True

is_ion_src_cgm

Sources contribute to growth of HII regions?

Default: True

is_ion_src_igm

Sources contribute ionization in bulk IGM?

If approx_xrb=True, this ionization rate assumes a mean X-ray photon energy of xray_Eavg, which is 500 eV by default.

Default: True

is_heat_src_igm

Sources emit X-rays and heat bulk IGM?

Default: True

Star formation history

Tmin

Minimum virial temperature of star-forming halos.

Default: \(10^4\) [Kelvin]

Mmin

Minimum mass of star-forming halos. Will override Tmin if set to something other than None.

Default: None [\(M_{\odot}\)]

fstar

Star formation efficiency, \(f_{\ast}\), i.e., fraction of collapsing gas that turns into stars.

Default: 0.1

Note

If you set fstar to None, the strength of radiation backgrounds will be determined by the \(\xi\) parameters, xi_LW, xi_XR, and xi_UV.

sfrd

The star formation rate density (SFRD) as a function of redshift. If provided, will override Tmin and Mmin. For example, a constant (co-moving) SFRD of \(1 \ M_{\odot} \ \text{yr}^{-1} \ \text{cMpc}^{-3}\) would be sfrd=lambda z: 1.0.

Default: None [\(M_{\odot} \ \text{yr}^{-1} \ \text{cMpc}^{-3}\)]

X-ray background

cX

Normalization of the X-ray luminosity to star formation rate (\(L_X\)-SFR) relation in band given by spectrum_EminNorm and spectrum_EmaxNorm. If approx_xrb=1, this represents the X-ray luminosity density per unit star formation, such that the heating rate density will be equal to \(\epsilon_X = f_{X,h} c_X f_X \times \text{SFR}\).

Default: \(3.4 \times 10^{40}\) [\(\text{erg} \ \text{s}^{-1} \ (M_{\odot} \ \mathrm{yr}^{-1})^{-1}\)]

fX

Constant multiplicative factor applied to cX, which is typically chosen to match observations of nearby star-forming galaxies, i.e., fX parameterizes ignorance in redshift evolution of cX.

Default: 0.2

Radiation at energies below the Lyman Limit

Nlw

Number of photons emitted in the Lyman-Werner band per baryon of star formation.

If fstar is not None, the co-moving LW luminosity density is given by \(f_{\ast} N_{\mathrm{LW}} \text{SFRD}\).

Default: 9690

xi_LW

Alternative to using Nlw – which is multiplied by the SFRD and thus fstar – which

Ultraviolet emission

Nion

Number of ionizing photons emitted per baryon of star formation.

Default: 4000

fesc

Escape fraction of ionizing radiation.

Default: 0.1