delta_vir¶
- halotools.empirical_models.delta_vir(cosmology, redshift)[source]¶
The virial overdensity in units of the critical density, using the fitting formula of Bryan & Norman 1998, assuming \(\Omega_{\Lambda} = 0.\)
\(\Delta_{\rm vir}(x) = 18\pi^{2} + 82x - 39x^{2}\), where \(x \equiv \Omega_{m}(z)-1\).
See Halo Mass and Radius Definitions for details.
- Parameters:
- cosmologyobject
Instance of an Astropy
cosmology
object.- redshift: array_like
Can be a scalar or a numpy array.
- Returns:
- delta: array_like
The virial overdensity. Has the same dimensions as the input
redshift
.
See also
density_threshold
The threshold density for a given mass definition.