delta_vir¶

halotools.empirical_models.delta_vir(cosmology, redshift)[source] [edit on github]

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: cosmology : object Instance of an Astropy cosmology object. redshift: array_like Can be a scalar or a numpy array. delta: array_like The virial overdensity. Has the same dimensions as the input redshift.

density_threshold