Source code for lenstronomy.Cosmo.background
from __future__ import print_function, division, absolute_import, unicode_literals
__author__ = 'sibirrer'
import numpy as np
import lenstronomy.Util.constants as const
from lenstronomy.Cosmo.cosmo_interp import CosmoInterp
__all__ = ['Background']
[docs]class Background(object):
"""
class to compute cosmological distances
"""
def __init__(self, cosmo=None, interp=False, **kwargs_interp):
"""
:param cosmo: instance of astropy.cosmology
:param interp: boolean, if True, uses interpolated cosmology to evaluate specific redshifts
:param kwargs_interp: keyword arguments of CosmoInterp specifying the interpolation interval and maximum
redshift
:return: Background class with instance of astropy.cosmology
"""
if cosmo is None:
from astropy.cosmology import default_cosmology
cosmo = default_cosmology.get()
if interp:
self.cosmo = CosmoInterp(cosmo, **kwargs_interp)
else:
self.cosmo = cosmo
[docs] def a_z(self, z):
"""
returns scale factor (a_0 = 1) for given redshift
:param z: redshift
:return: scale factor
"""
return 1./(1+z)
[docs] def d_xy(self, z_observer, z_source):
"""
:param z_observer: observer redshift
:param z_source: source redshift
:return: angular diameter distance in units of Mpc
"""
D_xy = self.cosmo.angular_diameter_distance_z1z2(z_observer, z_source)
return D_xy.value
[docs] def ddt(self, z_lens, z_source):
"""
time-delay distance
:param z_lens: redshift of lens
:param z_source: redshift of source
:return: time-delay distance in units of proper Mpc
"""
return self.d_xy(0, z_lens) * self.d_xy(0, z_source) / self.d_xy(z_lens, z_source) * (1 + z_lens)
[docs] def T_xy(self, z_observer, z_source):
"""
:param z_observer: observer
:param z_source: source
:return: transverse comoving distance in units of Mpc
"""
D_xy = self.d_xy(z_observer, z_source)
T_xy = D_xy * (1 + z_source)
return T_xy
@property
def rho_crit(self):
"""
critical density
:return: value in M_sol/Mpc^3
"""
h = self.cosmo.H(0).value / 100.
return 3 * h ** 2 / (8 * np.pi * const.G) * 10 ** 10 * const.Mpc / const.M_sun