This program calculates R200 in degrees given the central velocity and velocity dispersion.
In [27]:
from astropy.cosmology import FlatLambdaCDM
import numpy as np
cosmo = FlatLambdaCDM(H0=70, Om0=0.3)
OmL=.7
Om0=.3
H0=70.
def getr200(recessionvel,sigma):
redshift=recessionvel/3.e5
r200=2.02*(sigma)/1000./np.sqrt(OmL+Om0*(1.+redshift)**3)*H0/70. # in Mpc
r200deg=r200/cosmo.angular_diameter_distance(redshift)*180./np.pi
return r200deg.value