ra_dec_z¶
- halotools.mock_observables.ra_dec_z(x, v, cosmo=None)[source]¶
Calculate the ra, dec, and redshift assuming an observer placed at (0,0,0).
- Parameters:
- x: array_like
Npts x 3 numpy array containing 3-d positions in Mpc/h
- v: array_like
Npts x 3 numpy array containing 3-d velocities in km/s
- cosmoobject, optional
Instance of an Astropy
cosmology
object. The default is FlatLambdaCDM(H0=0.7, Om0=0.3)
- Returns:
- ranp.array
right accession in radians
- decnp.array
declination in radians
- redshiftnp.array
“observed” redshift
Examples
For demonstration purposes we create a randomly distributed set of points within a periodic unit cube.
>>> Npts = 1000 >>> Lbox = 1.0 >>> period = np.array([Lbox,Lbox,Lbox])
>>> x = np.random.random(Npts) >>> y = np.random.random(Npts) >>> z = np.random.random(Npts)
We transform our x, y, z points into the array shape used by the pair-counter by taking the transpose of the result of
numpy.vstack
. This boilerplate transformation is used throughout themock_observables
sub-package:>>> coords = np.vstack((x,y,z)).T
We do the same thing to assign random peculiar velocities:
>>> vx,vy,vz = (np.random.random(Npts),np.random.random(Npts),np.random.random(Npts)) >>> vels = np.vstack((vx,vy,vz)).T
>>> from astropy.cosmology import WMAP9 as cosmo >>> ra, dec, redshift = ra_dec_z(coords, vels, cosmo = cosmo)