2M++ Density and Peculiar Velocity Fields
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v1.0
Please cite
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Carrick et al. 15, MNRAS, in press.
Coordinates
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The density and peculiar velocity fields are both 257^3 cubes using
the same coordinate system: configuration ("real") space
(reconstructed so that the peculiar velocities are removed iteratively
as described in Carrick et al 15), and smoothed with a Guassian of
scale 4 Mpc/h.
Specifically i,j,k index the 257^3 data cube in Galactic Cartesian
comoving coordinates X,Y,Z in Mpc/h, with i running fastest. The cell
centres run from -200 to 200 Mpc/h so the grid spacing is 1.5625 Mpc/h
To convert Galactic X,Y,Z use:
X = (i-128)*400./256.
Y = (j-128)*400./256.
Z = (k-128)*400./256.
The centre of the cell [0,0,0] therefore corresponds to -200,-200,-200
and the origin (Local Group) is in the centre of cell [128,128,128].
The density delta_g^* is the luminosity-weighted density contrast.
The velocities are predicted peculiar velocities in the CMB frame in
Galactic Cartesian coordinates, generated from the delta_g* field with
beta* = 0.43 and an external dipole Vext = [89,-131,17] (Carrick et al
Table 3) has already been added.
# Sample Python 2.7 code to read 2M++ data
import numpy as np
# LG is in central voxel at 128,128,128
d = np.load('twompp_density.npy')
print "Overdensity at LG is:", d[128,128,128]
v = np.load('twompp_velocity.npy')
vlg = v[:,128,128,128]
print "LG's motion in Galactic:", vlg
print "Velocity:", np.sqrt(vlg.dot(vlg)), "km/s"