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assets/data/twompp_README.txt

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+
+2M++ Density and Peculiar Velocity Fields
+=========================================
+
+v1.0
+
+Please cite
+-----------
+Carrick et al. 15, MNRAS, in press.
+
+Coordinates
+-----------
+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"