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