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velcube - create a data cube from a velocity field


velcube [parameter=value]


velcube creates a theoretical position-position-velocity data cube with signal derived from a velocity field (required) surface density and velocity dispersion map (both optional).


The following parameters are recognized in order; they may be given in any order if the keyword is also given. Use --help to confirm this man page is up to date.
Output file name (a cube) in image(5NEMO) format. The X,Y coordinates will be inherited from the input velocity field, the Z coordinates set via nz= and zrange= (see below). No default.
Input velocity field. No default. This map
Input surface density (optional). Should be 0 or positive Negative densities are skipped and reported.
Input velocity dispersion map (optional). Should be 0 or positive Negative dispersions are skipped and reported. Zero dispersion amounts to only 1 slice to be populated.
Range in (Z) velocity. The lower value must really be lower than the higher value. [-2:2].
Number of gridding pixels in Z [64]
Default (constant) velocity dispersion in case no dispersion map is given. [0].


A model velocity field can be easily made with ccdvel(1NEM0) , and using the amp=t keyword density and dispersion (sigma) maps can also be created. Another way to create a smooth velocity field is using rotcurshape(1NEMO) using a 0 input map and fixing all fittable parameters. The resulting output residual map then contains -1 times the desired velocity field.

  nemoinp 0:100:1 > map1.radt
  tabmath map1.radt - "%1/sqrt(40+%1*%1)" all > map1.velt
  ccdvel out=map1.vel radii=@map1.radt vrot=@map1.velt pa=30 inc=60 size=256

Here is an example of creating a (0/1) mask cube based on where you expect emission from a rotating disk given the geometry

ccdvel out=$tmp.d radii=0,$r0,$r1 vrot=1,1,1      inc=$inc pa=$pa size=$nx
cell=$cell amp=t
ccdvel out=$tmp.v radii=0,$r0,$r1 vrot=0,$v1,$v1  inc=$inc pa=$pa size=$nx
cell=$cell amp=f vsys=$vsys
ccdvel out=$tmp.s radii=0,$r0,$r1 vrot=100,100,50 inc=$inc pa=$pa size=$nx
cell=$cell amp=t
velcube - $tmp.v $tmp.d zrange=${vsys}-5*${nz}:${vsys}+5*${nz} nz=$nz sigdefault=$sig
  ccdmath - -  ’ifgt(%1,0,1,0)’ |\
  ccdfits - $mask refmap=$refmap refaxis=1,2,3 crpix=$nx/2,$nx/2,$nz/2 cdelt=-$cell/3600,$cell/3600,$chan

where a $refmap was used to inherit the WCS from.

See Also

ccdvel(1NEMO) , ccdmath(1NEMO) , rotcurshape(1NEMO)




Peter Teuben

Update History

29-May-04    V1.0 Created    PJT
6-may-2021    Add full example    PJT

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