Hi Geoffrey,
  the deal with both SZY and SZKinetic (in the real universe) is that they are equal to the Compton y parameter, and the "b" parameter respectively.  Both should be, in this implementation, unit free.  SZY is essentially the probability of scattering on the sight line, and is proportional to the value of deltaT/T_cmb.  Similarly SZKinetic (I think in yt) is equal to the b value of the kinetic effect, which is unit free, and is also proportional to deltaT/T_cmb.  In fact, if I remember right for SZKinetic, the constant of proportionality is 1.  So the cgs units of SZ parameters result in no units.

Hope that helps.


On Jun 25, 2012, at 9:10 PM, Geoffrey So wrote:


I'm trying to plot a projection of the SZ effect, and I'm not sure how the mechanism works.  If I do
proj = pf.h.proj(0, "SZKinetic", weight_field='Ones')
frb = FixedResolutionBuffer(proj, (0.0, 1.0, 0.0, 1.0), (imgres, imgres))
img = frb[field]
pylab.imshow( img, interpolation='nearest', origin='lower') 

After some digging I found the constants defined in yt/utilities/physical_constants.py, but I'm not sure how do I use the convertSZKinetic to get cgs answers (is the field SZKinetic already returned as cgs, if so what is the cgs units?), and what are the units on 0.88 in the following equation?  If I know that I can figure out the cgs units.

def _convertSZKinetic(data):
    return 0.88*((sigma_thompson/mh)/clight)

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