Unit Conversion

From: Brad Krane <brad.krane_at_gmail.com>
Date: Mon, 14 Aug 2006 21:34:18 -0400


I am trying to convert an IC file that has the positions and
velocities in physical units to the Gadget2 format. I have converted
the the positions from physical to comoving units by multiplying by h.
Doing this yields obviously correct results. In converting the
velocities however this is not as obvious. In using the formula given
on page 32 of the Gadget2 documentation that v=u*sqrt(a) where v is
the physical velocity, u is the internal units and a=1/(1+z) gives
obviously incorrect results as the evolution of the system at z=0
looks more like an evolution of a system to z=3 give or take a good
bit. If I however use the formula that v=ua the results seem much more
reasonable though I am not entirely convinced that this is correct by
a simple visual inspection. Are the velocity units in Gadget2 comoving
(the documentation only specifies that velocities in Gadget2 are in
internal units) or is there an additional subtilty?

Received on 2006-08-15 03:34:21

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