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PostPosted: Fri May 11, 2007 1:05 am 
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Joined: Tue Feb 20, 2007 1:10 am
Posts: 5
Location: Padova
Why can we assume that the gas related component of the galactic diffuse backgroound is locally proportional to the gas column density and we cannot assume that the ICS component is proportional to a sort of photon column density? I guess that there is a physical reason connected with the different emission processes (pion decay and bremmstrahlung and on the other hand ICS) but I cannot understand cleraly which.

Luigi


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 Post subject: IC and gas emission
PostPosted: Wed May 23, 2007 1:04 am 
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Joined: Wed May 17, 2006 7:02 am
Posts: 285
Location: MPE Garching
From the physical point of view, there is no difference (except that the
ISRF has a spectrum of course, while the gas has not).

the main practical difference is how the gas column density and the ISRF
are derived: the gas is taken directly from HI, CO surveys (as function of position) in galactocentric rings, while the ISRF is computed from a model
at every point.

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Andy Strong, MPE


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