[daip] RMS flux density per pixel

[Eric Greisen]

Modhurita Mitra wrote:
> Thank you Eric. I need the RMS flux density per pixel to calculate the 
> error in the source flux density obtained by placing a bounding box 
> around the source and computing the integrated flux inside the box using 
> IMSTAT. The expressions I am using are:
> 
> Off-source RMS flux density per pixel = (Off-source RMS flux density in 
> Jy/beam)/(Number of pixels/beam)
> Error in source flux density = (Off-source RMS flux density per 
> pixel)*sqrt(Number of pixels in bounding box around the source)
> 
> Are these correct? Yes, I am aware that the errors in adjacent pixels 
> are correlated but I am neglecting that for the moment.

Given that a beam is usually 20 pixels, I do not thin you can ignore the 
correlation.  It would be more accurate to use off-source rms in Jy beam 
times the sqrt of the number of beams in the area.  The explain files 
for IMFIT (JMFIT or SAD) have a discussion of these uncertainties also.

Eric Greisen