16.2.1 From Flux density to Brightness temperature

The unit of the dirty map is ill defined. A single point source of 1 Jy appears with peak intensity of 1. But if more than 1 point source is in the field of view, the combination of positive or negative sidelobes from the other source modify this result. It is thus necessary to deconvolve. After deconvolution, the beam area is well defined: the CLEAN map unit is Jy per beam area.

The conversion to brightness temperature can then be done using the standard equation

$$S_\nu \frac{2 k \ensuremath{\Omega_\mathrm{\scriptscriptstyle s}} }{\lambda^2} T_B$$ = (16.1)

$$\frac{2 k \pi \ensuremath{\theta_\mathrm{\scriptscriptstyle s}} ^2}{4 \log{2} \lambda^2} T_B$$ = (16.2)

for Gaussian beams. GO MAP and its variants automatically display the Jy/K conversion factor mentioned above. The integrated flux density in a user defined area can then be computed on the clean map using command GO FLUX.