First we show in Fig. 1 (click here) the spectrum of the average optical depth across the source; this corresponds roughly to single-dish observations. Low level features are enhanced by giving a scaled-up version of the profile (thin line).
Figure 1: Average optical depth spectrum of Cas A. The thin line is the
spectrum scaled by a factor 5
The display of a large data-cube
without colour is a well-known difficulty.
Three main displays are utilized, with all intensities as optical depths:
(i) Fig. 2 (click here) shows "channel images'', i.e. images in right ascension and declination
for adjacent velocities. Optical depths below the (one sigma) error limit
were omitted; these uncertainties are displayed as an error map in the
second panel. The third panel is a map of the "equivalent width'' in HI,
, which can be used for correlations with X-ray data, etc;
the units are km s
.
(ii) In Figs. 3 (click here) and 4 (click here) we show velocity-right ascension images (horizontally the velocity,
vertically the right ascension) for a series of declinations, for two velocity
ranges.
(iii) Figs. 5 (click here) and 6 (click here): Series of spectra arranged in the same order as in the
velocity-right ascension maps.
All figures are based on coordinates of right ascension and declination. Galactic coordinates are included in Fig. 9 (click here).