After correcting for primary beam attenuation with PBCOR, the noise in the images will depend upon position. Because of this, you should use the uncorrected line cube for moment analysis.
(34) | The frequency axis can be labeled in either frequency or velocity units. Make sure that the desired units are chosen; use IMHEAD to check. Velocity is recommended for moment analysis. |
(36) | Generate images of the total emission (MOM0), the velocity field (MOM1), and the line width (MOM2) using the transposed cube as input. Be sure to exclude the end channels as they generally are very noisy. Try various values for the flux cutoff FLUX and the width of the smoothing functions (set by CELLSIZE) until you are satisfied with the results. |
(37) | Correct for the attenuation away from the center of the primary beam in the MOM0 image, as in Step 28. If you computed the moment images with a velocity axis, use ALTSW to change to a frequency axis before running PBCOR. |
(38) | Make contour plots of the MOM0 and MOM1 images; see Step 24. Note that KNTR can superpose contour and grey-scale plots as in Figure 8.4. |
(39) | The task GAL allows you to generate a “tilted-ring” model rotation curve of two types from a galaxy’s velocity field or to fit single-parameter rotation curves to annuli of a specified width. The EXPLAIN file for this task describes all of the parameters in detail and contains general advice on how to obtain an optimum fit. |