velmoment - Builds a velocity map from a three-dimensional IFU NDF from the intensity-weighted spectral co-ordinates

Description:

This shell script processes a three-dimensional IFU NDF to form a velocity map.

If you request zooming the script first presents you with a white-light image of the cube. You can then select the lower and upper spatial limits to plot using the cursor. You can instead supply an NDF section with the filename to define both spatial and spectral limits to analyse, and from which to create the output velocity map. You may average spectra in the chosen region by specifying compression factors in the spatial domain.

The script then derives the intensity weighted co-ordinate of each spatially averaged spectrum, and converts the data units into a velocity. You may view this image drawn with a key (option -d), and overlay a contour plot of the white-light image (option -c).

Usage:

velmoment [-b string] [-c number] [-ci index] [-i filename] [-o filename] [-p] [-r number] [-s system] [-z/$+$z]

Command-line Arguments

• -b string
  The number of spectra to block average along the $X$ and $Y$ axes respectively. This should be a comma-separated list or a single number; the latter case applies the same compression factor to both spatial axes. The numbers must be positive integers. [1]

• -c number
  Number of contours in the white-light image. Set to fewer than one means no contours are overlaid. [15]

• -ci index
  The palette colour index of the contours. It should be an integer in the range 0 to 15. It is best to choose an index corresponding to white, or black or another dark colour to make the contours stand out from other elements of the plot. 0 is the background colour. KAPPA:GDSTATE will list the current palette colours. [0]

• -i filename
  The script will use this as its input file, the specified file should be a three-dimensional NDF. By default the script will prompt for the input file. If there are multiple spectral lines present, you should supply an NDF section after the name to restrict the spectral range analysed to a specific line and its environs.

• -o filename
  The filename for the output NDF of the velocity map.

• -p
  The script will plot the final image map to the current display as well as saving it to an NDF file. Additionally it will over- plot the white-light image as a contour map for comparison. [FALSE]

• -r number
  Rest-frame spectral unit of the line being fitted.

• -s system
  The co-ordinate system for velocities. Allowed values are:

  "VRAD"

  - radio velocity;

  "VOPT"

  - optical velocity;

  "ZOPT"

  - redshift; and

  "VELO"

  - relativistic velocity.

  If you supply any other value, the default is used. ["VOPT"]

• -z
  The script will automatically prompt to select a region to zoom before prompting for the region of interest. [TRUE]
  +z
  The program will not prompt for a zoom before requesting the region of interest. [FALSE]

Notes:

• The compression is trimmed, so that only compression-factor multiples of original pixels are included in the plot.

• The spatial averaging is aligned to obtain the expected number of pixels irrespective of the pixel origin of the input cube. Note that this may not be suitable if you wish to preserve alignment with another compressed dataset. See KAPPA:COMPAVE parameter ALIGN for more details.

• The velocity map display scales between the 2 and 98 percentiles. The map uses a false-colour spectrum-like colour table so that low-velocity regions appear in blue and high-velocity regions appear in red.

• If the cube is compressed spatially, so is the contour map.

• For NDFs in the UK data-cube format, where there is no SPECTRUM or DSBSPECTRUM Domain in the WCS Frames, the data are first collapsed in their native wavelengths in Ångstrom, then the pixel values are converted to VOPT using the simple formula $c(\lambda-\lambda_{0})/\lambda_{0}$, where $\lambda$ is the intensity-weighted wavelength, $\lambda_{0}$ is the rest-frame wavelength for the chosen spectral line, and $c$ is the velocity of light in km s$^{-1}$.

Implementation Status:

This script invokes a collection of A-tasks from the KAPPA package.