Datacube fitting

Using IFSCUBE to fit emission lines in data cubes is very similar to fitting a single spectrum, which is described in section Single spectrum fitting. To start the fitting process you must call the cubefit executable script from the command line.

cubefit -c halpha_cube.cfg ngc3081_cube.fits

Here we are using the provided example files distributed with ifscube.

For more information on the available command line options of cubefit, please read the help page printed by

cubefit -h

Configuration file

There are only minor differences between the configuration files of specfit and cubefit, which will be covered in the following subsections, each relating to a particular section of the configuration file. Please refer to section Single spectrum fitting for parameters and options that also apply to single spectrum fitting.

fit

  • bounds_change: <change_par_0>, <change_par_1>, …
    When using refit (see below), set the bounds to these distances from the nearby successful fits. The values are all aditive, with the exception of the amplitude (always the first parameter), which is a ratio. For instance, if you want the amplitude to change by at most half the current value, the velocity to change by at most 30 km/s and the velocity dispersion by 20 km/s, you would write “0.5, 30, 20”.
  • individual_spec: ‘no’, ‘x, y’, ‘peak’ or ‘cofm’
    If set to no fits all the spectra in the data cube, else fits only one spectrum. If set to x, y fits the spectrum in the spaxel with horizontal coordinate x and vertical coordinate y. peak will fit only the spaxel with the highest value in an image resulting from the sum of all the pixels along the dispersion direction. cofm is similar to peak, but uses the center of mass instead.
  • refit: ‘yes’, ‘no’
    Uses parameters from previous successful fits as the initial guess for subsequent fits. The parameters are the average of the results for fits returning a fit_status of 0 within a given refit_radius.
  • refit_radius: float
    Radius in pixels to use when averaging parameters for the updated initial guess.
  • spiral_loop*: ‘yes’, ‘no’
    Fits the spaxels following a spiral pattern from the specified spiral_center outwards. This is particularly useful when refit is set to ’yes’, since the algorithm will start from the highest signal to noise ratio spectra.
  • spiral_center: ‘x, y’, ‘peak’ or ‘cofm’
    Chooses where the spiral pattern will start. See individual_spec above for a description of the meaning of ‘x, y’, ’peak’ and ‘cofm’.