tweak_redshift

threadcount.fit.tweak_redshift(cube, z_gal, center_wavelength=5006.843, wavelength_range=(-15, 15), pixel_mask=None)[source]

Interactively choose a new redshift.

This procedure has several steps.

  1. Select which spaxels to use for calculating the redshift via one of these options:

  • use the input parameter pixel_mask

  • Select pixels with a high integrated flux value in the selected wavelength range. These are likely to be the galaxy. The user will interact with the terminal and view a plot to interactively change the lower threshold for the desired pixels. To accept the value plotted, leave the entry blank and press enter.

  1. Fit a Const_1GaussModel to the selected spaxels.

  2. Extract the parameter value for ‘g1_center’ to get the center wavelength of the fitted gaussian and compute the median center.

  3. Calculate the redshift required for the median center to be equal to center_wavelength using the formula:

    new_z = (median_center / `center_wavelength`) * (1 + `z_gal`) - 1

  4. Display a plot showing the spaxels used and a histogram displaying all the center wavelengths (with center_wavelength subtracted, so it displays the change from ideal)

Parameters:

  • cube (mpdaf.obj.Cube) – A datacube containing the wavelength range set in these parameters

  • z_gal (float) – The redshift of the object which has already been applied to the cube

  • center_wavelength (float, optional) – The center wavelength of the emission line to fit, by default threadcount.lines.OIII5007

  • wavelength_range (array-like [float, float], optional) – The wavelength range to fit, in Angstroms. These are defined as a change from the center_wavelength, by default (-15, 15)

Returns:

The redshift selected by the user.

Return type:

float