I am trying to do kinematical analysis of spectra using ppxf-algorithm from Capellari. The velocity dispersion I get seems to be to high and I am not sure what the reason could be. On the website of the ppxf algorithm ( https://pypi.org/project/ppxf/#problems-with-your-first-fit), he suggests to plot galaxy spectra and template convolved with gaussian and try to make the parameters roughly fit by eye, which I tried:

   sigma = 6  # Velocity dispersion in pixels
shift = 40  # Velocity shift in pixels
flux_temp = np.roll(ndimage.gaussian_filter1d(flux_temp, sigma), shift)
plt.plot(loglam_gal,flux_gal, 'k', label ='galaxy')
plt.plot(loglam_temp, flux_temp * np.median(flux_gal) / np.median(flux_temp), 'r', label='template convolved with gaussian')

Resulting in the plot:

enter image description here

In the middle arround the Mg-triplet this is roughly a good match I would say, on the outer parts not so much. Just looking at the plot, are there any concerns about the applicability of the ppxf-algorithm ?



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