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To Ken, Beren and Robin thanks for the feedback.
In order to make sure that there was no overlapping spectra that might introduce extraneous noise during processing of the data, the stacked image was heavily cropped to only include the 3C-373 spectrum.
I found in the heavily cropped image the emission peaks were more distinctive.
Taking on board the advice given, I recalibrated the spectrum based on a type A star.
In the attachment I have included the spectrum of a field star in the image that indicates the H-Gamma and Beta wavelengths as would be measured in 3C-273's rest frame.
The values of the red shifted wavelengths illustrated are read directly from the spectrum.
From these values the redshift z for 3C-273 are calculated as follows.
z(H-Gamma) = (502.6-434.1)/434.1 = 0.158
z(H-Beta) = (566.6-486.1)/486.1 = 0.165
z(H-Alpha) = (760.3-656.3)/656.3 = 0.158
Given that the modern value of z based on professional instruments is 0.158, I'm quite pleased with the results.
Regards
Steven
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