Red Shift Squeezing - What do the experiments show?

Question

When I read this answer to the question about the uncertainties of the redshift, I wonder whether the picture of the redshift of distant galaxies contained therein corresponds to the experimental observations. The spectra in the sketch taken from Wikipedia are simply shifted. I actually expect a squeezing of the spectra, which also grows with increasing shift. What do the experiments show?

Answer 1

The squeezing depends on the scale used to represent the spectra.

The redshift is always proportional, e.g. if a 100nm spectral line becomes 101nm, 300nm spectral line in the same redshift will get at 303nm.

If one uses a logarithmic scale for frequency or wavelength (this is pretty much reasonable if you deal with a wide spectral band related to deep cosmological redshifts, something ranging e.g. from radio to visible), the spectral pattern will stay the same and simply move over the scale.

At a linear scale of frequency or wavelength (pretty much popular in spectroscopy when dealing with a narrow spectral band, e.g. UV/visible/near infrared) your redshifted pattern will get distorted exactly the way you imagine.

This is a simple math that has little to do with the redshift itself.

(If you are interested: a redshifted blackbody spectrum remains blackbody spectrum, it just relates to lower temperature)

Answer 2

Lines in the spectra are shifted by a factor $1+z$, where $z$ is the redshift. This corresponds exactly to experimental observations. To what degree, I could not say, but it is used to identify redshifted features in galaxies with redshifts out to $\sim 10$, whose spectra are matched to templates that are modified by the uniform redshift factor above.

If there were any differences from the description above, then redshifts could not be measured, since they are based on matching a shifted pattern of spectral features.

How this shift appears in a picture depends on the scaling used on the spectrum x-axis. A uniform, multiplicative redshift appears as a uniform absolute shift if the axis is logarithmic.