Refresher on Lyman Break and It's purpose in Astrophysics

The Lyman Break plays an important part in astronomy.  Generally, it allows us to visualize and analyze the galaxies redshift. However, we must understand what it is!

The Lyman limit ranges from 91 nm to 121.5 nm for the element Hydrogen. It represents the energy needed to eject an electron completely from a hydrogen atom. Any energy (photons) that have a shorter wavelength (higher energy) than 91 nm will be absorbed by the atom. 

In the Universe, the majority of the stars are filled with hydrogen cannot emit light that is much more energetic than the Lyman limit. The Lyman limit is found within the ultraviolet region of the electromagnetic spectrum. This can change due to redshift (which we will discuss later!). 

In the Universe, there are interstellar and intergalactic clouds of neutral hydrogen. When energy emitted carrying photons with longer wavelengths (>91 nm) comes into contact with this neutral hydrogen, a sharp cutoff (or break) in the stellar emission spectrum occurs at 91 nm. The bottom line is that light from normal galaxies has a sharp cutoff at the 91 nm wavelength, when viewed from a great distance.

So, shouldn't every single galaxy viewed from earth have a Lyman break identified at 91 nm? 

No, because redshift changes everything when it comes to light traveling in the constant stretching of "space fabric". Redshift, is the shifting of spectral lines, or stretching of wavelengths into the red part of the spectrum. The higher the redshift, the more these spectral lines have been shifted. 

The Universe is expanding, and everything is moving away from The Milky Way (Except for the nearby Andromeda Galaxy). So, technically everything in space is getting redshifted depending on their closeness to the Milky Way. For example, a nearby galaxy is not moving away from us as fast a galaxy that is far far away. So, the redshift is a cause of the Doppler Effect.

So, going back to the question that should every single spectral source have a Lyman break around 91 nm. The redshift or expansion of the universe causes this Lyman limit and it's break to shift to the red part of the spectrum. So, for example, a galaxy with a redshift of 3 will have it's Lyman break found around a wavelength of 364 nm rather than 91. Another example is that a galaxy with a redshift of 8 will have it's Lyman break around 1000 nm. 

We can use a galaxies Lyman Break to figure out it's redshift, and with it's knowledge of the redshift, we can find out the age of the universe the galaxy was present in. Through the use of filters present on the Hubble Space Telescope, we can see where the galaxy "pops up". So if we can't see the galaxy on a filter that allows wavelengths of 814 nm and below to pass through, but we suddenly see it in a filter that allows wavelengths of 1125 nm and below to pass through, we understand that the galaxy's Lyman break is in between 814 and 1125 nm. So roughly we can guess that the Galaxies redshift is around 7-8.

We can find out the galaxies redshift through the use of the Wavelength-Redshift equation. 

Comparing the actual Lyman limit in the ultraviolet region (without the redshift) 91 nm, we can compare it to the observed wavelength (for this example lets say 969 nm). So it would be 1 + Z = (969 nm / 121 nm). Z, representing redshift, would be around 9.

Using Ned Wright's Cosmological Calculator : http://www.astro.ucla.edu/~wright/CosmoCalc.html , The universe was around 550 million years old when the galaxy was observed. This supports the claim that this galaxy with a redshift of 9, was a early galaxy.