Space Warps Talk

Confusing paragraph in Spotter's Guide

  • Kelvets by Kelvets

    In the following page: http://spacewarps.org/#/guide

    One of the paragraphs is:
    "If you look at the examples below you'll probably have already noticed that the lensed or distorted images tend to be blue rather than the yellow/red of the lensing galaxy. This is partly because more distant galaxies are more likely to be young and so they have a lot of young stars that predominantly create more energetic photons or blue light. In addition, distant galaxies are "redshifted" this means the light you actually see originated from a shorter or bluer wavelength. Hence distant galaxies tend to look blue. While this is typically true for most of the lenses you will see, if these objects are at very high redshift, it can be that the bright blue photons that are emitted are so far away that they actually arrive at earth at even longer wavelengths. These images will appear red in our colour composites. So don't reject red arcs or images - these could just be at high redshift!. There's an example of a high-redshift lensed quasar in lensed quasars."

    I have read this multiple times and found it to be rather confusing and ambiguous. It could be better written. I broke it down into sections to explain what I mean.

    Section 1: ""If you look at the examples below you'll probably have already noticed that the lensed or distorted images tend to be blue rather than the yellow/red of the lensing galaxy. This is partly because more distant galaxies are more likely to be young and so they have a lot of young stars that predominantly create more energetic photons or blue light." No problem here. More distant galaxies look bluer because they have younger stars which emit more energetic photons, which are of a shorter wavelength, hence bluer.

    Section 2: "In addition, distant galaxies are "redshifted" this means the light you actually see originated from a shorter or bluer wavelength." I would suggest adding an 'even' before 'shorter' to reinforce that the light you see from the redshifted galaxy still looks blue, it didn't become red despite being redshifted. Plus, the word 'actually' serves no purpose and makes the text look less professional.

    Section 3: "Hence distant galaxies tend to look blue." This phrase is in the wrong place. It should come immediately after Section 1 and immediately before section 2 (in between both sections, that is), because it reinforces what was explained in Section 1.

    Section 4: "While this is typically true for most of the lenses you will see, if these objects are at very high redshift, it can be that the bright blue photons that are emitted are so far away that they actually arrive at earth at even longer wavelengths." The 'even longer wavelengths' bit is the problem here, because blue light has (relatively speaking) short wavelength! Thus it cannot be "even longer" because it was never long to begin with. I suggest changing the section to '(...) are so far away that they become red.' Also, I recommend taking the "actually" out once again.

    Thoughts?

    Posted