Exploring the Relationship between Reddening & Distance

The expansion of the Universe causes light waves to be stretched to longer wavelengths. The actual galaxy colors do not change, but from our vantage point on Earth they appear to become redder when their light is stretched to longer wavelengths. This stretching is called cosmological redshift.

Here are the data for all of the galaxies you selected in the Rubin Observatory deep field image, plotted by their redness vs distance.

The color of a galaxy may be converted into a numerical value by using a flux ratio, which is a comparison of how bright the galaxy appears through two different filters (in this case, it compares the galaxy brightness through the i filter to its brightness through the z filter). Smaller flux ratio numbers means the light from the object being observed appears redder.