Examine the image of the Hubble Deep Field (HDF) below. (By deep, astronomers mean dim and distant!) The HDF takes us far out into space and far back in time to see some of the faintest objects ever detected, about 4 billion times fainter than the naked human eye can see. The image contains thousands of galaxies of many shapes and colors. To create it, the Hubble Space Telescope exposed its electronic detectors for about 100 hours over the course of 10 days, pointed at a tiny region of space near the Big Dipper. The amount of sky in the image is about the same as the size of a tennis ball at a distance a little over 100 yards, an area about 1/100 of the full Moon.
Use this file to print the image of distant galaxies. As you record each of the galaxies with a redshift, mark it off on the printed copy so you know which ones you have already recorded.
After this image was obtained, the 10-meter Keck telescope in Hawaii observed the faint blue galaxies in the image to measure their redshifts. Next to many of the galaxies in the HDF is that galaxy’s redshift, z, (except for a few cases, the corresponding galaxy is usually the galaxy located to the upper left of the redshift number).
Since the redshifts of objects are related to their distances, we can examine the actual distribution of galaxies in this direction in the sky using a histogram.
If you need a review of how to construct a histogram or to see some examples of histograms, take a look here:
In our case, our bin size is 0.1 in redshift and there are too many galaxies to count visually how many have redshifts between, say, 2.2 and 2.3. Instead, for each galaxy with a measured redshift, put an “X” corresponding to its redshift in the histogram plot in the worksheet. The goal is to see how galaxies are distributed as function of redshift.
Examine the distribution of galaxies as a function of redshift, or distance. Are the galaxies smoothly distributed at all redshifts (distances), or are they clumped together at a few specific distances? What do these data suggest about how matter is distributed in the universe? Is it smoothly distributed or clumpy? Do galaxies fill most of space, or are there vast, empty spaces between groups of galaxies?
After you have recorded each of the redshifts on the histogram, answer the questions on the worksheet.