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Lab Instructions/Questions (Using CLEA)

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Lab Instructions/Questions (Using CLEA) Name: ________________________________ Date: _______________________________ LARGE SCALE STRUCTURE OF THE UNIVERSE PRE-LAB Answer each question in complete sentences. Be sure to define any relevant terms. 1. What is Hubble’s law and what does it tell us? 2. 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Your instructor will tell you which galaxies you should measure. 1. Enter the names and positions of your galaxies into table 1. 2. Move the telescope to each of your galaxies, in turn, using the set coordinates button. Record a spectrum for each galaxy as you go. Some of the dimmer galaxies will require a great deal of time to measure the spectrum. You can, by selecting Telescope from the menu bar, request time on a larger telescope. If granted, you can switch to the larger telescope at any time. If denied, you have to request again later. The larger telescopes are quite busy and do not always have available time. 3. Calculate each of the quantities necessary to fill in the chart as you proceed through your mea- surements. Record each measurement on the computer as you go. 4. When you have recorded everything, print your data to share with the class. You can use the computer to store your results for plotting. Select File and then data and save results for plot. The computer will let you know if anything is missing and will save everything to a file. You can select File, Data, Review to look at your data and make changes. PLOTTING A WEDGE DIAGRAM Your instructor will tell you how to make your data available for the project. We will begin the project by making the assumption that all of our galaxies lie at about the same declination. In other words, we are looking at a thin slice of the universe. We will plot out a graph of Right Ascension and velocity on a wedge graph. From the telescope control window of the program, select File from the menu bar. Then click on wedge plot. This will open our plotting tool. From the Plot Module window, select File and then open file. If you saved your data correctly, you should see the file listed there to be opened. Now select Plot from the menu bar and Plot current file. This should plot your data points on your graph. You can also select to enter the data points manually. This will allow you to enter points from other groups so you have a more complete graph if you did not record all of the data yourself. Once you have plotted all of the available points, you can adjust the appearance of your graph by selecting options. Your instructor may have a preferred appearance, so you should consult with him or her. When you are satisfied with the appearance of your graph, you may print it by selecting Plot and then print the plot from the menu bar. 1. Does matter in the universe appear to be randomly distributed on the large scale, or are there clumps and voids? 24–7 2. The most densely populated region of the diagram looks like a human stick figure. It is the core of the Coma Cluster of galaxies. What are the approximate Right Ascension and velocity coordi- nates of this feature? 3. You can use Hubble’s redshift-distance relation to determine the distances of objects in the chart. v = H × D where H is the Hubble constant which tells you how fast a galaxy at a given distance is receding due to the expansion of the universe. The value of H is not well known, and there is a great deal of dispute about it, but a value of 75 kilometers/sec/megaparsecs is reasonable. (1 megaparsec = 106 parsecs) Using the value of H, calculate the distance to the Coma Cluster. 4. Using the redshift-distance relation, how far is the farthest galaxy included in this study? How much smaller is this distance than the limit of the observable universe, which is about 4.6 × 109 parsecs? 5. Discuss the problem of completeness of the sample, which is based on a catalog of galaxies identified on photographs. What sorts of objects might be missing from our survey? How could we improve the completeness? 24–8 Beyond the Coma Cluster there is a loose band of galaxies stretching from east to west across the entire survey volume. It is called the “Great Wall”. 6. Using the Hubble redshift-distance relations, calculate the distance to the Great Wall. 7. One can use simple trigonometry to estimate the length of the Great Wall. If D is the distance of the Great Wall, and q is the angle it spans in the skies (in degrees), then Length of the great wall = 2/D × e / 360 Use this formula to estimate the length of the Great Wall (which is just a lower limit, since it may extend beyond the boundaries of our survey.) Give your answer in megaparsecs and light years (3.26 ly = 1 parsec). 8. What other observations do astronomers need to make to confirm that the Great Wall is indeed a wall and not just a line or filament of galaxies? 9. Attach your wedge plot to this write-up when you turn it in. 24–9 24–10 TABLE 1 REDSHIFT DATA FOR LARGE SCALE STRUCTURE OF THE UNIVERSE Name RA Dec S/N mag hK hH 6hK 6hH zK zH vK vH vavg NGC4278 12h17m36.2s 29°33’31’ TABLE 2 TARGET GALAXIES IN THE PC RESHIFT SURVEY No Name RA Dec ' " Mag vr No Name RA m s Dec ° ' " Mag vr hms° h 1 1202+3127 12 2 10 31 27 20 27 NGC 4286 12 18 12 29 38 0 2 NGC 4080 12 2 19 27 16 15 28 NGC 4308 12 19 24 30 20 0 3 NGC 4104 12 4 6 28 27 10 29 NGC 4310 12 19 54 29 29 0 4 NGC 4131 12 6 12 29 35 0 30 NGC 4314 12 20 0 30 10 0 5 NGC 4132 12 6 30 29 31 0 31 NGC 4359 12 21 42 31 48 0 6 NGC 4134 12 6 36 29 27 0 32 NGC 4375 12 22 31 28 50 6 7 1206+3151 12 6 36 31 51 0 33 NGC 4393 12 23 18 27 50 0 8 NGC 4136 12 6 48 30 12 0 34 NGC 4414 12 24 0 31 30 0 9 NGC 4150 12 8 0 30 41 0 35 IC 3376 12 25 18 27 16 0 10 NGC 4173 12 9 48 29 29
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