Notes on Large Scale Universe ASTRO 11 - Large Scale...

A Manual to Accompany Software for
the Introductory Astronomy Lab Exercise
Document SM 7: Version 1
Department of Physics
Gettysburg College
Gettysburg, PA 17325
Telephone: [phone]
email: [email protected]
Contemporary Laboratory
Experiences in Astronomy
Large Scale Structure of the Universe
Student Manual

Contents
Goal ...................................................................................................................................................... 3
Objectives ............................................................................................................................................ 3
Equipment and Materials .................................................................................................................. 4
Background: The Large-Scale Distribution of Matter .................................................................. 4
Introduction to the Technique ........................................................................................................... 5
Overall Strategy ............................................................................................................................................................. 5
Technical Details ........................................................................................................................................................... 6
Taking Spectra With the CLEA Computer Program ...................................................................... 7
Beginning Your Observations ........................................................................................................................................ 7
TABLE 1: Redshift Data For Large Scale Structure Exercise .................................................... 12
Calculating Redshifts ....................................................................................................................... 13
Recording Data On the Computer .................................................................................................. 13
Collecting Data for a Wedge Plot .................................................................................................... 14
Plotting the Pooled Data On A Wedge Plot .................................................................................... 15
Pooling your data ......................................................................................................................................................... 15
Plotting your data on a wedge diagram ....................................................................................................................... 16
Interpreting the Wedge Plot ............................................................................................................ 17
Concluding Remarks ........................................................................................................................ 19
Useful References .............................................................................................................................. 19
TABLE 2: Target Galaxies In the PC Redshift Survey ................................................................. 20
Appendix I ......................................................................................................................................... 28
Reviewing and Editing Data ........................................................................................................................................ 28

Version 1.0
P
AGE
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Goal
You should be able to use observations of the redshifts of galaxies, along with their coordinates in the sky, to produce
a three-dimensional map of a nearby region of the sky. You should understand how matter is distributed on the
largest scales in the universe. You should appreciate some of the difficulties involved in making and interpreting
large-scale maps of the universe.
Objectives
If you learn to .........
Find galaxies in a restricted area of the sky using a list compiled by earlier observers.
Take spectra of these galaxies using simulated telescopes and
spectrometers.
Recognize the principal features of galaxy spectra.
Measure the wavelengths of principal spectral lines in galaxies.
Calculate the redshift, z, and the radial velocities of the galaxies.
Plot radial velocities and positions on a wedge diagram.
Interpret the distributions of galaxies you see on the wedge diagram.
You should be able to .........
Tabulate the radial velocities of all 218 galaxies in your sample.
Produce a map of the three-dimensional distribution of galaxies in a small part of the universe near our own
Milky Way galaxy.
Develop an understanding of the typical sizes of large-scale features (superclusters and voids) in universe.
Appreciate some of the difficulties and limitations of such measurements.
Useful Terms you should review using your textbook
absolute magnitude Declination Hubble Constant radial velocity superclusters
absorption lines distance modulus Hubble relation redshift wavelength
Angstrom (Å) Doppler Shift local group Right Ascension wedge diagram
apparent magnitude elliptical galaxy megaparsec spectrometer z
Ca H and K galaxy parsec spectrum
Coma cluster galaxy cluster photon spiral galaxy