|Department of Physics||University of Durham|| ||Level One|
|School of Physics||University of New South Wales|| ||General Education|
At this point you should have the following information:
Determining the Redshifts -
For each galaxy you can estimate the redshift, z from each of the spectral features you have measured, using the restframe wavelengths of the features given in the table. The redshift is simply given by:
The values of z from the different lines should be in good agreement, if they're not you have probably misidentified a feature in the spectrum - go back and take a second look. Average the different redshift estimates for each galaxy and use the scatter between the values to determine the statistical accuracy of each redshift.
Putting it all together - The figure below shows the apparent angular size of a galaxy as it relates its real physical size (D) and distance (R). We next need to convert the redshift measurements made above into recession velocities in km/sec and the angular diameters measured earlier for the galaxies in arcseconds into radians using the conversions given below. The last piece of information needed to estimate the Hubble Constant from your observations is the mean diameter of a galaxy, D. D is estimated to be typically 20 kpc using the sizes of nearby giant Spiral galaxies for which accurate distances have been measured from Cepheid variable stars. You can now estimate the Hubble Constant from each of your galaxies and then average these individual measurements together to estimate a mean value of the Hubble Constant from the sample as a whole. What is the statistical error in your measurement?
The following sections of course text books will provide background information on the astronomy discussed in this exercise.
The Extragalactic and Cosmology group in the Physics Department at Durham is one of the leading research groups in Europe tackling the properties of galaxies in the distant Universe and their formation and evolution. This research includes work on the Hubble Deep Field, gravitational lensing and theoretical work on galaxy formation and evolution. More details of the research undertaken in Durham can be found here.
Thanks to Dennis Zartisky for the original concept behind this lab and also Luis Mendoza, Doug Scott for some of the plots and text used in the background of this experiment. Also thanks to the PPARC, the Royal Society and the University of New South Wales who paid enough for me to be able to sit and write this while enjoying the sunny vistas from my window in Sydney and drinking yet more good scotch.
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