Department of Physics University of Durham   Level One
School of Physics University of New South Wales   General Education

Measuring the Hubble Constant


 Redshift Measurement - Measure the redshifts for the 15 galaxies for which you previous measured diameters on the last page. When you click the cursor the program will draw a line on the image showing the wavelength you selected and output the wavelength in Angstroms (Å). You can also use the LEFT and RIGHT arrow keys to make fine movements of the cursor. To move between the different spectra use the UP and DOWN arrow keys. The measured wavelength is written both at the top of the image (for the current spectrum) and should also all be listed on the Java console of your browser. In each case you should repeat the measurements for the different galaxies to try to gauge your measurement errors. The ratio of the observed wavelength of a spectral feature to its restframe wavelength (from this table) gives the redshift for the galaxy. By averaging redshift estimates from a number of features in each spectrum you should be able to accurately measure the galaxy's redshift. When you are satisfied that you have robust measurements for the wavelengths of features in all 15 galaxies, and estimates of the errors on these values, then move onto the calculation stage of this exercise on the next page.

Warning: the spectra below use a java script for their display. This can be slow to load, and java can also get itself in a mess if you try to type ahead too much. Wait for each spectrum to load *completely* before trying to look at the next on. Be patient and work slowly if you want to achieve results! I'm afraid there is still some program development to go for these applications

HDF galaxy redshifts


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