8.6 Line spectra: Activity 8 Quasar redshifts
Activity 8: Quasar redshifts
Keywords: cosmological probes, luminosity function, quasar absorption lines
Question: How can astronomers detect cool intergalactic gas in distant parts of the Universe?
By detecting redshifted absorption lines in the spectra of even more distant quasars.
As Peterson stressed in the section you have just read, high-redshift quasars are important for a variety of reasons. Consequently astronomers are currently investing time, energy and many nights of telescope usage on searching for ever more distant quasars. At the time this course was written, the most distant known quasar was that shown in Figure 29a. The identification of these distant quasars is done photometrically by looking for Lyman-break objects, where there is no detected flux in the blue part of the observed optical spectrum because it has been absorbed by high-redshift hydrogen gas, as shown in Figure 29b.