Quasar Absorption Lines


The spectrum of the quasar Q1425+6039 shown above was obtained with the High Resolution Echelle Spectrograph (HIRES) on the Keck I Telescope. This instrument has revolutionized the study of the absorption lines observed in the spectra of quasars. The quasar has an emission redshift of z = 3.18. To the left of the Lyman alpha emission line you see the "forest" of H I absorption lines produced by intervening, tenuous intergalactic clouds. (For a review see M. Rauch "The Lyman Alpha Forest in the Spectra of QSOs'' .) The particularly strong line at 4650 A is a "damped Lyman alpha" absorption feature at a redshift of z = 2.82 produced in a cloud which is optically thick in H I. Many of the weak absortion features on the long wavelength side of the Lyman alpha emission line are low ioization lines of heavier elements (O I, Si II, C II, etc. ) associated with this system. Other features are C IV and Mg II resonance doublets produced in the halos of intervening galaxies.

Most of what we know about the physics and composition of the intergalactic medium and the interstellar gas in galaxies has come from analyses of quasar absorption spectra like the one shown.


I am collaborating on the study of quasar absorption spectra principally with M. Rauch (OCIW), G. Becker (OCIW) and B. Penprase (Pomona College). The following are some of our recent papers on quasar absorption lines:


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page by Wallace Sargent, last updated 13 March 2008