Department of Astronomy: Quasars and Active Galaxies

Quasars & Active Galaxies

Cosmology and Star Formation History

Quasars (or quasi-stellar objects) are bright beacons at the fringes of the observable universe. The light we measure today from the most distant of these objects (at redshifts approaching 6) was emitted when the universe was <14% of its present age -- roughly 1-2 billion years old (see figure). Spectroscopic studies show that even at these early times quasars contain heavy elements (metals), presumably synthesized by local stars. These stars must have been among the first to form after the Big Bang, e.g. in the young galaxies or pre-galactic condensations that host the quasars. We are involved in efforts to measure the element abundances in quasars and thereby constrain, indirectly, the epoch and extent of star formation in the surrounding galaxies. The constraints on star formation and chemical evolution near AGNs, e.g. in galactic nuclei, will be a valuable complement to other studies of high-redshift galaxies that probe larger galactic structures or use different diagnostic tools. The main result is that quasar environments are metal-rich, with metallicities near or above the solar value even at the highest measured redshifts. Evidently, the stellar populations that contribute most to the enrichment are already substantially evolved by the time the quasars become observable. We are presently working to 1) solidify this result, 2) look for correlations with quasar luminosities and redshifts, and 3) use abundance ratios involving Fe to place better constraints on the star formation epoch. See Hamann & Ferland 1999 for a recent review of this subject, plus the other pages on this web site and the recent poster presentations by Hamann & Dietrich and Dietrich & Hamann:

Click to download the poster in a Postscript file. Click to download the poster in a Postscript file.

Redshift versus age of the universe. The 3 solid curves correspond to H_o = 65 km/s/Mpc, Omega_Lambda = 0 and Omega_M = 0, 0.3 and 1. The dotted curve assumes the same H_o but with Omega_Lambda = 0.7 and Omega_M = 0.3. The "error" bars show the range of ages for H_o between 50 and 80 km/s/Mpc.

This page created by Matthias Dietrich and Craig Warner
Questions or comments should be sent to: Matthias Dietrich

	Return to the Quasars and Active Galaxies Group Page Return to Astronomy Department Home Page