AAS Meeting #194 - Chicago, Illinois, May/June 1999
Session 63. Evolution of Chemical Abundances over Cosmic Time
Topical, Oral, Wednesday, June 2, 1999, 8:30-10:00am, 10:45am-12:30pm, 2:00-3:30pm, 3:45-5:30pm, Continental Ballroom A

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[63.07] Probing Metallicities at High Redshifts with Quasar Absorption Line systems

A. M. Wolfe (U. of California, San Diego)

Measurements of metal abundances in QSO absorption systems provide a window into cosmic chemical evolution at high redshifts. The Lyman alpha forest clouds, where logN(HI) > 14, have metallicities, Z/Zsolar ~ 0.01, and even lower values for clouds with logN(HI) ~ 13.5. In the damped Lyman alpha systems (DLA), where logN(HI) > 20.3, the mean Z/Zsolar= 0.07 with individual objects in the range Z/Zsolar = (0.01,0.5) at redshifts z = (0.5,3.0). At z > 3, the mean metallicity appears to decrease below 0.07. Attempts to explain these trends by chemical evolution of isolated galaxies undergoing passive evolution do not work since they predict a systematic increase of the mean Z/Zsolar with time which is not observed. Rather, the observed trends are better explained in the context of hierarchical cosmologies by identifying DLAs as regions of high comoving density in which the mean Z/Zsolar rapidly approaches solar values at high redshifts and saturates thereafter, and the Ly\alpha forest clouds as regions of low comoving density in which the mean Z/Zsolar catches up more slowly (Cen & Ostriker 1999).

Finally, I examine abundance patterns in DLAs to search for clues as to how and where the metals formed. I also look at the relationship between metallicity and kinematics which may provide insights into the nature of the DLAs

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