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Session 72 - Cosmic Rays and Abundances.
Oral session, Thursday, June 11
We present two Lyman-\alpha forest clouds that either have super solar abundances or contain a local ionizing source with an effective temperature of at least 5 \times 10^4 K. The systems were found in high signal-to-noise QSO spectra from Keck+HIRES. The simple, unsaturated H I and C IV profiles show N(C IV)/N(H I) \gtrsim 1 in both systems. Both systems are separated from the QSO emission redshifts by over 3 \times 10^4 km s^-1, and have proper C IV doublet ratios which require full covering factors. The resolved H I Lyman-\alpha lines constrain the temperatures to T < 1.5 \times 10^4 K. The high C IV/H I ratios require super solar abundances if the systems are photoionized by the ultraviolet extragalactic background. The abundances may be subsolar, but that scenario requires a local source of ionization with an effective temperature T_eff > 5 \times 10^4 K. Either case suggests high star formation at high redshift, the former gives rise to medium-scale (> 100 h^-1 kpc) inhomogeneous metal production and the latter to the presence of very massive stars at high redshift.
Program listing for Thursday