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J. Rigby, J. Charlton, C. Churchill (Penn State)
Much has been learned about the chemical and ionization conditions of the weak MgII (EWr <0.3 {Å}) intervening absorption systems found in quasar spectra. At z~1, weak MgII systems are twice as common as the strong MgII systems known to be associated with normal galaxies, but seem not to be directly associated with bright (L*) galaxies (Churchill et al., 1999, ApJS, 120, 51.) Most do not show Lyman limit breaks, which requires N(HI)<16.8 cm-2 (Churchill et al., 1999, ApJ, submitted.) Their metallicities are greater than 3 to 10% of Solar. Single-cloud weak MgII systems outnumber double-cloud systems by at least 4:1. This requires a covering factor less than ~.2, so that lines of sight, on average, encounter only one absorber.
Most weak systems contain at least two phases of gas: a
high-ionization component with Doppler parameter b~50
km/s, and a low-ionization component with 2
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