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J. Ding, C.W. Churchill, J.C. Charlton, S.G. Zonak (Penn State)
The z=0.9902 MgII-selected absorption system along the quasar PG1634+706 line of sight is "CIV-deficient", i.e. its CIV equivalent width is small relative to the kinematic spread of its MgII profile. The strong CIV absorption that is characteristic of most strong MgII absorbers is thought to arise in a corona similar to that surrounding the Milky Way disk. As such, it is of particular interest to study this CIV-deficient absorber to see if this "corona phase of gas" is absent or just weak.
We used spectra from STIS/HST, with resolution of R=30,000 and wavelength coverage from 1800{Å} to 3100{Å}, to study this MgII absorption system. In addition, our R=45,000 HIRES/Keck spectra covered MgI, MgII and FeII. A fit to the profile of this strong MgII absorber requires five blended clouds, with Doppler parameters, b, ranging from 2 to 17 km/s. Based on fits to the data from STIS/HST and HIRES/Keck of model results produced by the photoionization code CLOUDY, we reach the following conclusions: i) The metallicity is constrained to be below one tenth of the solar value, for one or more of the clouds, by the presence of a Lyman limit break; ii) MgI cannot arise in the same gas as MgII. Instead, it is possibly produced in separate, narrow clouds with b of 1 or 2 km/s; iii) A centered broad phase with b ~ 50 km/s is required to consistently fit Ly\alpha, Ly\beta, and the higher order Lyman series; iv) Both CIV and SiIV are offset from the MgII clouds, which suggests the presence of one or more additional clouds. A broad CIV component may not be required.
We acknowledge support from NSF AST 96-17185 and NASA/LTSA NAG5-6399
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The author(s) of this abstract have provided an email address for comments about the abstract: ding@astro.psu.edu