Previous abstract Next abstract
Session 98 - AGN-Absorption/Emission.
Display session, Thursday, January 16
The bright (V\sim 16.5) quasar SBS1542+541 is remarkable for its combination of high redshift (z=2.361), the presence of broad absorption lines, and an unusual paucity of intervening Lyman-limit absorption systems along the line of sight. In fact, only one Lyman-limit system is positively identified, leaving the flux largely unattenuated down to below 1200 ÅThis offers a unique opportunity to study broad absorption lines in the far UV, down through \sim 400 Å\ in the rest frame. We have analyzed the spectrum of SBS1542+541 using HST FOS data in the UV (\sim 400-950 Å\ rest frame) and MMT data in the visible (\sim 950-2300 Å\ rest frame). We find the broad absorption system to be completely lacking in low-ionization species, but showing strong contributions from high-ionization species such as O\,\sc vi, Ne\,\sc viii, and even Mg\,\sc x, which has a creation ionization potential in excess of 300 eV. Absorption by H\,\sc i, C\,\sc iv, and N\,\sc v, generally reported to be quite strong in BAL objects, is very modest in SBS1542+541, indicating that the vast majority of these atoms are ionized to higher stages. The existence of only high-ionization lines suggests that it may be possible to describe the broad absorption line system by a single-zone photoionization model with an exceptionally high ionization parameter.
Program listing for Thursday