The detection of the lambda 2175 A feature, and further analysis of the BAL line profile structure in the gravitational lens candidate UM425

摘要

We obtained MMT spectra of the gravitational lens candidate UM425 to comparethe redshifts and line profile structures of lens components A and B, which areseparated by ~6.5". The CIV lambda 1550 A emission in both A and B exhibitsBroad Absorption Line (BAL) structure, consistent with the earlier detection ofBAL structure in OVI lambda 1033 A and NV lambda 1240 A that was found with theInternational Ultraviolet Explorer (IUE) in component A. Cross-correlation ofthe spectra of A and B using emission lines of CIV lambda 1550 A, HeII lambda1640 A, NIII lambda 1750 A, CIII] lambda 1909 A and MgII lambda 2800 A revealsa difference in the redshifts of A & B. However, the detailed BAL line profilestructure found in spectra of A & B are strikingly similar to one another,which suggests the system is lensed. The spectra of A & B also indicatesignificant dust extinction, which we base on the presence of the lambda 2175 Aabsorption feature in the rest frame of the QSO (z_{QSO}=1.47). This feature iscommonly seen in galactic sources, but is not generally observed in QSOspectra. Our spectra show the presence of the lambda 2175 A absorption featurein spectra of both images associated with the gravitational lens UM425. Basedupon the strong similarity of BAL line profile structure exhibited by UM425A&B,particularly the presence of the lambda 2175 dust absorption feature in spectraof both images, we conclude that UM425 is a gravitational lens.