The Detection of the λ2175 Feature and Further Analysis of the Broad Absorption Line Profile Structure in the Gravitational Lens Candidate UM 425

Abstract

We obtained Multiple Mirror Telescope spectra of the gravitational lens candidate UM 425 to compare the redshifts and line profile structures of lens components A and B, which are separated by approximately 65. The C IV λ1550 emission in both A and B exhibits broad absorption line (BAL) structure, consistent with the earlier detection of BAL structure in O VI λ1033 and N V λ1240 that was found with the International Ultraviolet Explorer in component A. Cross-correlation of the spectra of A and B using emission lines of C IV λ1550, He II λ1640, N III λ1750, C III] λ1909, and Mg II λ2800 reveals a difference in the redshifts of A and B. However, the detailed BAL profile structure found in the spectra of A and B are strikingly similar to one another, which suggests the system is lensed. The spectra of A and B also indicate significant dust extinction, which we base on the presence of the λ2175 absorption feature in the rest frame of the QSO (zQSO=1.47). This feature is commonly seen in galactic sources but is not generally observed in QSO spectra. Our spectra show the presence of the λ2175 absorption feature in spectra of both images associated with the gravitational lens UM 425. Based upon the strong similarity of BAL profile structure exhibited by UM 425A and UM 425B, particularly the presence of the λ2175 dust absorption feature in spectra of both images, we conclude that UM 425 is a gravitational lens.