QSO absorption lines from QSOs

David V. Bowen, Joseph F. Hennawi, Brice Ménard, Doron Chelouche, Naohisa Inada, Masamune Oguri, Gordon T. Richards, Michael A. Strauss, Daniel E. Vanden Berk, Donald G. York

Research output: Contribution to journalArticlepeer-review


We present the results of a search for metal absorption lines in the spectra of background QSOs whose sight lines pass close to foreground QSOs. We detect Mg II λλ2796, 2803 absorption in Sloan Digital Sky Survey (SDSS) spectra of four z > 1.5 QSOs whose lines of sight pass within 26-98 h70-1 kpc of lower redshift (z ≃ 0.5-1.5) QSOs. The 100% detection rate (four out of four pairs) of Mg II in the background QSOs is clearly at odds with the incidence of associated zabs ≃ z em systems - absorbers that exist toward only a few percent of QSOs. Although the quality of our foreground QSO spectra is not as high as the SDSS data, absorption seen toward one of the background QSOs clearly does not show up at the same strength in the spectrum of the corresponding foreground QSO. This implies that the absorbing gas is distributed inhomogeneously around the QSO, presumably as a direct consequence of the anisotropic emission from the central active galactic nucleus. We discuss possible origins for the Mg II lines, including absorption by gas from the foreground QSO host galaxy, companion galaxies fueling the QSO through gravitational interactions, and tidal debris left by galaxy mergers or interactions that initiated the QSO activity. No single explanation is entirely satisfactory, and we may well be seeing a mixture of phenomena.

Original languageEnglish
Pages (from-to)L105-L108
JournalAstrophysical Journal
Issue number2 II
StatePublished - 10 Jul 2006
Externally publishedYes


  • Quasars: absorption lines
  • Quasars: general

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


Dive into the research topics of 'QSO absorption lines from QSOs'. Together they form a unique fingerprint.

Cite this