Quasi-Stellar Objects acting as Strong Gravitational Lenses in the SDSS-III BOSS survey

Abstract

We present a sample of \(12\) Quasi-Stellar Objects (QSOs) potentially acting as strong gravitational lenses on background Emission Line Galaxies (ELGs) or Lyman-\(\alpha\) Emitters (LAEs). The candidates are selected through a systematic search of the \(350793\) QSOs spectra in the Sloan Digital Sky Survey (SDSS)-III Data Release 12 (DR12) within the Baryon Oscillation Spectroscopic Survey (BOSS). Candidates are identified by looking for compound spectra, where additional emission lines cannot be associated with the spectral features of the QSOs. The narrow diameter of BOSS fibers (2") ensures that the object responsible for the additional emission lines must lie close to the line of sight of the QSO. We focus our search on additional objects securely identified at higher redshifts than the QSOs.Among the 12 candidates identified, \(9\) have definite evidence for the presence of a background ELG identified by at least \(4\) higher-redshift emission lines. The remaining \(3\) probable candidates present a strong asymmetrical emission line attributed to a higher-redshift LAE. The QSO-Galaxy lens candidates have QSO redshifts in the range \(0.24\lesssim z_{\rm{QSO}} \lesssim 0.66\) and background galaxy redshifts in the range \(0.48 \lesssim z_s \lesssim 0.94\) whereas the QSO-LAE lens candidates have QSO redshifts in the range \(0.75 \lesssim z_{\rm{QSO}} \lesssim 1.23\) and source LAE redshifts in the range \(2.17 \lesssim z_s \lesssim 4.48\). Upon confirmation of the lensing nature of the systems, this sample may quadruple the number of known QSOs acting as strong lenses. Future imaging of the full sample will allow to model the radial mass profile of QSO host galaxies and study the scaling relations between Super-Massive Black Holes (SMBHs) and their host galaxies.