J1721+8842: A gravitationally lensed binary quasar with a proximate damped Lyman- α absorber
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High-redshift binary quasars provide key insights into mergers and quasar activity, and are useful tools for probing the spatial kinematics and chemistry of galaxies along the line of sight. However, only three sub-10-kpc binaries have been confirmed above z = 1. Gravitational lensing would provide a way to easily resolve such binaries, study them in higher resolution, and provide more sightlines, though the required alignment with a massive foreground galaxy is rare. Through image deconvolution of StanCam Nordic Optical Telescope (NOT) monitoring data, we reveal two further point sources in the known, z ≈ 2.38, quadruply lensed quasar (quad) J1721+8842. An ALFOSC/NOT long-slit spectrum shows that the brighter of these two sources is a quasar with z = 2.369 ± 0.007 based on the C » III] line, while the C » III] redshift of the quad is z = 2.364 ± 0.003. Lens modelling using point-source positions rules out a single source model, favouring an isothermal lens mass profile with two quasar sources separated by ∼6.0 kpc (0.73″) in projection. Given the resolving ability from lensing and current lensed quasar statistics, this discovery suggests a large population of undiscovered, unlensed sub-10-kpc binaries. We also analyse spectra of two images of the quad, showing narrow Lyα emission within the trough of a proximate damped Lyman-α absorber (PDLA). An apparent mismatch between the continuum and narrow line flux ratios provides a new potential tool for simultaneously studying microlensing and the quasar host galaxy. Signs of the PDLA are also seen in the second source, but a deeper spectrum is still required to confirm this. Thanks to the multiple lines of sight from lensing and two quasar sources, this system offers simultaneous subparsec- and kiloparsec-scale probes of a PDLA.
| Originalsprog | Engelsk |
|---|---|
| Artikelnummer | A113 |
| Tidsskrift | Astronomy and Astrophysics |
| Vol/bind | 657 |
| Antal sider | 10 |
| ISSN | 0004-6361 |
| DOI | |
| Status | Udgivet - 1 jan. 2022 |
Bibliografisk note
Funding Information:
Programme (FP7/2013-2016) under grant agreement No. 312430 (OPTICON). This work is based on observations made with the Nordic Optical Telescope, owned in collaboration by the University of Turku and Aarhus University, and operated jointly by Aarhus University, the University of Turku and the University of Oslo, representing Denmark, Finland and Norway, the University of Iceland and Stockholm University at the Observatorio del Roque de los Muchachos, La Palma, Spain, of the Instituto de Astrofisica de Canarias. Further data were obtained through an Agreement between Aarhus University and the Ecole Polytechnique Fédérale de Lausanne (EPFL), as part of the High-cadence Lens Monitoring for Time Delay Cosmography Program. The data presented here were obtained [in part] with ALFOSC, which is provided by the Instituto de Astrofisica de Andalucia (IAA) under a joint agreement with the University of Copenhagen and NOT.
Funding Information:
Acknowledgements. We would like to thank Aymeric Galan and Giorgos Vernardos for helpful discussions. This work is supported by the Swiss National Science Foundation (SNSF) and by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (COSMI-CLENS: grant agreement No 787886). AA’s work is funded by Villum Experiment Grant Cosmic Beacons (project number 36225). The research leading to these results has received funding from the European Union Seventh Framework
Funding Information:
This work is supported by the Swiss National Science Foundation (SNSF) and by the European Research Council (ERC) under the European Union?s Horizon 2020 research and innovation program (COSMICLENS: grant agreement No 787886). AA?s work is funded by Villum Experiment Grant Cosmic Beacons (project number 36225). The research leading to these results has received funding from the European Union Seventh Framework Programme (FP7/2013-2016) under grant agreement No. 312430 (OPTICON).
Publisher Copyright:
© ESO 2022.
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