Cosmic Duets

I. High-spatial resolution spectroscopy of dual and lensed active galactic nuclei with MUSE-NFM

¹ University of Trento, Via Sommarive 14, I-38123, Trento, Italy
² Università di Firenze, Dipartimento di Fisica e Astronomia, Via G. Sansone 1, 50019, Sesto F.no, Firenze, Italy
³ INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125, Firenze, Italy
⁴ Centro de Astrobiología (CAB), CSIC–INTA, Ctra. de Ajalvir Km 4, 28850, Torrejón de Ardoz, Madrid, Spain
⁵ Università degli Studi di Milano-Bicocca, Piazza della Scienza 3, 20126, Milano, Italy
⁶ INAF – Osservatorio Astronomico di Trieste, Via G.B. Tiepolo 11, I-34143, Trieste, Italy
⁷ Dipartimento di Fisica e Scienze della Terra, Università di Ferrara, Via G. Saragat 21, 44122, Ferrara, Italy
⁸ INAF – Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Gobetti 93/3, I-40129, Bologna, Italy
⁹ Max Planck Institute for Extraterrestrial Physics, Giessenbachstraße 1, 85748, Garching, Germany
¹⁰ Dipartimento di Matematica e Fisica, Università degli Studi Roma Tre, Via della Vasca Navale 84, 00146, Roma, Italia
¹¹ Scuola Normale Superiore, Piazza dei Cavalieri 7, 56126, Pisa, Italy
¹² Indian Institute Of Astrophysics, 100 Feet Rd, Santhosapuram, 2nd Block, Koramangala, Bengaluru, Karnataka, 560034, India
¹³ Institute of Theoretical Astrophysics, University of Oslo, P.O Box 1029, Blindern, 0315, Oslo, Norway
¹⁴ Department of Physics and Astronomy, University of California Los Angeles, 430 Portola Plaza, Los Angeles, CA, 90095, USA
¹⁵ INAF – Istituto di Astrofisica e Planetologia Spaziali, Via Fosso del Cavaliere 100, 00133, Rome, Italy
¹⁶ Dipartimento di Fisica, Università di Roma Tor Vergata, Via della Ricerca Scientifica, I-00133, Roma, Italy
¹⁷ INAF – Osservatorio Astronomico di Brera, Via Brera 28, 20121, Milano, Italy
¹⁸ INAF – Istituto di Radioastronomia, Via Piero Gobetti 101, 40129, Bologna, Italy
¹⁹ Physics and Astronomy Department “Augusto Righi”, Università di Bologna, Via Gobetti 93/2, 40129, Bologna, Italy
²⁰ Institut d’Astrophysique de Paris, 98bis Bd Arago, 75014, Paris, France

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Received: 12 December 2025
Accepted: 5 April 2026

Abstract

We present the first-year results of the MUSE Large Program “Cosmic Duets”, whose goal is to obtain adaptive-optics assisted MUSE observations with a typical angular resolution of 0.1″ − 0.2″ in order to provide integral-field spectroscopy of sub-arcsec separation dual and lensed active galactic nucleus (AGN) candidates. These observations reveal previously unexplored properties of dual and lensed systems that are key to understanding galaxy evolution, supermassive black hole mergers, and strong-lensing modeling. Targets were efficiently selected using the Gaia multipeak (GMP) technique, which identifies pairs of point-like sources with angular separations below 0.8″ in the Gaia catalog. MUSE spatially resolved spectroscopy provides accurate redshifts, ionization diagnostics, and identification of absorption systems along the line of sight. We report results for 30 GMP-selected targets at z = 0.5 − 3.5. All systems show at least two spatially resolved components. Nineteen objects are confirmed as AGN multiplets, including six dual AGN, ten doubly lensed quasars, and three quadruply lensed systems, while the remaining 11 correspond to chance alignments with foreground stars. Among all the spectroscopically confirmed dual AGN in the literature, 27 pairs have projected separations below 7 kpc in this redshift regime, and our sample accounts for 22% of the total. We studied dual and lensed AGN distributions as a function of redshift, magnitude, and projected separation while accounting for selection effects, and we find that bright systems (J ≲ 16.5) are dominated by lensed quasars, whereas the relative fraction of dual AGN increases at fainter magnitudes. This first-year sample demonstrates the high efficiency of GMP preselection combined with MUSE spectroscopy for identifying sub-arcsec dual and lensed AGN. The full program, targeting ∼150 systems, will enable statistical studies of dual AGN incidence as a function of redshift, separation, and luminosity and allow for precise characterization of the mass composition and distribution in strong lensing galaxies.