Letter to the Editor

SUPER

VI. A giant molecular halo around a z∼2 quasar

¹ Institute of Theoretical Astrophysics, University of Oslo, PO Box 1029, Blindern 0315 Oslo, Norway
e-mail: claudia.cicone@astro.uio.no
² European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany
³ Department of Physics and Astronomy, University College London, London WC1E 6BT, UK
⁴ European Southern Observatory, Alonso de Cordova 3107, Casilla 19, 19001 Santiago, Chile
⁵ Centro de Astrobiología (CSIC-INTA), Ctra. de Ajalvir, Km 4, 28850 Torrejón de Ardoz, Madrid, Spain
⁶ INAF – Osservatorio Astronomico di Trieste, Via G. B. Tiepolo 11, 34143 Trieste, Italy
⁷ Scuola Normale Superiore, Piazza dei Cavalieri 7, 56126 Pisa, Italy
⁸ INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
⁹ School of Mathematics, Statistics and Physics, Newcastle University, Newcastle upon Tyne NE1 7RU, UK
¹⁰ Dipartimento di Fisica e Astronomia, Università di Firenze, Via G. Sansone 1, 50019 Sesto Fiorentino, Firenze, Italy
¹¹ INAF – Osservatorio Astronomico di Roma, Via Frascati 33, 00040 Monte Porzio Catone, Roma, Italy
¹² Centre for Extragalactic Astronomy, Durham University, South Road, Durham DH1 3LE, UK
¹³ Chalmers University of Technology, Department of Space, Earth and Environment, Onsala Space Observatory, 439 92 Onsala, Sweden
¹⁴ Dipartimento di Fisica e Astronomia, Università degli Studi di Bologna, Via P. Gobetti 93/2, 40129 Bologna, Italy
¹⁵ INAF/OAS, Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via P. Gobetti 93/3, 40129 Bologna, Italy
¹⁶ Department of Physics, University of Oxford, Denys Wilkinson Building, Keble Road, Oxford OX1 3RH, UK
¹⁷ INAF – Istituto di Astrofisica Spaziale e Fisica Cosmica di Milano, Via A. Corti 12, 20133 Milano, Italy
¹⁸ Max-Planck-Institute für Astrophysik, Karl-Schwarzschild-Strasse 1, 85748 Garching bei München, Germany

Received: 22 June 2021
Accepted: 2 September 2021

Abstract

We present the discovery of copious molecular gas in the halo of cid_346, a z = 2.2 quasar studied as part of the SINFONI survey for Unveiling the Physics and Effect of Radiative feedback (SUPER). New Atacama Compact Array (ACA) CO(3−2) observations detect a much higher flux (by a factor of 14 ± 5) than measured on kiloparsec scales (r ≲ 8 kpc) using previous snapshot Atacama Large Millimeter/submillimeter Array data. Such additional CO(3−2) emission traces a structure that extends out to r ∼ 200 kpc in projected size, as inferred through direct imaging and confirmed by an analysis of the uv visibilities. This is the most extended molecular circumgalactic medium (CGM) reservoir that has ever been mapped. It shows complex kinematics, with an overall broad line profile (FWHM = 1000 km s⁻¹) that is skewed towards redshifted velocities up to at least v ∼ 1000 km s⁻¹. Using the optically thin assumption, we estimate a strict lower limit for the total molecular CGM mass observed by ACA of M_mol^CGM > 10¹⁰ M_⊙. There is however room for up to M_mol^CGM ∼ 1.7 × 10¹² M_⊙, once optically thick CO emission with α_CO = 3.6 M_⊙ (K km s⁻¹ pc²)⁻¹ and L^′_CO(3−2)/L^′_CO(1−0) = 0.5 are assumed. Since cid_346 hosts quasar-driven ionised outflows and since there is no evidence of merging companions or an overdensity, we suggest that outflows may have played a crucial rule in seeding metal-enriched, dense gas on halo scales. However, the origin of such an extended molecular CGM remains unclear.