GA-NIFS: Dissecting the multiple sub-structures and probing their complex interactions in the Lyα emitter galaxy CR7 at z = 6.6 with JWST/NIRSpec

¹ Dipartimento di Fisica e Astronomia, Università degli Studi di Firenze, Via G. Sansone 1, I-50019, Sesto Fiorentino, Firenze, Italy
² INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125, Firenze, Italy
³ Kavli Institute for Cosmology, University of Cambridge, Madingley Road, Cambridge CB3 0HE, UK
⁴ Cavendish Laboratory, University of Cambridge, 19 J. J. Thomson Ave., Cambridge CB3 0HE, UK
⁵ Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
⁶ Centro de Astrobiología (CAB), CSIC-INTA, Ctra. de Ajalvir km 4, Torrejón de Ardoz, E-28850, Madrid, Spain
⁷ University of Oxford, Department of Physics, Denys Wilkinson Building, Keble Road, Oxford OX13RH, UK
⁸ Scuola Normale Superiore, Piazza dei Cavalieri 7, I-56126 Pisa, Italy
⁹ Sorbonne Université, CNRS, UMR 7095, Institut d’Astrophysique de Paris, 98 bis bd Arago, 75014 Paris, France
¹⁰ Max-Planck-Institut für extraterrestrische Physik (MPE), Gießenbachstraße 1, 85748 Garching, Germany
¹¹ NRC Herzberg, 5071 West Saanich Rd, Victoria, BC V9E 2E7, Canada
¹² European Space Agency, c/o STScI, 3700 San Martin Drive, Baltimore, MD 21218, USA
¹³ European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany

^⋆ Corresponding author: cosimo.marconcini@unifi.it

Received: 14 November 2024
Accepted: 23 May 2025

Abstract

We present JWST/NIRSpec integral field spectroscopic (IFS) observations of the Lyα emitter CR7 at z ∼ 6.6, observed as part of the GA-NIFS program. Using low-resolution PRISM (R ∼ 100) data, we confirm the observation of a bright Lyα emitter with a diffuse Lyα halo extending up to 3 kpc from the peak of ionised emission. Both features are associated with the most massive UV bright galaxy in the system, CR7-A. We confirm the presence of two additional UV-bright satellites (CR7-B and CR7-C) detected at projected distances of 6.4 and 5.2 kpc from the primary source. We performed a spectral energy distribution fitting of the low-resolution data, and it revealed an inverted star formation history between two satellites at early epochs and a spatially resolved anti-correlation of the gas-phase metallicity and the star formation rate density, likely driven by the gas exchange among the satellites and favouring the merger scenario for CR7. From the high-resolution G395H (R ∼ 2700) data, we discovered at least one additional companion mainly traced by the [O III]λ5007 emission line, although it is not detected in continuum emission. We disentangled the kinematics of the system and reveal extended ionised emission linking the main galaxy and the satellite. We spatially resolved the [O III]λ5007, [O III]4363, and Hγ emission lines and used a diagnostic diagram tailored to high-z systems to reveal tentative evidence of active galactic nucleus ionisation across the main galaxy (CR7-A) and the N-E companion (CR7-B). Moreover, we detected an unresolved blueshifted outflow from one of the satellites and present first evidence for a redshifted outflow from the main galaxy. Finally, we computed the resolved electron temperature (T_e∼1.6×10⁴ K) and metallicity maps (log(Z/Z_⊙) from –0.8 to –0.5), and we provide insights on how the physical properties of the system evolved at earlier epochs.