Possible environmental quenching in an interacting little red dot pair at z ∼ 7

¹ Institute for Computational Astrophysics and Department of Astronomy and Physics, Saint Mary’s University, 923 Robie Street, Halifax, NS B3H 3C3, Canada
² Observatorio Astronómico de Córdoba, Universidad Nacional de Córdoba, Laprida 854, X5000 Córdoba, Argentina
³ Department of Astronomy, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
⁴ Kapteyn Astronomical Institute, University of Groningen, P.O. Box 800, 9700AV Groningen, The Netherlands
⁵ Faculty of Mathematics and Physics, Jadranska ulica 19, SI-1000 Ljubljana, Slovenia
⁶ David A. Dunlap Department of Astronomy and Astrophysics, University of Toronto, 50 St. George Street, Toronto, Ontario M5S 3H4, Canada
⁷ INAF – Osservatorio Astronomico di Roma, Via Frascati 33, Monte Porzio Catone 00078, Italy
⁸ National Research Council of Canada, Herzberg Astronomy & Astrophysics Research Centre, 5071 West Saanich Road, Victoria, BC V9E 2E7, Canada
⁹ Department of Physics and Astronomy, University of California Davis, 1 Shields Avenue, Davis, CA 95616, USA
¹⁰ Cosmic Dawn Center (DAWN), Copenhagen, Denmark
¹¹ Niels Bohr Institute, University of Copenhagen, Jagtvej 128, DK-2200 Copenhagen N, Denmark
¹² Columbia Astrophysics Laboratory, Columbia University, 550 West 120th Street, New York, NY 10027, USA
¹³ Department of Physics and Astronomy, York University, 4700 Keele St. Toronto, Ontario M3J 1P3, Canada
¹⁴ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, Maryland 21218, USA

^⋆ Corresponding author: Rosa.MeridaGonzalez@smu.ca

Received: 28 January 2025
Accepted: 14 May 2025

Abstract

We report the discovery of a z ∼ 7 group of galaxies that contains two little red dots (LRDs) just 3.3 kpc apart, along with three potential satellite galaxies, as part of the Canadian NIRISS Unbiased Cluster Survey (CANUCS). The spectral energy distributions (SEDs) of this LRD pair show evidence of a Balmer break, consistent with a recent (∼100 Myr) quenching of star formation. In contrast, the satellites are compatible with a recent-onset (∼100 Myr), ongoing burst of star formation. LRD1’s SED is consistent with a dust-free active galactic nucleus (AGN) being the source of the UV excess in the galaxy. The optical continuum would be powered by the emission from an obscured post-starburst and the AGN at a subdominant level. LRD2’s SED is more ambiguous, but it could also be indicative of a dust-free AGN. In this scenario, these LRDs would be massive (M_⋆ ∼ 10¹⁰ M_⊙) and dusty (A(V) >  1 mag) and the three satellites would be lower-mass objects (M_⋆ ∼ 10^8 − 9 M_⊙) subject to low dust attenuations. The proximity of the two LRDs suggests that their interaction is responsible for their recent star formation histories, which can be interpreted as environmental bursting and quenching in the epoch of reionization.