Bulge formation inside quiescent lopsided stellar disks: Connecting accretion, star formation, and morphological transformation in a z ∼ 3 galaxy group

¹ CEA, Irfu, DAp, AIM, Université Paris-Saclay, Université de Paris, CNRS, 91191 Gif-sur-Yvette, France
e-mail: boris.kalita@cea.fr
² Department of Physics & Astronomy, University of California Los Angeles, 430 Portola Plaza, Los Angeles, CA 90095, USA
³ Cosmic Dawn Center (DAWN), Denmark
⁴ Niels Bohr Institute, University of Copenhagen, Jagtvej 128, 2200 Copenhagen N, Denmark
⁵ INAF – Osservatorio Astronomico di Brera, Via Brera 28, 20121 Milano, Italy
⁶ University of Trieste, Piazzale Europa, 1, 34127 Trieste, TS, Italy
⁷ INAF – Osservatorio Astronomico di Brera, Via Brera 28, 20121 Milano, Italy
⁸ INAF – Osservatorio Astronomico di Trieste, Via Tiepolo 11, 34131 Trieste, Italy
⁹ Institut de Radioastronomie Millimétrique, 300 Rue de la Piscine, 38406 Saint-Martin d’Hères, France
¹⁰ Purple Mountain Observatory & Key Laboratory for Radio Astronomy, Chinese Academy of Sciences, 10 Yuanhua Road, Nanjing 210023, PR China

Received: 12 January 2022
Accepted: 10 June 2022

Abstract

We present well-resolved near-IR and submillimeter analysis of the three highly star-forming massive (> 10¹¹ M_⊙) galaxies within the core of the RO-1001 galaxy group at z = 2.91. Each of them displays kpc scale compact starbursting cores with properties consistent with forming galaxy bulges, embedded at the center of extended, massive stellar disks. Surprisingly, the stellar disks are unambiguously both quiescent and severely lopsided. Therefore, “outside-in” quenching is ongoing in the three group galaxies. We propose an overall scenario in which the strong mass lopsidedness in the disks (ranging from factors of 1.6 to > 3) likely generated under the effects of accreted gas and clumps, is responsible for their star-formation suppression, while funnelling gas into the nuclei and thus creating the central starbursts. The lopsided side of the disks marks the location of impact of accretion streams, with additional matter components (dust and stars) detected in their close proximity directly tracing the inflow direction. The interaction with the accreted clumps, which can be regarded as minor mergers, leads the major axes of the three galaxies to be closely aligned with the outer Lyman-α-emitting feeding filaments. These results provide the first piece of observational evidence of the impact of cold accretion streams on the formation and evolution of the galaxies they feed. In the current phase, this is taking the form of the rapid buildup of bulges under the effects of accretion, while still preserving massive quiescent and lopsided stellar disks at least until encountering a violent major merger.