Witnessing the violent, merger-driven formation of an extremely massive galaxy 1.7 Gyr after the Big Bang
File(s)
Published version
Author(s)
Type
Journal Article
Abstract
We combine near-infrared imaging in two bands from the Hubble Space Telescope with archival observations of molecular gas to study SDSS J160705.16+533558.6 (J1607), an extremely luminous broad-line quasar at z = 3.65 that is also bright in the submillimeter. Via subtraction of the quasar point-spread function, we show that its host galaxy is massive, with a stellar mass of (5.8 ± 3.0) × 1011 M⊙, making it comparable to giant early-type galaxies (ETGs) at z ∼ 0. If the supermassive black hole in the quasar is accreting at the Eddington limit, then its mass is 3.5 × 109 M⊙, which is also consistent with local massive ETGs. The host has an extremely high star formation rate of 4300 ± 500 M⊙ yr−1 and a molecular gas mass of (2.4 ± 0.9) × 1010 M⊙. The quasar has two companions: one at a projected separation of 11 kpc with a stellar mass of (7.9 ± 5.0) × 1010 M⊙ but no detected molecular gas and one 6 kpc further away in the same direction with a molecular gas mass of (2.6 ± 1.3) × 1010 M⊙ but no detected stellar emission. Since neither companion shows evidence for active galactic nucleus activity, this may represent merger-driven quenching, in which the dynamics of the merger strip molecular gas from infalling galaxies. Overall, irrespective of whether the host is merging with the companions, these properties mark J1607 as forming what will become an extremely massive (∼1012 M⊙) galaxy by z = 0.
Date Issued
2025-11-13
Date Acceptance
2025-08-30
Citation
The Astrophysical Journal (ApJ), 2025, 994 (1)
ISSN
0004-637X
Publisher
IOP Publishing
Journal / Book Title
The Astrophysical Journal (ApJ)
Volume
994
Issue
1
Copyright Statement
© 2025. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
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Subjects
ACTIVE GALACTIC NUCLEI
Astronomy & Astrophysics
HOST GALAXIES
MOLECULAR GAS
Physical Sciences
QUIESCENT GALAXIES
Science & Technology
SIMILAR-TO 2
SPECTRAL ENERGY-DISTRIBUTIONS
STAR-FORMATION
SUBMILLIMETER GALAXIES
SUPERMASSIVE BLACK-HOLES
ULTRALUMINOUS INFRARED GALAXIES
Publication Status
Published
Article Number
57
Date Publish Online
2025-11-13