RUBIES: Evolved Stellar Populations with Extended Formation Histories at z ∼ 7–8 in Candidate Massive Galaxies Identified with JWST/NIRSpec

Bingjie Wang; Joel Leja; Anna de Graaff; Gabriel B. Brammer; Andrea Weibel; Pieter van Dokkum; Josephine F. W. Baggen; Katherine A. Suess; Jenny E. Greene; Rachel Bezanson; Nikko J. Cleri; Michaela Hirschmann; Ivo Labbé; Jorryt Matthee; Ian McConachie; Rohan P. Naidu; Erica Nelson; Pascal A. Oesch; David J. Setton; Christina C. Williams

doi:10.3847/2041-8213/ad55f7

The Astrophysical Journal Letters (Jan 2024)

RUBIES: Evolved Stellar Populations with Extended Formation Histories at z ∼ 7–8 in Candidate Massive Galaxies Identified with JWST/NIRSpec

Bingjie Wang,
Joel Leja,
Anna de Graaff,
Gabriel B. Brammer,
Andrea Weibel,
Pieter van Dokkum,
Josephine F. W. Baggen,
Katherine A. Suess,
Jenny E. Greene,
Rachel Bezanson,
Nikko J. Cleri,
Michaela Hirschmann,
Ivo Labbé,
Jorryt Matthee,
Ian McConachie,
Rohan P. Naidu,
Erica Nelson,
Pascal A. Oesch,
David J. Setton,
Christina C. Williams

Affiliations

Bingjie Wang: ORCiD; Department of Astronomy & Astrophysics, The Pennsylvania State University , University Park, PA 16802, USA ; [email protected]; Institute for Computational & Data Sciences, The Pennsylvania State University , University Park, PA 16802, USA; Institute for Gravitation and the Cosmos, The Pennsylvania State University , University Park, PA 16802, USA
Joel Leja: ORCiD; Department of Astronomy & Astrophysics, The Pennsylvania State University , University Park, PA 16802, USA ; [email protected]; Institute for Computational & Data Sciences, The Pennsylvania State University , University Park, PA 16802, USA; Institute for Gravitation and the Cosmos, The Pennsylvania State University , University Park, PA 16802, USA
Anna de Graaff: ORCiD; Max-Planck-Institut für Astronomie , Königstuhl 17, D-69117, Heidelberg, Germany
Gabriel B. Brammer: ORCiD; Cosmic Dawn Center (DAWN) , Copenhagen, Denmark; Niels Bohr Institute, University of Copenhagen , Jagtvej 128, Copenhagen, Denmark
Andrea Weibel: ORCiD; Department of Astronomy, University of Geneva , Chemin Pegasi 51, 1290 Versoix, Switzerland
Pieter van Dokkum: ORCiD; Department of Astronomy, Yale University , New Haven, CT 06511, USA
Josephine F. W. Baggen: ORCiD; Department of Astronomy, Yale University , New Haven, CT 06511, USA
Katherine A. Suess: ORCiD; Kavli Institute for Particle Astrophysics and Cosmology and Department of Physics, Stanford University , Stanford, CA 94305, USA
Jenny E. Greene: ORCiD; Department of Astrophysical Sciences, Princeton University , Princeton, NJ 08544, USA
Rachel Bezanson: ORCiD; Department of Physics & Astronomy and PITT PACC, University of Pittsburgh , Pittsburgh, PA 15260, USA
Nikko J. Cleri: ORCiD; Department of Physics and Astronomy, Texas A&M University , College Station, TX 77843-4242, USA; George P. and Cynthia Woods Mitchell Institute for Fundamental Physics and Astronomy, Texas A&M University , College Station, TX 77843-4242, USA
Michaela Hirschmann: ORCiD; Institute of Physics , Lab for Galaxy Evolution, EPFL, Observatoire de Sauverny, Chemin Pegasi 51, 1290 Versoix, Switzerland
Ivo Labbé: ORCiD; Centre for Astrophysics and Supercomputing, Swinburne University of Technology , Melbourne, VIC 3122, Australia
Jorryt Matthee: ORCiD; Institute of Science and Technology Austria (ISTA) , Am Campus 1, 3400 Klosterneuburg, Austria
Ian McConachie: ORCiD; Department of Physics and Astronomy, University of California , Riverside, Riverside, CA 92521, USA
Rohan P. Naidu: ORCiD; MIT Kavli Institute for Astrophysics and Space Research , Cambridge, MA 02139, USA
Erica Nelson: ORCiD; Department for Astrophysical and Planetary Science, University of Colorado , Boulder, CO 80309, USA
Pascal A. Oesch: ORCiD; Cosmic Dawn Center (DAWN) , Copenhagen, Denmark; Department of Astronomy, University of Geneva , Chemin Pegasi 51, 1290 Versoix, Switzerland
David J. Setton: ORCiD; Department of Astrophysical Sciences, Princeton University , Princeton, NJ 08544, USA
Christina C. Williams: ORCiD; NSF’s National Optical-Infrared Astronomy Research Laboratory , Tucson, AZ 85719, USA; Steward Observatory, University of Arizona , Tucson, AZ 85721, USA

DOI: https://doi.org/10.3847/2041-8213/ad55f7
Journal volume & issue: Vol. 969, no. 1
p. L13

Abstract

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The identification of red, apparently massive galaxies at z > 7 in early James Webb Space Telescope (JWST) photometry suggests a strongly accelerated time line compared to standard models of galaxy growth. A major uncertainty in the interpretation is whether the red colors are caused by evolved stellar populations, dust, or other effects such as emission lines or active galactic nuclei (AGNs). Here we show that three of the massive galaxy candidates at z = 6.7–8.4 have prominent Balmer breaks in JWST/NIRSpec spectroscopy from the RUBIES program. The Balmer breaks demonstrate unambiguously that stellar emission dominates at λ _rest = 0.4 μ m and require formation histories extending hundreds of millions of years into the past in galaxies only 600–800 Myr after the big bang. Two of the three galaxies also show broad Balmer lines, with H β FWHM > 2500 km s ^−1 , suggesting that dust-reddened AGNs contribute to, or even dominate, the spectral energy distributions of these galaxies at λ _rest ≳ 0.6 μ m. All three galaxies have relatively narrow [O iii ] lines, seemingly ruling out a high-mass interpretation if the lines arise in dynamically relaxed, inclined disks. Yet the inferred masses also remain highly uncertain. We model the high-quality spectra using Prospector to decompose the continuum into stellar and AGN components and explore limiting cases in stellar/AGN contribution. This produces a wide range of possible stellar masses, spanning M _⋆ ∼ 10 ^9 −10 ^11 M _⊙ . Nevertheless, all fits suggest a very early and rapid formation, most of which follow with a truncation in star formation. Potential origins and evolutionary tracks for these objects are discussed, from the cores of massive galaxies to low-mass galaxies with overmassive black holes. Intriguingly, we find all of these explanations to be incomplete; deeper and redder data are needed to understand the physics of these systems.

Published in The Astrophysical Journal Letters

ISSN: 2041-8205 (Print); 2041-8213 (Online)
Publisher: IOP Publishing
Country of publisher: United Kingdom
LCC subjects: Science: Astronomy: Astrophysics
Website: https://iopscience.iop.org/journal/2041-8205

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