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  4. Not-so-little Red Dots: Two Massive and Dusty Starbursts at z ∼ 5-7 Pushing the Limits of Star Formation Discovered by JWST in the COSMOS-Web Survey
 
research article

Not-so-little Red Dots: Two Massive and Dusty Starbursts at z ∼ 5-7 Pushing the Limits of Star Formation Discovered by JWST in the COSMOS-Web Survey

Gentile, Fabrizio
•
Casey, Caitlin M.
•
Akins, Hollis B.
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September 1, 2024
The Astrophysical Journal Letters

We present the properties of two candidate massive (M ⋆ ∼ 1011 M ⊙) and dusty (A v > 2.5 mag) galaxies at z = 5-7 in the first 0.28 deg2 of the COSMOS-Web survey. One object is spectroscopically confirmed at z spec = 5.051, while the other has a robust z phot = 6.7 ± 0.3. Thanks to their extremely red colors (F277W-F444W ∼ 1.7 mag), these galaxies satisfy the nominal color selection for the widely studied “little red dot” (LRD) population with the exception of their spatially resolved morphologies. The morphology of our targets allows us to conclude that their red continuum is dominated by highly obscured stellar emission and not by reddened nuclear activity. Using a variety of spectral energy distribution fitting tools and star formation histories, we estimate the stellar masses to be log ( M ⋆ ) = 11.32 − 0.15 + 0.07 M ⊙ and log ( M ⋆ ) = 11.2 − 0.2 + 0.1 M ⊙ , respectively, with a red continuum emission dominated by a recent episode of star formation. We then compare their number density to the halo mass function to infer stellar baryon fractions of ϵ ⋆ ∼ 0.25 and ϵ ⋆ ∼ 0.5. Both are significantly higher than what is commonly observed in lower-z galaxies or more dust-obscured galaxies at similar redshifts. With very bright ultra-high-z Lyman-Break Galaxies and some non-AGN-dominated LRDs, such “extended” LRDs represent another population that may require very efficient star formation at early times.

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Type
research article
DOI
10.3847/2041-8213/ad738a
Scopus ID

2-s2.0-85204238142

Author(s)
Gentile, Fabrizio

Alma Mater Studiorum Università di Bologna

Casey, Caitlin M.

The University of Texas at Austin

Akins, Hollis B.

The University of Texas at Austin

Franco, Maximilien

The University of Texas at Austin

McKinney, Jed

The University of Texas at Austin

Berman, Edward

Northeastern University

Cooper, Olivia R.

The University of Texas at Austin

Drakos, Nicole E.

University of Hawaii at Hilo

Hirschmann, Michaela  

École Polytechnique Fédérale de Lausanne

Long, Arianna S.

The University of Texas at Austin

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Date Issued

2024-09-01

Published in
The Astrophysical Journal Letters
Volume

973

Issue

1

Article Number

L2

Editorial or Peer reviewed

REVIEWED

Written at

EPFL

EPFL units
GALSPEC  
FunderFunding(s)Grant NumberGrant URL

Jet Propulsion Laboratory

CNES

IF/THEN

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Available on Infoscience
January 24, 2025
Use this identifier to reference this record
https://infoscience.epfl.ch/handle/20.500.14299/243796
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