Strong Rest-UV Emission Lines in a “Little Red Dot” Active Galactic Nucleus at z = 7: Early Supermassive Black Hole Growth alongside Compact Massive Star Formation?

Hollis B. Akins; Caitlin M. Casey; Danielle A. Berg; John Chisholm; Aidan P. Cloonan; Maximilien Franco; Steven L. Finkelstein; Seiji Fujimoto; Anton M. Koekemoer; Vasily Kokorev; Erini Lambrides; Brant E. Robertson; Anthony J. Taylor; David A. Coulter; Ori Fox; Mitchell Karmen

doi:10.3847/2041-8213/adab76

The Astrophysical Journal Letters (Jan 2025)

Strong Rest-UV Emission Lines in a “Little Red Dot” Active Galactic Nucleus at z = 7: Early Supermassive Black Hole Growth alongside Compact Massive Star Formation?

Hollis B. Akins,
Caitlin M. Casey,
Danielle A. Berg,
John Chisholm,
Aidan P. Cloonan,
Maximilien Franco,
Steven L. Finkelstein,
Seiji Fujimoto,
Anton M. Koekemoer,
Vasily Kokorev,
Erini Lambrides,
Brant E. Robertson,
Anthony J. Taylor,
David A. Coulter,
Ori Fox,
Mitchell Karmen

Affiliations

Hollis B. Akins: ORCiD; Department of Astronomy, The University of Texas at Austin , 2515 Speedway Blvd. Stop C1400, Austin, TX 78712, USA ; [email protected]
Caitlin M. Casey: ORCiD; Department of Physics, University of California , Santa Barbara, CA 93106-9530, USA; Cosmic Dawn Center (DAWN), Denmark
Danielle A. Berg: ORCiD; Department of Astronomy, The University of Texas at Austin , 2515 Speedway Blvd. Stop C1400, Austin, TX 78712, USA ; [email protected]
John Chisholm: ORCiD; Department of Astronomy, The University of Texas at Austin , 2515 Speedway Blvd. Stop C1400, Austin, TX 78712, USA ; [email protected]
Aidan P. Cloonan: ORCiD; Department of Astronomy, University of Massachusetts Amherst , Amherst, MA 01003, USA
Maximilien Franco: ORCiD; Department of Astronomy, The University of Texas at Austin , 2515 Speedway Blvd. Stop C1400, Austin, TX 78712, USA ; [email protected]
Steven L. Finkelstein: ORCiD; Department of Astronomy, The University of Texas at Austin , 2515 Speedway Blvd. Stop C1400, Austin, TX 78712, USA ; [email protected]
Seiji Fujimoto: ORCiD; Department of Astronomy, The University of Texas at Austin , 2515 Speedway Blvd. Stop C1400, Austin, TX 78712, USA ; [email protected]
Anton M. Koekemoer: ORCiD; Space Telescope Science Institute , 3700 San Martin Dr., Baltimore, MD 21218, USA
Vasily Kokorev: ORCiD; Department of Astronomy, The University of Texas at Austin , 2515 Speedway Blvd. Stop C1400, Austin, TX 78712, USA ; [email protected]
Erini Lambrides: ORCiD; NASA Goddard Space Flight Center , 8800 Greenbelt Rd., Greenbelt, MD 20771, USA
Brant E. Robertson: ORCiD; Department of Astronomy and Astrophysics, University of California , Santa Cruz, 1156 High St., Santa Cruz, CA 95064, USA
Anthony J. Taylor: ORCiD; Department of Astronomy, The University of Texas at Austin , 2515 Speedway Blvd. Stop C1400, Austin, TX 78712, USA ; [email protected]
David A. Coulter: ORCiD; Space Telescope Science Institute , Baltimore, MD 21218, USA
Ori Fox: ORCiD; Space Telescope Science Institute , Baltimore, MD 21218, USA
Mitchell Karmen: ORCiD; Physics and Astronomy Department, Johns Hopkins University , Baltimore, MD 21218, USA

DOI: https://doi.org/10.3847/2041-8213/adab76
Journal volume & issue: Vol. 980, no. 2
p. L29

Abstract

Read online

JWST has now revealed a population of broad-line active galactic nuclei (AGN) at z ≳ 4 characterized by a distinctive spectral energy distribution shape, with a very red rest-frame optical and very blue rest-frame UV continuum. While the optical continuum is thought to originate from the accretion disk, the origin of the UV continuum has been largely unclear. We report the detection of the strong rest-frame UV emission lines of C iii ] λλ 1907, 1909 and C iv λλ 1549, 1551 in a “little red dot” AGN, COS-66964. Spectroscopically confirmed at z = 7.0371, COS-66964 exhibits broad H α emission (FWHM ∼ 2000 km s ^−1 ) and weak broad H β , implying significant dust attenuation to the broad-line region ( ${A}_{V}=3.{9}_{-0.9}^{+1.7}$ ). The H α line width implies a central supermassive black hole (SMBH) mass of ${M}_{{\rm{BH}}}=\left(1.{9}_{-0.7}^{+1.6}\right)\times 1{0}^{7}$ M _⊙ and an Eddington ratio λ ∼ 0.3–0.5. While marginal He ii λ 4687 and [Fe x ] λ 6376 detections further indicate that the AGN dominates in the rest-frame optical, the nondetection of He ii λ 1640 in the UV despite high EW C iii ] and C iv (∼35 Å) is more consistent with photoionization by massive stars. The nondetection of Mg ii λλ 2800 is similarly inconsistent with an AGN scattered light interpretation. Assuming the rest-frame UV is dominated by stellar light, we derive a stellar mass of $\mathrm{log}{M}_{\star }/{M}_{\odot }\sim 8.5$ , implying an elevated M _BH / M _⋆ ratio ∼2 orders of magnitude above the local relation, but consistent with other high- z AGN discovered by JWST. The source is unresolved in all bands, implying a very compact size ≲200 pc in the UV. This suggests that the simultaneous buildup of compact stellar populations (i.e., galaxy bulges) and the central SMBH is ongoing even at z ≳ 7.

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

About the journal

Abstract

Keywords