Little Red Dots: An Abundant Population of Faint Active Galactic Nuclei at z ∼ 5 Revealed by the EIGER and FRESCO JWST Surveys

Jorryt Matthee, Rohan P. Naidu, Gabriel Brammer, John Chisholm, Anna Christina Eilers, Andy Goulding, Jenny Greene, Daichi Kashino, Ivo Labbe, Simon J. Lilly, Ruari Mackenzie, Pascal A. Oesch, Andrea Weibel, Stijn Wuyts, Mengyuan Xiao, Rongmon Bordoloi, Rychard Bouwens, Pieter van Dokkum, Garth Illingworth, Ivan KramarenkoMichael V. Maseda, Charlotte Mason, Romain A. Meyer, Erica J. Nelson, Naveen A. Reddy, Irene Shivaei, Robert A. Simcoe, Minghao Yue

Research output: Contribution to journalArticlepeer-review

20 Scopus citations


Characterizing the prevalence and properties of faint active galactic nuclei (AGNs) in the early Universe is key for understanding the formation of supermassive black holes (SMBHs) and determining their role in cosmic reionization. We perform a spectroscopic search for broad Hα emitters at z ≈ 4-6 using deep JWST/NIRCam imaging and wide field slitless spectroscopy from the EIGER and FRESCO surveys. We identify 20 Hα lines at z = 4.2-5.5 that have broad components with line widths from ∼1200-3700 km s−1, contributing ∼30%-90% of the total line flux. We interpret these broad components as being powered by accretion onto SMBHs with implied masses ∼107-8 M . In the UV luminosity range M UV,AGN+host = −21 to −18, we measure number densities of ≈10−5 cMpc−3. This is an order of magnitude higher than expected from extrapolating quasar UV luminosity functions (LFs). Yet, such AGN are found in only <1% of star-forming galaxies at z ∼ 5. The number density discrepancy is much lower when compared to the broad Hα LF. The SMBH mass function agrees with large cosmological simulations. In two objects, we detect complex Hα profiles that we tentatively interpret as caused by absorption signatures from dense gas fueling SMBH growth and outflows. We may be witnessing early AGN feedback that will clear dust-free pathways through which more massive blue quasars are seen. We uncover a strong correlation between reddening and the fraction of total galaxy luminosity arising from faint AGN. This implies that early SMBH growth is highly obscured and that faint AGN are only minor contributors to cosmic reionization.

Original languageEnglish (US)
Article number129
JournalAstrophysical Journal
Issue number2
StatePublished - Mar 1 2024

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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