A big red dot at cosmic noon
Year: 2025
Type: article
Abstract: We report the discovery of a little red dot (LRD), dubbed BiRD (‘big red dot’), at z ∼ 2.33 in the field around the z ∼ 6.3 quasar SDSS J1030+0524. Using JWST/NIRCam images, we identified it as a bright outlier in the F 200 W − F 356 W color versus F 356 W magnitude diagram of point sources in the field. The NIRCam/WFSS spectrum reveals the emission from He I λ 10830 and Pa γ line, both displaying a narrow and a broad ( FWHM ≳ 2000 km s −1 ) component. The He I line is affected by an absorption feature, tracing dense gas with He I column density in the 2 3 S level N (He I ) ∼ 0.5 − 1.2 × 10 14 cm −2 , depending on the location of the absorber, which is outflowing at a speed of Δ v = −830 −148 +131 km s −1 . As observed in the majority of LRDs, BiRD does not exhibit any X-ray or radio emission down to 3.7 × 10 42 erg s −1 and 3 × 10 39 erg s −1 , respectively. The black hole mass and the bolometric luminosity, both inferred from the Pa γ broad component, amount to M BH ∼ 10 8 M ⊙ and L bol ∼ 3 × 10 45 erg s −1 , respectively. Intriguingly, BiRD presents strict analogies with other two LRDs spectroscopically confirmed at cosmic noon, namely, GN-28074 (nicknamed Rosetta Stone) at z ∼ 2.26 and RUBIES-BLAGN-1 at z ∼ 3.1. The blueshifted He I absorption detected for all three sources suggests that gas outflows could be common in LRDs. We derived a first estimate of the space density of LRDs at z ∼ 2 − 3 based on JWST data, as a function of the bolometric luminosity and black hole mass. The space density Φ( L ) = 4.0 −2.4 +4.0 × 10 −6 Mpc −3 dex −1 is only a factor of ∼2 − 3 lower than that of UV-selected quasars with comparable bolometric luminosity and redshift, meaning that the contribution of LRDs to the broader AGN population is also relevant at cosmic noon. A similar trend has also been observed with respect to black hole masses. As suggested by recent theories, if LRDs can indeed serves as probes of the very first and rapid growth of black hole seeds, our finding suggests that the formation of black hole seeds continues to be efficient at least up to cosmic noon.
Source: Astronomy and Astrophysics
Authors: Federica Loiacono, Roberto Gilli, Marco Mignoli, Giovanni Mazzolari, Roberto Decarli, Marcella Brusa, Francesco Calura, Marco Chiaberge, Andrea Comastri, Quirino D’Amato, Kazushi Iwasawa, Ignas Juodžbalis, Giorgio Lanzuisi, Roberto Maiolino, Stefano Marchesi, Colin Norman, Alessandro Peca, Isabella Prandoni, Matteo Sapori, Matilde Signorini, Paolo Tozzi, Eros Vanzella, Cristian Vignali, Fabio Vito, Gianni Zamorani
Institutions: Osservatorio di Astrofisica e Scienza dello Spazio, National Institute for Astrophysics, Max Planck Institute for Extraterrestrial Physics, University of Bologna, Johns Hopkins University, European Space Agency, Arcetri Astrophysical Observatory, Institució Catalana de Recerca i Estudis Avançats, Institut de Ciències del Cosmos, Universitat de Barcelona, University of Cambridge, University College London, Clemson University, Space Telescope Science Institute, Yale University, Eureka Scientific, Istituto di Radioastronomia di Bologna
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $1,865
Funders: National Aeronautics and Space Administration, Space Telescope Science Institute, UK Research and Innovation, Royal Society, Ministero dell’Istruzione, dell’Università e della Ricerca, Istituto Nazionale di Astrofisica, Huo Family Foundation, Science and Technology Facilities Council, Agencia Estatal de Investigación
OpenAlex ID: W4414196103