A big red dot at cosmic noon

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.

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Publication Details

Journal
Astronomy and Astrophysics
Published
2025-09-15
DOI
https://doi.org/10.1051/0004-6361/202555946
Citations
5
Primary Topic
Photocathodes and Microchannel Plates
Type
article
Field-Weighted Citation Impact
3.37
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article

A big red dot at cosmic noon

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5 citations
Astronomy and Astrophysics
Photocathodes and Microchannel Plates
3.37
article

A big red dot at cosmic noon

M. Mignoli, Colin Norman, P. Tozzi, G. Lanzuisi, F. Loiacono, Stefano Marchesi, R. Maiolino, Q. D’Amato, I. Prandoni, Giovanni Mazzolari, M. Chiaberge, Ignas Juodžbalis, Matilde Signorini, G. Zamorani, F. Calura, C. Vignali, A. Comastri, Fabio Vito, Alessandro Peca, E. Vanzella, R. Gilli, M. Brusa, Roberto Decarli, K. Iwasawa, Matteo Sapori
article en
5 citations

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.

Astronomy and AstrophysicsVol. 703
Institució Catalana de Recerca i Estudis Avançats (ES), Space Telescope Science Institute (US), Johns Hopkins University (US), University of Cambridge (GB), Arcetri Astrophysical Observatory (IT), European Space Agency (FR), Johns Hopkins University Applied Physics Laboratory (US), Yale University (US), Osservatorio astronomico di Bologna (IT), Max Planck Institute for Extraterrestrial Physics (DE), Bridge University (SS), Institut Català de Ciències del Clima (ES), Istituto di Radioastronomia di Bologna (IT), Eureka Scientific (US), Osservatorio di Astrofisica e Scienza dello Spazio, University College London (GB), Clemson University (US), University of Bologna (IT)
Openalex Percentile: Top 7%
Photocathodes and Microchannel Plates
3.37
DOIOpen Access PDFOpenAlex
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