Investigating the growth of little red dot descendants at z < 4 with the JWST
Year: 2025
Type: article
Abstract: Context. One of the most remarkable and unexpected results of the James Webb Space Telescope is the discovery of a population of compact red galaxies: the so-called little red dots (LRDs). The existence of these galaxies raises many questions, including that of their nature and origin, as well as that of their evolution. Indeed, these compact red sources exhibit a pronounced decline in number density by nearly two orders of magnitude from z = 6 to z = 3. Aims. In this paper, we investigate the possible evolution of this galaxy population at a lower redshift. To this end, we have identified a sample of candidates in the CEERS images that could represent the descendants of LRDs by assuming a single evolutionary path: the development of a blue star-forming outskirt while retaining a inner red core. Methods. Our color–magnitude selection identifies red galaxies as red as LRDs at z < 4, defined by a compact, red, inner region and blue outskirts. The red core is associated with the LRD population, while the blue periphery traces recently formed young stars. Morphological properties were derived by fitting single Sérsic profiles, while other physical quantities were obtained through spectral energy distribution (SED) fitting, assuming a stellar-only model for both the inner region and the outskirts. Results. The selected galaxies are likely “post-LRDs” galaxies, showing similar properties to LRDs under a stellar-only model: stellar masses of M * ≈ 10 10 M ⊙ , central densities Σ * ≈ 10 11 M ⊙ kpc −2 , similar rest-frame red colors, and a ∼1 kpc offset below the size–mass relation. Their number density at z = 3 ± 0.5 (10 −4.15 Mpc −3 ) matches that of LRDs at 5 < z < 7, supporting an evolutionary connection. We find a strong redshift-dependent increase in both outskirts’ mass fraction and galaxy size, from ∼250 pc at z = 5 to ∼600 pc at z = 3, indicating overall stellar growth. Meanwhile, the core remains as red and as massive, but the characteristic V shaped SED fades as the extended star-forming envelope becomes dominant. Conclusions. These findings support an evolutionary scenario in which LRDs gradually acquire an extended stellar component over cosmic time by cold accretion. This growth affects the initial LRD state in two key ways: the physical size increases and the characteristic V shaped SED in the core becomes less distinct and disappears. As a result, the original selection criteria based on both of them can no longer identify this population as it evolves, providing an explanation for their observed decline in number density.
Source: Astronomy and Astrophysics
Authors: Jean-Baptiste Billand, David Elbaz, Fabrizio Gentile, Maxime Tarrasse, Maximilien Franco, Benjamin Magnelli, Emanuele Daddi, Yipeng Lyu, Avishai Dekel, Fabio Pacucci, Valentina Sangalli, Mark Dickinson, Mauro Giavalisco, Benne W. Holwerda, Dale D. Kocevski, Anton M. Koekemoer, Vasily Kokorev, Ray A. Lucas, Pablo G. Pérez-González
Institutions: Centre National de la Recherche Scientifique, Université Paris Cité, Commissariat à l'Énergie Atomique et aux Énergies Alternatives, Université Paris-Saclay, Astrophysique, Instrumentation et Modélisation, Osservatorio di Astrofisica e Scienza dello Spazio, National Institute for Astrophysics, Hebrew University of Jerusalem, Harvard University, Center for Astrophysics Harvard & Smithsonian, NSF NOIRLab, University of Massachusetts Amherst, University of Louisville, Colby College, Space Telescope Science Institute, The University of Texas at Austin, Consejo Superior de Investigaciones Científicas, Centro de Astrobiología
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $1,865
OpenAlex ID: W4417004794