Beyond the Dot: An LRD-like Nucleus at the Heart of an IR-bright Galaxy and its Implications for High-redshift LRDs

Rinaldi, P; Rieke, GH; Wu, Z; Gilbert, CJE; Pacucci, F; Barchiesi, L; Alberts, S; Carniani, S; Bunker, AJ; Bhatawdekar, R; D'Eugenio, F; Ji, Z; Johnson, BD; Hainline, K; Kokorev, V; Kumari, N; Iani, E; Lyu, J; Maiolino, R; Parlanti, E; Robertson, BE; Sun, Y; Vignali, C; Williams, CC; Willmer, CNA

Journal article

Beyond the Dot: An LRD-like Nucleus at the Heart of an IR-bright Galaxy and its Implications for High-redshift LRDs

Abstract:: Abstract Little red dots (LRDs) are compact, red sources discovered by JWST at high redshift ( z ≳ 4), marked by distinctive “V-shaped” spectral energy distributions (SEDs) and often interpreted as rapidly accreting active galactic nuclei (AGNs). Their true nature remains unclear though, and their evolutionary connection to their lower-redshift counterparts is still poorly constrained. Thus, we present WISEA J123635.56+621424.2 (here dubbed the Saguaro), a z = 2.0145 galaxy in GOODS-North, as a possible analog of high-redshift LRDs and a potential missing link in their evolutionary path toward lower-redshift systems. It features a compact LRD-like nucleus surrounded by a face-on spiral host. Its connections to LRDs include the following: (1) its nuclear spectrum shows a clear “V-shaped” SED, and (2) when redshifted to z = 7, surface brightness dimming makes the host undetectable, thus mimicking an LRD. This suggests that high-redshift LRDs may be embedded in extended hosts. To test this, we stack rest-frame UV images of 99 photometrically selected LRDs, revealing faint, diffuse emission. Stacking in redshift bins reveals mild radial growth, consistent with the expected galaxy size evolution. A simple analytic model confirms that surface brightness dimming alone can explain their compact appearance. Lastly, we show that the Saguaro is not unique by describing similar objects from the literature at z ≲ 3.5. Taken together, our results support a scenario in which LRDs may not be a distinct population, but could be the visible nuclei of galaxies undergoing a short-lived, (perhaps) AGN-dominated evolutionary phase, with their compact, red appearance driven largely by observational biases.

Publication status:: Published

Peer review status:: Peer reviewed

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APA Style

Rinaldi, P., Rieke, G., Wu, Z., Gilbert, C., Pacucci, F., Barchiesi, L., Alberts, S., Carniani, S., Bunker, A., Bhatawdekar, R., D'Eugenio, F., Ji, Z., Johnson, B., Hainline, K., Kokorev, V., Kumari, N., Iani, E., Lyu, J., Maiolino, R., … Willmer, C. (2026). Beyond the Dot: An LRD-like Nucleus at the Heart of an IR-bright Galaxy and its Implications for High-redshift LRDs. The Astrophysical Journal, 1006(2), 205–205.

MLA Style

Rinaldi, P., et al. “Beyond the Dot: An LRD-like Nucleus at the Heart of an IR-Bright Galaxy and Its Implications for High-Redshift LRDs.” The Astrophysical Journal, vol. 1006, no. 2, 2026, pp. 205–05.

Chicago Style

Rinaldi, P., GH Rieke, Z. Wu, et al. 2026. “Beyond the Dot: An LRD-like Nucleus at the Heart of an IR-Bright Galaxy and Its Implications for High-Redshift LRDs.” The Astrophysical Journal 1006 (2): 205–.
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