Pseudo Little Red Dot: An active black hole embedded in a dense and dusty, metal-poor starburst galaxy at z = 5.96

article Pseudo Little Red Dot: An active black hole embedded in a dense and dusty, metal-poor starburst galaxy at z = 5.96 published yes Karina I. Caputi author Ryan A. Cooper author Pierluigi Rinaldi author Rafael Navarro-Carrera author Edoardo Iani author 4053390a-6b68-11ef-9828-a3b8adef8d0a0000-0001-8386-3546 Abigail A. Tumborang author JoMa department We present a study of a pseudo little red dot with no metal lines (Pseudo-LRD-NOM), a highly magnified lowmass galaxy behind the lensing cluster A370 at z = 5.96. We classify this object as a pseudo-LRD because its red rest-frame optical color is contaminated by a prominent Hα line (with EW0 ≳ 800 Å) present in its JWST NIRSpec spectrum. Hα is dominated by a narrow component and also has a minor broad component indicative of an active black hole with MBH ≈ 5.6 × 10^6 M⊙. A narrow Hβ emission line is also detected (where the signal-tonoise ratio, S/N, is 8), producing a Balmer decrement (narrow) Hα/Hβ = 11. The rest-frame UV spectral slope is ßspec/uv = - 1.20 ± 0.28. All these features can be ascribed to high dust attenuation. However, no [O III]λ5007 or any other metal lines are detected in the spectrum, so [O III]5007/Hβ < 0.25, at odds with a simple dust attenuation explanation. Accounting for all the spectral properties requires the model of a starburst with moderate color excess E(B − V )≈0.2–0.5, high gas density (nH ≳ 10^6 cm^−3 ), and low- to extremely-low gas/stellar metallicities (Z = 0.01–0.1 Z⊙). The demagnified stellar mass is × 2.25+ 0 1 . . 8 3 3 0 10^7 M , and the stellar-mass surface density is = + * 418 M pc 310 725 2, similar to that of massive/nuclear star clusters. Pseudo-LRD-NOM provides evidence of massive black-hole growth occurring in a high-density, dusty starburst that is at the early stages of its chemical enrichment, and is likely a precursor to a real LRD. https://research-explorer.ista.ac.at/download/22814/22887/2026_AstrophysicalJour_Caputi.pdf application/pdfno IOP Publishing2026 eng The Astrophysical Journal 0004-637X 1538-4357 2601.1146610.3847/1538-4357/ae80b9 10072 Caputi KI, Cooper RA, Rinaldi P, Navarro-Carrera R, Iani E, Tumborang AA. Pseudo Little Red Dot: An active black hole embedded in a dense and dusty, metal-poor starburst galaxy at z = 5.96. The Astrophysical Journal. 2026;1007(2). doi:<a href="https://doi.org/10.3847/1538-4357/ae80b9">10.3847/1538-4357/ae80b9</a> Caputi, Karina I., et al. “Pseudo Little Red Dot: An Active Black Hole Embedded in a Dense and Dusty, Metal-Poor Starburst Galaxy at z = 5.96.” The Astrophysical Journal, vol. 1007, no. 2, 203, IOP Publishing, 2026, doi:<a href="https://doi.org/10.3847/1538-4357/ae80b9">10.3847/1538-4357/ae80b9</a>. Caputi, K. I., Cooper, R. A., Rinaldi, P., Navarro-Carrera, R., Iani, E., & Tumborang, A. A. (2026). Pseudo Little Red Dot: An active black hole embedded in a dense and dusty, metal-poor starburst galaxy at z = 5.96. The Astrophysical Journal. IOP Publishing. <a href="https://doi.org/10.3847/1538-4357/ae80b9">https://doi.org/10.3847/1538-4357/ae80b9</a> K. I. Caputi, R. A. Cooper, P. Rinaldi, R. Navarro-Carrera, E. Iani, and A. A. Tumborang, “Pseudo Little Red Dot: An active black hole embedded in a dense and dusty, metal-poor starburst galaxy at z = 5.96,” The Astrophysical Journal, vol. 1007, no. 2. IOP Publishing, 2026. Caputi KI, Cooper RA, Rinaldi P, Navarro-Carrera R, Iani E, Tumborang AA. 2026. Pseudo Little Red Dot: An active black hole embedded in a dense and dusty, metal-poor starburst galaxy at z = 5.96. The Astrophysical Journal. 1007(2), 203. Caputi, Karina I., Ryan A. Cooper, Pierluigi Rinaldi, Rafael Navarro-Carrera, Edoardo Iani, and Abigail A. Tumborang. “Pseudo Little Red Dot: An Active Black Hole Embedded in a Dense and Dusty, Metal-Poor Starburst Galaxy at z = 5.96.” The Astrophysical Journal. IOP Publishing, 2026. <a href="https://doi.org/10.3847/1538-4357/ae80b9">https://doi.org/10.3847/1538-4357/ae80b9</a>. K.I. Caputi, R.A. Cooper, P. Rinaldi, R. Navarro-Carrera, E. Iani, A.A. Tumborang, The Astrophysical Journal 1007 (2026). 228142026-09-06T22:01:56Z2026-09-09T12:19:54Z