Discovery of two little red dots transitioning into quasars

Shuqi Fu, Zijian Zhang, Danyang Jiang, Jie Chen, Linhua Jiang, Luis C. Ho, Kohei Inayoshi, Kaiyuan Chen, Jianwei Lyu, Fengwu Sun, Feige Wang, Jinyi Yang

First listed 2025-12-01 | Last updated 2025-12-01

Abstract

James Webb Space Telescope (JWST) has uncovered a new population of compact objects that show a unique V-shaped spectral energy distribution (SED) in the UV and optical wavelength range. These so-called "little red dots" (LRDs) often exhibit broad Balmer emission lines, indicative of the presence of active galactic nuclei (AGNs). They generally lack detection of X-ray, radio, and mid-IR radiation, which is fundamentally different from typical AGNs. Various models, including super-Eddington-accreting black holes enshrouded in dense and dust-poor gas, have been proposed to explain these features. However, the nature of LRDs remains debated, and their evolutionary fate is unclear. Here we report two unusual LRDs at redshift z = 2.868 and 2.925 that are in a transitional phase towards typical AGNs. Their V-shaped SEDs, compact optical morphology, and broad emission lines satisfy the defining criteria of LRDs. On the other hand, they exhibit intense X-ray, radio, and mid-IR radiation that is much stronger than previously known LRDs. These hybrid properties suggest that the dense gas envelope around their central black holes is dispersing, allowing high-energy photons and radio emission to escape. Meanwhile, a dust torus is forming. This finding provides a direct insight into the nature of LRDs and indicates that at least some LRDs will evolve into AGNs or quasars at later times.

Short digest

Reports two COSMOS LRDs—Forge I (z=2.868) and Forge II (z=2.925)—whose V-shaped UV–optical SEDs, compact morphologies, and broad Paschen/He I lines meet LRD criteria. Unlike typical LRDs, they show strong X-ray, radio, and mid-IR emission, moderate X-ray obscuration, a 6.4 keV Fe K line in Forge II, and unusually large year-scale X-ray variability while UV broad lines remain weak/absent. The spectra reveal strong He I absorption in both and rare Pa absorption in Forge II, indicating dense, low-ionization gas with mixed inflow/outflow kinematics as the envelope thins. Authors argue these hybrids are LRDs in transition, with dispersing dense gas and an emerging dust torus, implying some LRDs evolve into normal AGN/quasars.

Key figures to inspect

• Figure 1 (broadband SEDs + image stamps): verify the V-shaped SED with a turnover near the Balmer limit and point-like F444W morphology; note added mid-IR/radio/X-ray points that exceed typical LRD levels.
• Figure 2 (JWST/NIRCam F444W slitless spectra): inspect broad He I, Pa, and O I emission (FWHM ~ several 10^3 km/s) and the He I absorption in both sources; look for the rare Pa absorption in Forge II used for BLR-based MBH and dense-gas inference; compare with DESI/HST UV spectra lacking canonical broad UV lines.
• Extended Data Fig. 4 (X-ray spectrum of Forge II): check the 6.4 keV Fe K line detection and column-density constraints supporting only modest obscuration.
• Extended Data Fig. 5 (X-ray variability): examine multi-epoch XMM/Chandra light curves showing factor-of-few year-scale variability that outpaces typical AGN, contrasted with stable F115W imaging.
• Extended Data Fig. 7 (UV–X-ray and radio plane): see alpha_ox after nebular-based UV correction and the placement on the fundamental plane; confirm that radio loudness drops to radio-quiet once intrinsic UV is used.