A quasar hatching from a buried red phase at z = 3.7

Zheng Ma, Yongda Zhu, Zhiyuan Ji, Eiichi Egami, Marcia J. Rieke, Xiaohui Fan, Jianwei Lyu, George H. Rieke, Fengwu Sun, Yang Sun, George D. Becker, Andrew J. Bunker, Francesco D'Eugenio, Xiangyu Jin, Ignas Juodžbalis, Weizhe Liu, Roberto Maiolino, Pierluigi Rinaldi, Feige Wang, Christopher N. A. Willmer, Yunjing Wu, Jinyi Yang, Junyu Zhang, Peixin Zhu

First listed 2026-07-28 | Last updated 2026-07-25

Abstract

We present JADES-GS 209777, previously cataloged as CANDELS J033238.02-274626.2, hereafter "the Hatchling," a red quasar at $z=3.711$. While the source has been reported in earlier deep-field catalogs, our multiwavelength analysis reveals a visible active nucleus still embedded in a dense gas- and dust-rich environment. Red quasar continua are often attributed to dust attenuation, including non-standard extinction curves, but the highly comprehensive multiwavelength data for this source provide direct constraints on the material being cleared. Using JWST/NIRSpec, NIRCam, MIRI, HST, MUSE, Chandra, ALMA, and VLA data, we detect broad emission lines and strong X-ray emission, showing that the active nucleus is at least partially exposed. We also detect H$α$ and He I absorption, indicating dense gas close to the nucleus. Kinematically disturbed O I, Mg II, Na D, and [O III] features, together with extended Ly$α$ emission over $\gtrsim 20$ kpc, further show that multiphase gas is being accelerated from the nuclear region into the host-galaxy environment. The ALMA detection reveals strong dust emission, with the inferred infrared luminosity placing the system in the ULIRG regime. The continuum is red and sharply declining toward the rest-frame UV, resembling compact red AGNs, and may reflect extreme dust attenuation, gas reprocessing, possible BAL-like absorption, or a combination of these effects. Regardless of which mechanism dominates the continuum shape, the line diagnostics show that the visible nucleus remains partially obscured by nearby material. The Hatchling therefore represents a unique opportunity to explore a poorly known transition phase in which feedback is likely clearing an enshrouded quasar and allowing it to emerge toward a more unobscured active nucleus.

Short digest

Ma et al. present JADES-GS 209777 ("the Hatchling"), a z=3.711 compact red quasar caught with an unusually complete JWST-to-radio data set while its nucleus is visible but still embedded in gas and dust. Broad Hα and Hβ plus strong X-rays establish a partially exposed Type-1 AGN, while redshifted Hα and blueshifted He I absorption, disturbed O I, Mg II, Na I D, and broad blueshifted [O III] reveal dense line-of-sight gas alongside multiphase nuclear clearing. ALMA places the source in the ULIRG regime, and extended Lyα over at least 20 kpc shows that the disturbed material reaches the circumgalactic environment. The Hatchling is therefore a rare direct case for a transitional, feedback-driven emergence phase between buried red AGN and an unobscured quasar, although its unusually red UV-optical continuum may combine extreme dust attenuation, reprocessing, and BAL-like absorption rather than having a single origin.

Key figures to inspect

• Figure 1. This multiwavelength overview establishes the central observational tension: a directly detected X-ray and broad-line AGN coexists with strong 1.2 mm dust emission and a sharply red UV-to-optical continuum. It is the best single figure for introducing why the Hatchling is interpreted as exposed yet still embedded.
• Figure 2. The resolved Hα, Hβ, He I λ10830, O I λ8446, and [O III] profiles provide the nucleus-scale evidence for the paper's emerging-quasar interpretation. Broad Balmer emission demonstrates a visible BLR, while Balmer and He I absorption plus the blueshifted [O III] wing show that dense gas and ionized outflow remain in the immediate environment.
• Figure 3. This figure extends the clearing argument beyond ionized gas: Mg II and Na I D absorption trace cool outflowing material, while the Lyα maps reveal kinematically complex emission on roughly 20 kpc scales. It is the clearest visualization of the claimed multiphase connection from the nuclear region into the host and circumgalactic medium.
• Figure 4. The black-hole--host comparison places the Hatchling in an intermediate growth regime, above local scaling relations but less extreme than the most overmassive high-redshift quasars and little red dots. This population-level context supports the proposed interpretation that it is an evolutionary waypoint rather than simply a fully mature unobscured quasar.
• Figure 6. The extinction-law comparison directly addresses the main continuum-shape caveat. Standard SMC, Milky Way, Calzetti, and gray AGN prescriptions do not reconstruct the full intrinsic quasar shape, whereas a small-grain model gives a closer phenomenological match, underscoring that the red continuum alone does not uniquely diagnose the obscuring physics.