First detection of ultra-fast outflows in a quiescent galaxy

Yerong Xu, Malgorzata Siudek, Victor Rodríguez Morales, Mar Mezcua, Hai-cheng Feng, Ciro Pinto, James N. Reeves, Stefano Bianchi, Valentina Braito, Luigi C. Gallo

First listed 2026-07-09 | Last updated 2026-07-07

Abstract

Outflows in active galactic nuclei (AGN) are recognized as a fundamental mechanism driving the co-evolution of supermassive black holes (SMBHs) and their host galaxies. Although powerful outflows are frequently detected in gas-rich, active star-forming galaxies, their existence and potential impact within gas-poor, quiescent galaxies remain poorly understood. We report the first detection of a powerful ultra-fast outflow (UFO) in a nearby quiescent galaxy KUG 1208+386, providing a multiscale analysis of AGN winds from nuclear to galactic scales. We detect a nuclear X-ray UFO with a velocity of $v_{out} \approx -0.07c$ and a kinetic power of $\dot{E}_{\rm UFO}=(0.8\mbox{--}6.5) \times 10^{43}$erg/s, sufficient to drive effective AGN feedback ($\dot{E}_{\rm UFO}/L_\mathrm{Edd}=(1\mbox{--}8)\%$) and far exceeding the galactic [OIII] outflow power $\sim 10^{40}$ erg/s. Host galaxy analysis reveals a massive quiescent system (specific star formation rate $\sim3\times10^{-12}\mathrm{yr}^{-1}$) that has been quenched $\sim$9 Gyr ago. The central AGN is obscured by a line-of-sight (LOS) column density of $\log (N_\mathrm{H}^\mathrm{LOS}/\mathrm{cm}^{-2})\sim23$ and the circumnuclear scattering material is Compton-thick $\log(N_\mathrm{H}^\mathrm{scatter}/\mathrm{cm}^{-2})=24.7^{+0.8}_{-0.5}$. The discovery of a nuclear UFO in a long-quenched massive galaxy challenges the paradigm that UFOs are exclusive to gas-rich, star-forming systems, suggesting instead that they are governed by the local circumnuclear environments, rather than the global gas reservoir. Our results indicate that episodic, powerful winds can maintain the quiescent state of KUG 1208+386 over Gyr timescales, supporting a wind-driven `maintenance' mode of AGN feedback that is distinct from the classical jet mode.

Short digest

This paper reports the first ultra-fast outflow detected in a quiescent galaxy, identifying a nuclear X-ray wind in the nearby Seyfert KUG 1208+386 with v_out about -0.07c from archival XMM-Newton and NuSTAR spectroscopy. The UFO carries (0.8-6.5) x 10^43 erg/s, or about 1-8% of the Eddington luminosity, far above the roughly 10^40 erg/s galactic [OIII] outflow power seen with DESI, while the nucleus is obscured by a line-of-sight column of log N_H about 23 and Compton-thick scattering material with log N_H about 24.7. Broadband SED fitting and stellar-population constraints show that KUG 1208+386 is a massive, long-quenched host with sSFR about 3 x 10^-12 yr^-1 and quenching around 9 Gyr ago. The result matters because it argues that powerful UFOs do not require a globally gas-rich, star-forming host, and instead can operate in a maintenance-feedback mode set by the local circumnuclear environment.

Key figures to inspect

• Figure 2. This is the core detection figure for the paper because it shows the X-ray spectra, the Fe-K residuals, and the absorption feature identified as the UFO. Readers can directly see how the wind-bearing model improves the fit and where the putative ultra-fast outflow sits relative to the continuum and Fe-K emission.
• Figure 3. This figure is the clearest visual support for the claim that the host is genuinely quiescent rather than just temporarily faint. The cumulative mass assembly and star-formation history show that most of the stellar mass formed early and that the galaxy has been quenched for about 9 Gyr, which is central to the paper’s novelty.
• Figure 4. This is the best synthesis figure for the paper’s physical interpretation. By comparing the momentum rate and velocity of the KUG 1208 outflow phases with benchmark AGN and with momentum- and energy-conserving expectations, it shows how a powerful nuclear UFO coexists with a much weaker large-scale ionized outflow and motivates the maintenance-mode feedback picture.
• Figure 10. This figure provides the optical spectroscopic evidence for the galactic-scale ionized outflow in the on-nucleus DESI data. The line decomposition around H-beta and H-alpha makes it clear which components are narrow, broad, intermediate, and outflowing, connecting the nuclear X-ray wind to the larger-scale emission-line kinematics.
• Figure 12. This figure underpins the host-galaxy classification by showing the broadband CIGALE fit and the stellar-population fit to the offset DESI spectrum. It is where the stellar mass and very low star-formation rate are anchored observationally, complementing the star-formation-history plot with the direct evidence that the host is a massive quiescent system.