Discovery of Powerful Multi-Velocity Ultra-Fast Outflows in the Starburst Merger Galaxy IRAS 05189$-$2524 with XRISM

TL;DR

XRISM PV observations of IRAS 05189-2524 reveal powerful multi-velocity ultra-fast outflows (UFOs) in a ULIRG, resolved in the Fe XXV/XXVI band by the X-ray microcalorimeter Resolve. The data require three UFO components with bulk velocities of $v_{\rm bulk}/c \sim 0.076$, 0.101, and 0.143 and distinct velocity dispersions, alongside a broad $\sim7$ keV emission line forming a P Cygni profile. Broadband Xtend data constrain a Compton-thin continuum with $N_{\rm H} \sim 7\times10^{22}$ cm$^{-2}$, $\Gamma \approx 2.3$, and $L_{ion}=4.1\times10^{44}$ erg s$^{-1}$, enabling robust wind energetics calculations. From the ionization and timing analyses, the UFOs are inferred to reside at $R \sim \mathcal{O}(10^3) R_S$ with clump sizes $\Delta R \sim 10^1$–$10^2 R_S$, yielding a total mass outflow rate $\dot{M}_{out} \sim 20\ M_{\odot}$ yr$^{-1}$, momentum flux $\dot{P}_{out} \sim 4.4\times10^{36}$ dyn, and kinetic power $\dot{E}_K \sim 8.0\times10^{45}$ erg s$^{-1}$, far exceeding the host galaxy’s molecular outflow and signaling strong AGN feedback during the ULIRG phase. These results imply that powerful UFOs are already prominent in this transitional stage and may drive the evolution toward a luminous quasar, sustaining wind activity and suppressing star formation.

Abstract

We observed the X-ray-bright ultra-luminous infrared galaxy, IRAS 05189$-$2524, with XRISM during its performance verification phase. The unprecedented energy resolution of the onboard X-ray microcalorimeter revealed complex spectral features at $\sim$7$-$9 keV, which can be interpreted as blueshifted Fe XXV/XXVI absorption lines with various velocity dispersions, originating from ultra-fast outflow (UFO) components with multiple bulk velocities of $\sim0.076c$, $\sim0.101c$, and $\sim0.143c$. In addition, a broad Fe-K emission line was detected around $\sim7$ keV, forming a P Cygni profile together with the absorption lines. The onboard X-ray CCD camera revealed a 0.4$-$12 keV broadband spectrum characterized by a neutrally absorbed power-law continuum with a photon index of $\sim2.3$, and intrinsic flare-like variability on timescales of $\sim10$ ksec, both of which are likely associated with near-Eddington accretion. We also found potential variability of the UFO parameters on a timescale of $\sim140$ ksec. Using these properties, we propose new constraints on the outflow structure and suggest the presence of multiple outflowing regions on scales of about tens to a hundred Schwarzschild radii, located within roughly two thousand Schwarzschild radii. Since both the estimated momentum and energy outflow rates of the UFOs exceed those of galactic molecular outflows, our results indicate that powerful, multi-velocity UFOs are already well developed during a short-lived evolutionary phase following a major galaxy merger, characterized by intense starburst activity and likely preceding the quasar phase. This system is expected to evolve into a quasar, sustaining strong UFO activity and suppressing star formation in the host galaxy.

Figures (5)

• Figure 1: The 5.0--10.5 keV Resolve spectrum and residuals in the fit with the model including the three-zone UFO components, shown in the rest frame. Panels (a) and (b) include a broad Gaussian and XSTAR emission model, respectively, while panel (c) shows the fit without any broad emission-line model. Red, purple, blue, green, and cyan show the total source spectrum, power-law continuum absorbed by UFOs, broad Gaussian emission line, narrow Fe-K$\alpha$ emission line, and the NXB spectrum, respectively. Vertical solid and dotted lines indicate the approximate positions of the Fe XXV/XXVI K$\alpha$ and K$\beta$ absorption features, respectively, in Zones 1 (red), 2 (green), and 3 (blue).
• Figure 2: (Left) The Xtend spectrum normalized with the effective area (black) shown with the spectra obtained by Chandra/ACIS (red and green), XMM-Newton/EPIC PN (orange, light green, and yellow-green), Suzaku/XIS (light blue), and NuSTAR (blue, cyan, magenta, and yellow) which were used in Yamada2021. (Right) The deconvolved Xtend spectrum in a $\nu F_{\nu}$ form fitted with the model of Abs$_{\rm Gal}$*$[$Abs$_{\rm int}$*$[$(three XSTAR$_{\rm UFO}$)*PL + Gauss + Fe-K$\alpha$$]$ + PL$_{\rm scat}$ + HostGal$]$. Both are shown in the observer frame.
• Figure 3: (Top) The 0.5--10 keV source (black) and background (grey) light curves derived by Xtend. (Middle) The 1.5--4 keV (red) and 4--10 keV (blue) light curves. (Bottom) The hardness ratio obtained by dividing the 4--10 keV count rate by the 1.5--4 keV count rate. The observation start time is 2024 August 9 17:34:01 (UT).
• Figure 4: Resolve spectra in the rest frame, divided into the first 140 ksec (black) and the latter 144 ksec (red). The black and red lines show the best-fit models for the first and latter intervals, respectively, obtained from a simultaneous fit using the model Abs$_{\rm Gal}$*Abs$_{\rm int}$*[$($three XSTAR$_{\rm UFO}$)*PL + Gauss + Fe-K$\alpha$], in which the UFO parameters were untied and allowed to vary freely. Vertical solid lines indicate the approximate positions of the Fe XXV/XXVI K$\alpha$ absorption lines in Zone 3 at the first interval (black) and the latter interval (red).
• Figure 5: Schematic picture of the UFO components with multi velocities and velocity dispersions in IRAS 05189$-$2524.