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

TL;DR

This study reports the discovery of multiple ultra-fast outflows in the galaxy IRAS 05189$-$2524 using XRISM, revealing complex spectral features and suggesting these powerful winds influence galaxy evolution during a post-merger starburst phase.

Contribution

First detection of multi-velocity ultra-fast outflows in IRAS 05189$-$2524 with XRISM, providing new insights into outflow structures and their role in galaxy evolution.

Findings

Detected ultra-fast outflows with velocities up to 0.143c.

Observed variability in outflow parameters on 140 ksec timescale.

Outflows have momentum and energy rates exceeding galactic molecular outflows.

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.