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arXiv · 2512.10167

Spectrally Resolved Gas Kinematics in Cygnus A: XRISM Detects AGN Jet-induced Velocity Dispersion in Multi-temperature Gas

Anwesh Majumder·T. Heckman·J. Meunier·A. Simionescu·B. R. McNamara·L. Gu·A. Ptak·E. Hodges-Kluck·M. Yukita·M. W. Wise·N. Roy
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Abstract

We report spectral analysis on a 170 ks XRISM \textit{Resolve} exposure of the core of Cygnus A. Analyzing the full field of view spectrum in the $1.7-12.0$ keV band, we find evidence for two-temperature cluster gas. The hotter ($kT = 5.53 \pm 0.13$ keV) gas has a velocity dispersion of $261 \pm 13$ km s$^{-1}$ and a bulk velocity of $120 \pm 20$ km s$^{-1}$ with respect to the central galaxy. The cooler gas ($kT = 2.0^{+0.4}_{-0.3}$ keV) has an even broader velocity dispersion of $440 \pm 130$ km s$^{-1}$, with a systematic uncertainty of $120$ km s$^{-1}$. The relative line-of-sight velocity between the hotter and cooler gas can be as high as $450 \pm 140$ km s$^{-1}$. We interpret the high velocity dispersions as a combination of turbulence and bulk motion due to the cocoon shock. The upper limit on the non-thermal pressure fraction for the hotter gas is $7.7 \pm 0.7\%$. We associate the cooler gas with the central region ($<35$ kpc) and the hotter phase with the gas surrounding it ($35-100$ kpc). The total energy due to the kinetic motion is $5.1 \times 10^{60}$ erg, consistent with the energy associated with the central radio source. The kinetic energy injection rate is $6.9 \times 10^{44}-7.4 \times 10^{45}$ erg s$^{-1}$ under varying assumptions of injection timescales. The range of injection power is higher than the cooling luminosity, and thus the heating and cooling rates in Cygnus A are unbalanced.

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Anwesh Majumder, T. Heckman, J. Meunier, A. Simionescu, B. R. McNamara, L. Gu, A. Ptak, E. Hodges-Kluck, M. Yukita, M. W. Wise, N. Roy. 2025-12-10. Spectrally Resolved Gas Kinematics in Cygnus A: XRISM Detects AGN Jet-induced Velocity Dispersion in Multi-temperature Gas. https://arxiv.org/abs/2512.10167

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