Dynamics of AGN feedback in the X-ray bright East and Southwest arms of M87, mapped by XRISM

TL;DR

This work presents the first microcalorimeter-resolved map of gas dynamics in M87 using XRISM/Resolve, focusing on the East and Southwest X-ray arms shaped by AGN feedback. It demonstrates a distinct kinematic separation between the hot ambient ICM and cooler uplifted gas, with the cooler phase showing larger line-of-sight velocities and dispersions, supporting an uplift scenario driven by buoyant radio bubbles. While the hot gas remains dynamically quiescent, the cooler gas exhibits velocity offsets between arms that are robust against several model variations but remain sensitive to low-energy gain calibration, yielding a kinetic energy in the uplift that is a small fraction of the gravitational potential energy. These results provide important constraints for AGN feedback models and highlight the critical role of precise energy calibration for high-precision measurements of ICM dynamics.

Abstract

As the central galaxy in the nearest cluster, M87 provides the best spatial resolution for disentangling the complex interactions between AGN jets and the surrounding environment. We investigate the velocity structure of the multitemperature X-ray gas in M87, particularly in the eastern and southwestern arms associated with past AGN outbursts, using high-resolution spectroscopy from XRISM/Resolve. We analyze a mosaic of XRISM/Resolve observations covering the core of M87, fitting single- and multi-temperature models to spectra extracted from different regions and energy bands. We assess the line-of-sight velocities and velocity dispersions of the hotter ambient and cooler uplifted gas phases, and evaluate systematic uncertainties related to instrumental gain calibration. The hotter ICM phase, traced by Fe He-$α$ emission, shows velocity dispersions below $\sim100$ km/s, and no significant velocity shifts between the arms and a relaxed offset region, suggesting limited dynamical impact from older AGN lobes. In contrast, the cooler gas phase appears to exhibit larger line of sight velocity gradients up to several hundred km/s as well as a higher velocity dispersion than the ambient hot phase, although these conclusions remain tentative pending improvements in the robustness of the gain calibration at lower energies. The first microcalorimeter-resolved map of gas dynamics in M87 supports the uplift scenario for the X-ray arms, with the cooler gas in the east and southwest seemingly moving in opposite directions along the line of sight. The kinetic energy is a small fraction of the gravitational potential energy associated with the gas uplift, and XRISM further suggests that AGN-driven motions may be short-lived in the hot ambient ICM. These constraints provide important input towards shaping future models of AGN feedback.

Figures (7)

• Figure 1: Left: Chandra image of M87 in the 3-7 keV energy band. The sky regions used for ray tracing and arf generation are overplotted in white. We neglect scattering from regions located beyond 5.2 arcmin from the center (shown as the outer white circle), hence the image is set to zero here. Right: Chandra image of M87 in the 0.5-2 keV energy band, divided by a spherically symmetric beta model to highlight substructure related to AGN feedback. In particular the bright E and SW 'arms' can be easily seen. The four XRISM/Resolve fields of view used to map the core of M87 are shown in white. Both images correspond to the same sky coordinates.
• Figure 2: Spectra and best-fit single temperature models in the three energy bands considered here. When two ObsIDs cover the same region, the one with shorter exposure time is shown in silver.
• Figure 3: Velocity dispersion and line of sight velocity for each of the four pointings, for various fitted energy bands. Left: 2.-3. keV, middle: 3.0-4.2 keV, right: 6.-7. keV. For the SW pointing we also show separately, in a lighter shade, the results for SW1 and SW2. The darker bars at the top represent gain uncertainties of 0.3 eV, converted to velocity units at 2.5, 3.5, and 6.7 keV. The lighter bars in the left and middle panels additionally illustrate a gain error of 1.0 eV.
• Figure 4: Left: line of sight velocity of the cooler (blue) and hotter (red) gas phases, for each of the two arm pointings and each of the various models and assumptions discussed in Sections \ref{['sect:joint']}-\ref{['sect:joint_mosys']}. The $1\sigma$ statistical confidence interval of the l.o.s. velocity of the NW offset is shown as a light red band for comparison. This parameter is insensitive to the model variations, with a standard deviation of only 0.5 km/s between the different models presented. Right: corresponding velocity dispersions of the cooler and hotter gas.
• Figure 5: Comparison of the data and best fit two-temperature model for the C, E, and SW pointings. For the central pointing, we show the model described in Section \ref{['sect:multiT_c']}, while for the E and SW we plot 'model A' as described in Section \ref{['sect:joint']}. For SW, results for pointing SW1 are shown with dashed lines and gray data points, while for SW2 with solid lines and black data points. We zoom in on the 2--3 keV and 6--7 keV bands showcasing the strongest emission lines. The black solid/dashed curve represents the total model, the red curve the hotter thermal component, and the blue curve the cooler thermal component. In the C pointing, the gray line represents the AGN power-law. Scattered light and LMXB components are not explicitly shown in the interest of plot clarity, but are included in the black total model curve.