arXiv subjects

Hannah McCall

Publications and source records attributed to Hannah McCall.

6 recordsLinked to original sources

arXiv2026

Kinematics of Weak Cool-Core Cluster A3571 Observed with XRISM: Low Cooling Rate Balanced by Low Heating Rate

Most XRISM galaxy cluster observations to date have focused on AGN feedback or actively merging systems. The weak cool-core cluster A3571 was observed in four XRISM Cycle 1 pointings, enabling the study of gas kinematics in a relaxed, AGN-feedback-free system. We present measurements of the velocity dispersion and bulk velocity in the core regions of A3571, out to $120$ kpc. The velocity dispersion is relatively uniform across all regions ($\sim100-120 ~\mathrm{km~s^{-1}}$), except in the northern gas sloshing elongation, where a $68\%$ upper limit of $68~\mathrm{km~s^{-1}}$ is obtained. The core Mach number and non-thermal pressure fraction of A3571 are lower than in the extremely relaxed cluster A2029 and below predictions from cosmological simulation suites. Despite relatively low velocity dispersion values, the derived turbulent heating rate is sufficient to offset cooling losses in all studied regions. This suggests that sloshing motions contribute significantly to the heating budget. Comparing XRISM observations of merging and relaxed clusters, we find that mergers exhibit an average Mach number of $0.29\pm0.07$, nearly twice that of the relaxed sample, which is consistent with predictions from non-radiative cosmological simulations. A3571 is a promising target for resonant scattering studies; however, simulations indicate that deeper observations are required to obtain reliable turbulent velocities via the $z/w$ line ratio.

astro-ph.GA↗

arXiv2026

Sloshing Motions in Abell 3571 Revealed by XRISM/Resolve Velocity Mapping

Minor mergers can induce sloshing motions in the intracluster medium, leaving characteristic signatures in the thermodynamic structure and gas kinematics of cluster cores. Abell 3571 is an X-ray-bright, apparently relaxed cluster at $z \sim 0.04$. We observed the central $\sim 300$ kpc region of Abell 3571 with four partially overlapping XRISM Resolve pointings, covering three contiguous Resolve fields to the north, south and east with a total exposure time of approximately 575 ks. The velocity dispersions are subsonic and are at the level of $\sim 100$--$150 \, \mathrm{km~ \, s^{-1}}$ across most regions. The cooler region associated with the northern surface-brightness excess is blueshifted by up to $\sim -60 \, \mathrm{km \, s^{-1}}$ relative to the brightest cluster galaxy (BCG), while the hotter region in the southern and eastern surface-brightness deficit regions is redshifted by up to $\sim 170 \, \mathrm{km \, s^{-1}}$. Numerical simulations suggest that this large-scale thermodynamic and kinematic asymmetry is broadly consistent with early-phase sloshing induced by an off-axis minor merger. Abell 3572, an X-ray-faint gas-poor cluster located 1.6 Mpc to the south, is a promising candidate for the perturber. Given the lack of clear signatures of prominent AGN feedback in Abell 3571, these results suggest that sloshing-driven gas redistribution may contribute to delaying the re-establishment of a strong cool core in Abell 3571.

astro-ph.HE↗

arXiv2026

The major cluster merger in Abell 2034 as seen by XRISM: Strong turbulence and spectral anomalies?

XRISM observations to date have shown that gas kinetic pressures in the intracluster medium (ICM) tend towards the low end of predictions from cosmological simulations. Here, we present a XRISM observation of the merging cluster Abell 2034, which exhibits the broadest emission lines yet observed in a galaxy cluster. We measure a velocity dispersion of ~470 km/s, corresponding to a kinetic pressure fraction of ~15%. This places A2034 at or above the high end of the theoretical predictions for similar-mass clusters. This large velocity dispersion may reflect Mach ~0.5 turbulence in the ICM and/or result from a core disruption driven by the ongoing head-on merger. We also detect a ~380 km/s gas bulk velocity gradient along the merger axis with an opposite sign to the galaxy velocity gradient, indicating a decoupling of the cluster galaxies (and dark matter) from the ICM. Finally, we report tentative evidence of several spectral anomalies, including a suppressed Fe He$\alpha$-z line, an enhanced Fe Ly$\alpha$-2 line, and a potential absorption feature at ~8.7 keV. The first two features may be explained by the combination of a multi-component ICM and a non-equilibrium ionization state in the wake of a merger shock. Deeper XRISM observations of this cluster are required to confirm these features. This work highlights the importance of kinematic measurements across a large sample of merging clusters as well as the need for deep XRISM observations to unveil more exotic physics in the ICM.

astro-ph.HE↗

arXiv2025

A Yin-Yang Galaxy Cluster Merger in Abell 1914 Revealed by XRISM

Hierarchical mergers of galaxy clusters play a key role in converting gravitational energy into thermal and kinetic energy in the local universe. Understanding this process requires the reconstruction of cluster merger geometry, with careful consideration of projection effects. With its unprecedented spectral resolution, XRISM enables the disentanglement of merging cluster components along the line-of-sight via X-rays for the first time. In this letter, we focus on the massive cluster A1914, a puzzling case wherein the galaxy and dark matter distribution appear to be in tension with the X-ray morphology. We present XRISM observations of A1914 focusing on the velocity structure of the intracluster medium (ICM). The Resolve full-array spectrum requires two merging components along the line-of-sight, with bulk velocities offset by $\sim$1000 km/s and velocity dispersions of $\sim$200 km/s. The sub-array maps of flux ratios, bulk velocity, and velocity dispersion show the two components are offset and overlapping in the plane of the sky, consistent with a major (mass ratio $\sim$3), near line-of-sight merger with a pericenter distance of $\sim$200 kpc. We conclude that the two subclusters create an overlapping spiral pattern, referred to as a ''yin-yang'' merger. This scenario is further supported by tailored hydrodynamical simulations of the A1914 merger, demonstrating that this type of merger can broadly reproduce the observed X-ray morphology, gas temperature map, gas velocity maps, dark matter distribution, and galaxy velocities. This work demonstrates the power of high-resolution X-ray spectroscopy, provided by XRISM, to resolve complex cluster merger geometries.

astro-ph.HE↗

arXiv2025

Decoding AGN Feedback with X-arithmetic: From Morphology to Physical Mechanisms

Feedback from Active Galactic Nuclei (AGN) is a key process in the evolution of massive halos in the Universe. New observational information on feedback is crucial for improving the implementation of the physics in numerical models. In this work, we apply a novel image-manipulation technique, termed 'X-arithmetic', to a sample of 15 galaxy clusters and groups deeply observed with Chandra. This technique decomposes perturbations in feedback-dominated regions into images excluding either (1) weak shocks and sound waves, (2) bubbles inflated by jets, or (3) cooling and slow gas motions (isobaric perturbations), enabling efficient spatial identification of these features without involving spectroscopic analysis. We confirm the nature of previously (spectroscopically-)identified features and newly establish the origin of other structures. We find that feedback produces multiple shocks in groups and massive galaxies, but only one to two shocks in clusters. Prominent isobaric structures are abundant around inner cavities in clusters, compared to almost no such structures in groups. These differences suggest that feedback effects are stronger in smaller-mass systems, possibly due to the shallower gravitational potential of groups or more violent feedback. Follow-up spectroscopy, guided by the X-arithmetic results, suggests that earlier-identified "isothermal shocks" could be a mix of isobaric and adiabatic structures. We applied X-arithmetic to galaxy cluster simulations, demonstrating its straightforward application and future potential for testing the feedback physics details in simulations. Our feasibility study shows that imaging data from future X-ray observatories like AXIS will be ideal for expanding X-arithmetic application to a larger sample of objects.

astro-ph.GA↗

arXiv2024

The SRG/eROSITA All-Sky Survey: View of the Virgo Cluster

As the closest galaxy cluster, the Virgo Cluster is an exemplary environment for the study of the large-scale filamentary structure and physical effects that are present in cluster outskirts but absent from the more easily studied inner regions. Here, we present an analysis of the SRG/eROSITA data from five all-sky surveys. eROSITA allows us to resolve the entire Virgo cluster and its outskirts on scales between 1 kpc and 3 Mpc, covering a total area on the sky of about 25$^\circ$ by 25$^\circ$. We utilized image manipulation techniques and surface brightness profiles to search for extended emission, surface brightness edges, and features in the outskirts. We employed a method of comparing mean and median profiles to measure gas clumping out to and beyond the virial radius. Surface brightness analysis of the cluster and individual sectors of the cluster reveal the full extent of previously identified cold fronts to the north and south. The emissivity bias due to gas clumping, which we quantify over three orders of magnitude in the radial range, is found to be mild, consistent with previous findings. We find uniform clumping measurements in all directions, with no enhancements along candidate filaments. We find an estimated virial gas mass of $M_{\mathrm{gas},r<r_{200}} = (1.98 \pm 0.70) \times 10^{13}$ M$_\odot$. Through imaging analysis we detect the presence of extended emission spanning 320\,kpc to the southwest of M49. The extension has a significance of 3.15$\sigma$ and is coincident with radio emission detected with LOFAR, which could be evidence of an accretion shock or turbulent reacceleration as the M49 group or background W' cloud falls into the cluster and interacts with the intracluster medium.

astro-ph.CO↗