XRISM Observations of A1795: Evidence for Low Turbulence and Resonant Scattering

Abstract We present high-resolution X-ray spectroscopic observations of the cool-core galaxy cluster A1795 obtained with XRISM/Resolve. The cluster was observed with two deep pointings: a 225 ks central exposure and a 113 ks northern exposure, extending to a projected radius of 320 kpc from the cluster center. Single-temperature fits reveal a clear radial gradient in the line-of-sight velocity dispersion, decreasing from 114 ± 11 km s −1 in the core to 68 ± 39 km s −1 at 320 kpc. The bulk velocities in the central regions are very low (22 ± 12 and 7 ± 21 km s −1 ), indicating no significant relative motion between the brightest cluster galaxy and the intracluster medium (ICM). Given that the central region includes the southward-extending cool gas tail, this result disfavors the “cooling-wake” scenario and instead supports an active galactic nuclei-uplift origin. We find that the nonthermal pressure fraction decreases with radius, from P NT / P T ≈ 2% in the core to ∼0.6% at 330 kpc, suggesting that the northern ICM of A1795 is largely quiescent. Two-temperature and split energy-band (2–4 keV and 6–7 keV) fits identify two gas phases within the central < 1 . ′ 5 region, providing strong evidence for multiphase gas in the cluster core. We detect a ∼14% resonant suppression of the optically thick Fe xxv w line in the center. Additionally, we observe a significant excess in the Fe xxv y line-flux relative to models. Accounting for uncertainties in the atomic data reduces this discrepancy, suggesting that atomic data uncertainties may contribute to the observed residual flux.