Detecting intracluster gas motion in galaxy clusters: Mock Astro-E2 observations

We explore the detectability of bulk motions in the X-ray-emitting intracluster medium using a catalog of 1836 mock Astro-E2 observations of simulated clusters of galaxies. We generate high-resolution mock spectra for two observing strategies: a four-pointing mosaic and a single central pointing. Normalizing to 200 (400) photons in the iron Kα region for the mosaic (central) study, we fit Poisson realizations of each simulated spectrum to a velocity-broadened isothermal plasma emission model. We confirm that the velocity characteristics (mean and dispersion) returned by the spectral fittings are unbiased measures of the emission-weighted values within the observed region, with scatter ±55 km s-1. The maximum velocity difference between mosaic element pairs Δvmax has ~6% likelihood of being transonic (Δvmax ≥ 0.5cs), and the likelihood falls steeply, p ∝ (Δvmax/cs)-4, at high Mach number. The velocity-broadening parameter σv from the central pointing fit exceeds the thermal value in 49% of the cases, with again a σ tail at large dispersion. We present as case studies the clusters that yield the strongest signal for each observing strategy.