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

Abstract

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 K alpha 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 Delta nu(max) has similar to 6% likelihood of being transonic (Delta nu(max) >= 0.5c(s)), and the likelihood falls steeply, p proportional to (Delta nu(max)/c(s))(-4), at high Mach number. The velocity-broadening parameter sigma(nu) from the central pointing fit exceeds the thermal value in 49% of the cases, with again a sigma(nu)(-4) tail at large dispersion. We present as case studies the clusters that yield the strongest signal for each observing strategy.