Dynamics of Intracluster Gas and Bulk Motions in Clusters

In this paper I briefly discuss progress in recent lines of research on the internal dynamics of clusters of galaxies that have been made possible thanks to improvements in current e-ray spectrometers that enable them to perform detailed spatially resolved spectroscopy. In particular, I focus on the study of bulk motion in intracluster gas and the nature of features called cold fronts.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/73040/1/annals.1350.022.pd

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 (ICM) using a catalog of 1,836 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. The maximum velocity difference between mosaic element pairs $\Delta v_{\rm max}$ has ~ 6% likelihood of being transonic ($\Delta v_{\rm max} \ge 0.5 c_s$), and the likelihood falls steeply, p \spropto (\Delta v_{\rm max}/c_s)^{-4}, at high Mach number. The velocity broadening parameter $\sigma_v$ from the central pointing fit exceeds the thermal value in 49% of the cases, with again a $\sigma_v^{-4}$ tail at large dispersion. We present as case studies the clusters that yield the strongest signal for each observing strategy.Comment: 13 pages, 20 figures. Submitted to ApJ. Version with postscript figures embedded in the text available at http://www.umich.edu/~apawl/astroe2/. Version 2 includes changes in response to referee report and corrects an error in optical depth estimate

Cosmic Filaments in Superclusters

Large-scale structure calculations show that modest overdensity filaments will connect clusters of galaxies and these filaments are reservoirs of baryons, mainly in gaseous form. To determine whether such filaments exist, we have examined the UV absorption line properties of three AGNs projected behind possible filaments in superclusters of galaxies; the AGNs lie within 3 Mpc of the centerlines of loci connecting clusters. All three lines of sight show absorption in Ly\alpha, Ly\beta, or/and OVI at redshifts within about 1300 km/s of the nearby galaxy clusters that would define the closest filaments. For one AGN, the absorption line redshifts are close to the emission line redshift of the AGN, so we cannot rule out self-absorption for this object. These absorption line associations with superclusters are unlikely to have occurred by chance, a result consistent with the presence of cosmic filaments within superclusters.Comment: 16 pages, 7 eps figures, Accepted for publication in Ap