Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010aas...21535106w&link_type=abstract
American Astronomical Society, AAS Meeting #215, #351.06; Bulletin of the American Astronomical Society, Vol. 42, p.534
Astronomy and Astrophysics
Astronomy
Scientific paper
The abundance of galaxy clusters as a function of mass and redshift depends sensitively on the background cosmology and can be used as a precision probe of dark energy if cluster masses can be efficiently extracted from observations. Using a set of N-body/hydrodynamical simulations of binary cluster mergers, we find that cluster merger events do not appreciably bias the relation between mass and the integrated Sunyaev-Zel'dovich parameter, allowing an accurate characterization of dark energy parameters. However, merging clusters reveal, through Mpc-scale synchrotron emission called radio halos and relics, a pervasive nonthermal component in the intracluster medium (ICM) that may add non-negligible pressure support and bias mass-observable relations based on the state of the ICM. The energy tied up in relativistic electrons, protons, and magnetic fields cannot be determined without a measurement of the magnetic field strength. One way to find the average magnetic field strength is to detect inverse Compton (IC) emission at hard X-ray energies in a cluster with a radio halo. From a joint XMM and Suzaku HXD spectral analysis of the Coma cluster, for which a detection of IC emission has been claimed (Rephaeli & Gruber 2002; Fusco-Femiano et al. 2004), we do not confirm this emission and instead derive an upper limit on the nonthermal flux 2.5 times below their detections. Due to the HXD's smaller field of view, however, all observations would be consistent if the IC emission is more extended than the radio halo, which is expected if the magnetic field strength declines with radius. We present a test of this hypothesis with data from the Swift BAT instrument, which in principle has no limiting field of view. Also, we present a survey of Swift hard X-ray emission for all radio halo and relic clusters, as well as for the flux-limited HIFLUGCS cluster sample.
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