Pulsars, transients and relativistic astrophysics

Abstract:

We review several ways in which X-ray observations are helping to tie down the physical parameters in radio lobes and jets, resolving most of the notorious uncertainties which afflict estimates from synchrotron emission alone. Together, the new results imply that the energy density of jet plasma is dominated by particles which do not contribute to the observed radiation, such as relativistic protons or mildly relativistic electrons, These components have long been hypothesised but their implications have often been ignored. Their presence substantially increases estimates of the energy budget for jet activity, and implies that jets may be an important heat source for the intracluster gas.

Abstract:

We discuss prospects for cluster detection via the Sunyaev-Zel'dovich (SZ) effect in a blank field survey with the interferometer array, the Arcminute MicroKelvin Imager (AMI). Clusters of galaxies selected in the SZ effect probe cosmology and structure formation with little observational bias, because the effect measures integrated gas pressure directly, and does so independently of cluster redshift. We use hydrodynamical simulations in combination with the Press-Schechter expression to simulate SZ cluster sky maps. These are used with simulations of the observation process to gauge the expected SZ cluster counts. Even with a very conservative choice of parameters we find that AMI will discover at least several tens of clusters every year with Mtot ≥ 1014M⊙; the numbers depend on factors such as the mean matter density, the density fluctuation power spectrum and cluster gas evolution. The AMI survey itself can distinguish between these to some degree, and parameter degeneracies are largely eliminated given optical and X-ray follow-up of these clusters; this will also permit direct investigation of cluster physics and what drives the evolution.