Prof Gavin Dalton

Abstract:

We present an analysis of the redshift-space power spectrum, P(k), of rich clusters of galaxies based on an automated cluster catalogue selected from the APM Galaxy Survey. We find that P(k) can be approximated by a power law, P(k)∝kn, with n ≈ -1.6 over the wavenumber range 0.04 < k < 0.1 h Mpc-1. Over this range of wavenumbers, the APM cluster power spectrum has the same shape as the power spectra measured for optical and IRAS galaxies. This is consistent with a simple linear bias model in which different tracers have the same power spectrum as that of the mass distribution, but shifted in amplitude by a constant biasing factor. On larger scales, the power spectrum of APM clusters flattens and appears to turn over on a scale k ∼ 0.03 h Mpc-1. We compare the power spectra estimated from simulated APM cluster catalogues with those estimated directly from cubical N-body simulation volumes, and find that the APM cluster survey should give reliable estimates of the true power spectrum at wavenumbers k ≳ 0.02 h Mpc-1. These results suggest that the observed turnover in the power spectrum may be a real feature of the cluster distribution, and that we have detected the transition to a near-scale-invariant power spectrum implied by observations of anisotropies in the cosmic microwave background radiation. The scale of the turnover in the cluster power spectrum is in good agreement with the scale of the turnover observed in the power spectrum of APM galaxies.

Abstract:

We present a summary of the identification content of the UK ROSAT Deep Survey. The survey is based on a 115ksec PSPC observation and comprises a sample of 70 sources to a flux limit of 2 x 10(-15) ergs cm(-2) s(-1) (0.5-2 keV). At bright fluxes the survey is dominated by broad line QSOs, at intermediate fluxes it contains a number of groups and clusters of galaxies, but at faint fluxes the survey contains many galaxies with narrow optical emission lines (NELGs). The average X-ray spectrum of the NELGs is harder than that of the QSOs and similar to that of the X-ray background. The NELGs have optical spectra similar to the majority of the field galaxy population in the same redshift range and may simply be the more luminous members of the emission line field galaxy population. Based on optical line ratios and X-ray/optical ratios, the NELGs, both as a sample and within individual galaxies, appear to be a mixture of starburst galaxies and true AGN.