Euclid

Abstract:

The principles of measuring the shapes of galaxies by a model-fitting approach are discussed in the context of shape measurement for surveys of weak gravitational lensing. It is argued that such an approach should be optimal, allowing measurement with maximal signal-to-noise ratio, coupled with estimation of measurement errors. The distinction between likelihood-based and Bayesian methods is discussed. Systematic biases in the Bayesian method may be evaluated as part of the fitting process, and overall such an approach should yield unbiased shear estimation without requiring external calibration from simulations. The principal disadvantage of model fitting for large surveys is the computational time required, but here an algorithm is presented that enables large surveys to be analysed in feasible computation times. The method and algorithm is tested on simulated galaxies from the Shear TEsting Programme (STEP). © 2007 The Authors.

Abstract:

We investigate a model of the coevolution of black holes and dark matter halos. The evolution of dark matter halos is based on the Press-Schechter theory. Assuming a simple relation between dark matter halos and supermassive black holes enables us to reproduce both the observed evolving hard X-ray luminosity function and the X-ray background.

Abstract:

There is growing interest in the possible link between the growth of supermassive black holes and the effect of feedback from them on galaxy growth. There are three areas of significant uncertainty: (i) the physics of the feedback; (ii) the prevalence and effectiveness of feedback; (iii) the link between the growth of black holes and their hosts. The 2QZ optical QSO survey indicates that luminous QSOs are relatively short-lived, and it has recently been shown that the observed bolometric luminosity density from all AGN and its evolution can be reproduced if black holes grew coevally with their galaxies, implying but not requiring a causal link between galaxy growth and black hole growth. At low redshifts there is some evidence that black hole and galaxy growth are starting to decouple.

Abstract:

We investigate the relation between the mass of super-massive black holes (Mbh) in QSOs and the mass of the dark matter halos hosting them (Mdh). We measure the widths of broad emission lines (Mgii lambda 2798, Civ lambda 1549) from QSO composite spectra as a function of redshift. These widths are then used to determine virial black hole mass estimates. We compare our virial black hole mass estimates to dark matter halo masses for QSO hosts derived by Croom et al. (2005) based on measurements of QSO clustering. This enables us to trace the Mbh-Mdh relation over the redshift range z=0.5 to 2.5. We calculate the mean zero-point of the Mbh-Mdh relation to be Mbh=10^(8.4+/-0.2)Msun for an Mdh=10^(12.5)Msun. These data are then compared with several models connecting Mbh and Mdh as well as recent hydrodynamical simulations of galaxy evolution. We note that the flux limited nature of QSO samples can cause a Malmquist-type bias in the measured zero-point of the Mbh-Mdh relation. The magnitude of this bias depends on the scatter in the Mbh-Mdh relation, and we reevaluate the zero-point assuming three published values for this scatter. (abridged)