Euclid

Abstract:

The next generation of weak gravitational lensing surveys is capable of generating good measurements of cosmological parameters, provided that, amongst other requirements, adequate redshift information is available for the background galaxies that are measured. It is frequently assumed that photometric redshift techniques provide the means to achieve this. Here we compare Bayesian and frequentist approaches to photometric redshift estimation, particularly at faint magnitudes. We identify and discuss the biases that are inherent in the various methods, and describe an optimum Bayesian method for extracting redshift distributions from photometric data.

Abstract:

We investigate the link between ionised Fe X-ray line emission and continuum emission in the bright nearby AGN, Mrk 766. A new long (433 ks) XMM-Newton observation is analysed, together with archival data from 2000 and 2001. The contribution from ionised line emission is measured and its time variations on short (5-20 ks) timescales are correlated with the continuum emission. The ionised line flux is found to be highly variable and to be strongly correlated with the continuum flux, demonstrating an origin for the ionised line emission that is co-located with the continuum emission. Most likely the emission is ionised reflection from the accretion disc within a few A.U. of the central black hole, and its detection marks the first time that such an origin has been identified other than by fitting to spectral line profiles. Future observations may be able to measure a time lag and hence achieve reverberation mapping of AGN at X-ray energies.

Abstract:

We analyse the redshift-space (z-space) distortions of quasi-stellar object (QSO) clustering in the 2-degree field instrument (2dF) QSO Redshift Survey (2QZ). To interpret the z-space correlation function, ξ(σ, π), we require an accurate model for the QSO real-space correlation function, ξ(r). Although a single power-law ξ(r) ξ r-γ model fits the projected correlation function [wp(σ)] at small scales, it implies somewhat too shallow a slope for both wp(σ) and the z-space correlation function, ξ(s), at larger scales (≳20 h-1 Mpc). Motivated by the form for ξ(r) seen in the 2dF Galaxy Redshift Survey (2dFGRS) and in standard A cold dark matter (COM) predictions, we use a double power-law model for ξ(r), which gives a good fit to ξ(s) and w p(σ). The model is parametrized by a slope of γ = 1.45 for 1 < r < 10 h-1 Mpc and γ = 2.30 for 10 < r < 40 h-1 Mpc. As found for the 2dFGRS, the value of β determined from the ratio of ξ(s)/ξ(r) depends sensitively on the form of ξ(r) assumed. With our double power-law form for ξ(r), we measure β(z = 1.4) = 0.32-0.11+0.09. Assuming the same model for ξ(r), we then analyse the z-space distortions in the 2QZ ξ(σ, π) and put constraints on the values of Ωm0 and β(z = 1.4), using an improved version of the method of Hoyle et al. The constraints we derive are Ωm0 = 0.35-0.13+0.19, β(z = 1.4) = 0.50-0.15+0.13 in agreement with our ξ(s)/ξ(r) results at the ∼1σ level. © 2005 RAS.

Abstract:

The 2dF QSO Redshift Survey (2QZ) has obtained redshifts for in excess of 23 000 QSOs selected by their u′, bJ, r colours using the 2-degree Field (2dF) facility at the Anglo-Australian Telescope (AAT). In this paper, we describe the creation of the input catalogue from UK Schmidt photographic plates. All the plate materials used are described along with the techniques developed for flat-fielding variations in the photometric response of photographic emulsions. The selection criteria used for the survey are defined and their rationale discussed. Finally, several simple astrometric and photometric tests are performed. These demonstrate that, over the majority of the parameter space covered by this survey (18.25

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