Institute of Cosmology and Gravitation, University of Portsmouth

About: Institute of Cosmology and Gravitation, University of Portsmouth is a based out in . It is known for research contribution in the topics: Galaxy & Redshift. The organization has 297 authors who have published 1207 publications receiving 76919 citations.

Affine quantization of the Brans-Dicke theory: Smooth bouncing and the equivalence between the Einstein and Jordan frames

Abstract: In this work, we present a complete analysis of the quantization of the classical Brans-Dicke theory using the method of affine quantization in the Hamiltonian description of the theory. The affine quantization method is based on the symmetry of the phase space of the system, in this case the (positive) half-plane, which is identified with the affine group. We consider a Friedmann-Lema\^{\i}tre-Robertson-Walker type spacetime, and since the scale factor is always positive, the affine method seems to be more suited than the canonical quantization for our quantum cosmology. We find the wave function of the Brans-Dicke universe and its energy spectrum. A smooth bounce is expected at the semiclassical level in the quantum phase-space portrait. We also address the problem of equivalence between the Jordan and Einstein frames.

Combined analysis of Hubble and VLT photometry of the intermediate mass black hole ESO 243−49 HLX-1

Abstract: In this paper, we present a combined analysis of data obtained with theHubbleSpaceTelescope (HST), Very Large Telescope (VLT) and Swift X-ray telescope of the intermediate-mass black hole ESO 243−49 HLX-1 that were taken two months apart between 2010 September and November. Previous separate analyses of these data found that they were consistent with an irradiated accretion disc with contribution from either a very young or very old stellar population, and also indicated that the optical flux of the HLX-1 counterpart could be variable. Such variability could only be attributed to a varying accretion disc, so simultaneous analysis of all data sets should break the degeneracies in the model fits. We thus simultaneously fit the broad-band spectral energy distribution (SED) from near-infrared through to X-ray wavelengths of the two epochs of data with a model consisting of an irradiated accretion disc and a stellar population. We show that this combined analysis rules out an old stellar population, finding that the SED is dominated by emission from an accretion disc with moderate reprocessing in the outer disc around an intermediate-mass black hole imbedded in a young (∼20 Myr) stellar cluster with a mass of ∼10 5 M� . We also place an upper limit on the mass of an additional hidden old stellar population of ∼10 6 M� . However, optical r � -band observations of HLX-1 obtained with the Gemini-South telescope covering part of the decay from a later X-ray outburst are consistent with constant optical flux, indicating that the observed variability between the HST and VLT observations could be spurious caused by differences in the background subtraction applied to the two optical data sets. In this scenario, the contribution of the stellar population, and thus the stellar mass of the cluster, may be higher. Nonetheless, variability of <50 per cent cannot be ruled out by the Gemini data and thus they are still consistent within the errors with an exponential decay similar to that observed in X-rays.

Emulators for the nonlinear matter power spectrum beyond Λ CDM

Abstract: Accurate predictions for the nonlinear matter power spectrum are needed to confront theory with observations in current and near future weak-lensing and galaxy clustering surveys. We propose a computationally cheap method to create an emulator for modified gravity models by utilizing existing emulators for $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$. Using a suite of $N$-body simulations, we construct a fitting function for the enhancement of both the linear and nonlinear matter power spectrum in the commonly studied Hu-Sawicki $f(R)$ gravity model valid for wave numbers $k\ensuremath{\lesssim}5--10h\text{ }\text{ }{\mathrm{Mpc}}^{\ensuremath{-}1}$ and redshifts $z\ensuremath{\lesssim}3$. We show that the cosmology dependence of this enhancement is relatively weak so that our fit, using simulations coming from only one cosmology, can be used to get accurate predictions for other cosmological parameters. We also show that the cosmology dependence can, if needed, be included by using linear theory, approximate $N$-body simulations (such as comoving lagrangian acceleration) and semianalytical tools like the halo model. Our final fit can easily be combined with any emulator or semianalytical models for the nonlinear $\mathrm{\ensuremath{\Lambda}}\mathrm{CDM}$ power spectrum to accurately, and quickly, produce a nonlinear power spectrum for this particular modified gravity model. The method we use can be applied to fairly cheaply construct an emulator for other modified gravity models. As an application of our fitting formula, we use it to compute Fisher forecasts for how well galaxy clustering and weak lensing in a Euclid-like survey will be at constraining modifications of gravity.

Eight new quasar lenses from the sloan digital sky survey quasar lens search

Abstract: We report the discovery and confirmation of eight new two-image lensed quasars by the Sloan Digital Sky Survey (SDSS) Quasar Lens Search. The lenses are SDSS J0904+1512 (image separation {theta} = 1.''13, source redshift z{sub s} = 1.826), SDSS J1054+2733 ({theta} = 1.''27, z{sub s} = 1.452), SDSS J1055+4628 ({theta} = 1.''15, z{sub s} = 1.249), SDSS J1131+1915 ({theta} = 1.''46, z{sub s} = 2.915), SDSS J1304+2001 ({theta} = 1.''87, z{sub s} = 2.175), SDSS J1349+1227 ({theta} = 3.''00, z{sub s} = 1.722), SDSS J1455+1447 ({theta} = 1.''73, z{sub s} = 1.424), and SDSS J1620+1203 ({theta} = 2.''77, z{sub s} = 1.158). Three of them, SDSS J1055+4628, SDSS J1455+1447, and SDSS J1620+1203, satisfy the criteria for constructing our statistical sample for studying the cosmological model. Based on galactic absorption lines of the lens galaxies, we also derive lens redshifts of z{sub l} = 0.398 and z{sub l} = 0.513 for SDSS J1620+1203 and the previously discovered lens SDSS J0746+4403, respectively.

ASSESSMENT of SYSTEMATIC CHROMATIC ERRORS THAT IMPACT SUB-1% PHOTOMETRIC PRECISION in LARGE-AREA SKY SURVEYS

Abstract: Meeting the science goals for many current and future ground-based optical large-area sky surveys requires that the calibrated broadband photometry is stable in time and uniform over the sky to 1% precision or better. Past surveys have achieved photometric precision of 1-2% by calibrating the survey's stellar photometry with repeated measurements of a large number of stars observed in multiple epochs. The calibration techniques employed by these surveys only consider the relative frame-by-frame photometric zeropoint offset and the focal plane position-dependent illumination corrections, which are independent of the source color. However, variations in the wavelength dependence of the atmospheric transmission and the instrumental throughput induce source color-dependent systematic errors. These systematic errors must also be considered to achieve the most precise photometric measurements. In this paper, we examine such systematic chromatic errors using photometry from the Dark Energy Survey (DES) as an example. We define a natural magnitude system for DES and calculate the systematic errors on stellar magnitudes, when the atmospheric transmission and instrumental throughput deviate from the natural system. We conclude that the systematic chromatic errors caused by the change of airmass in each exposure, the change of the precipitable water vapor and aerosol in the atmosphere over time, and the non-uniformity of instrumental throughput over the focal plane, can be up to 2% in some bandpasses. We compare the calculated systematic chromatic errors with the observed DES data. For the test sample data, we correct these errors using measurements of the atmospheric transmission and instrumental throughput. The residual after correction is less than 0.3%. We also find that the errors for non-stellar objects are redshift-dependent and can be larger than those for stars at certain redshifts.