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.

Optimizing baryon acoustic oscillation surveys – I. Testing the concordance ΛCDM cosmology

Abstract: We optimize the design of future spectroscopic redshift surveys for constraining the dark energy via precision measurements of the baryon acoustic oscillations (BAOs), with particular emphasis on the design of the Wide-Field Multi-Object Spectrograph. We develop a model that predicts the number density of possible target galaxies as a function of exposure time and redshift. We use this number counts model together with fitting formulae for the accuracy of the BAO measurements to determine the effectiveness of different surveys and instrument designs. We search through the available survey parameter space to find the optimal survey with respect to the dark energy equation-of-state parameters according to the Dark Energy Task Force Figure-of-Merit, including predictions of future measurements from the Planck satellite. We optimize the survey to test the Lambda cold dark matter model, assuming that galaxies are pre-selected using photometric redshifts to have a constant number density with redshift, and using a non-linear cut-off for the matter power spectrum that evolves with redshift. We find that line-emission galaxies are strongly preferred as targets over continuum emission galaxies. The optimal survey covers a redshift range 0.8 < z < 1.4, over the widest possible area (6000 deg2 from 1500 h observing time). The most efficient number of fibres for the spectrograph is 2000, and the survey performance continues to improve with the addition of extra fibres until a plateau is reached at 10 000 fibres. The optimal point in the survey parameter space is not highly peaked and is not significantly affected by including constraints from upcoming supernovae surveys and other BAO experiments.

Constraints on braneworld inflation from CMB anisotropies

Abstract: We obtain observational constraints on Randall--Sundrum type II braneworld inflation using a compilation of data including WMAP, the 2dF and latest SDSS galaxy redshift surveys. We place constraints on three classes of inflation models (large-field, small-field and hybrid models) in the high-energy regime, which exhibit different behaviour compared to the low-energy case. The quartic potential is outside the $2\sigma$ observational contour bound for a number of $e$-folds less than 60, and steep inflation driven by an exponential potential is excluded because of its high tensor-to-scalar ratio. It is more difficult to strongly constrain small-field and hybrid models due to additional freedoms associated with the potentials, but we obtain upper bounds for the energy scale of inflation and the model parameters in certain cases. We also discuss possible ways to break the degeneracy of consistency relations and inflationary observables.

Estimating the amount of vorticity generated by cosmological perturbations in the early universe

Abstract: We estimate the amount of vorticity generated at second order in cosmological perturbation theory from the coupling between first order energy density and nonadiabatic pressure, or entropy, perturbations. Assuming power law input spectra for the source terms, and working in a radiation background, we calculate the wave number dependence of the vorticity power spectrum and its amplitude. We show that the vorticity generated by this mechanism is non-negligible on small scales, and hence should be taken into consideration in current and future cosmic microwave background experiments.

Constraining primordial non-Gaussianity using two galaxy surveys and CMB lensing

Abstract: Next-generation galaxy surveys will be able to measure perturbations on scales beyond the equality scale. On these ultra-large scales, primordial non-Gaussianity leaves signatures that can shed light on the mechanism by which perturbations in the early Universe are generated. We perform a forecast analysis for constraining local type non-Gaussianity and its two-parameter extension with a simple scale-dependence. We combine different clustering measurements from future galaxy surveys -- a 21cm intensity mapping survey and two photometric galaxy surveys -- via the multi-tracer approach. Furthermore we then include CMB lensing from a CMB Stage 4 experiment in the multi-tracer, which can improve the constraints on bias parameters. We forecast $\sigma(f_{\rm NL}) \simeq 0.9$ (1.4) by combining SKA1, a Euclid-like (LSST-like) survey, and CMB-S4 lensing. With CMB lensing, the precision on $f_{\rm NL}$ improves by up to a factor of 2, showing that a joint analysis is important. In the case with running of $f_{\rm NL}$, our results show that the combination of upcoming cosmological surveys could achieve $\sigma(n_{\rm NL}) \simeq 0.12$ (0.22) on the running index.

The evolution of the [O ii], H β and [O iii] emission line luminosity functions over the last nine billions years

Abstract: Emission line galaxies are one of the main tracers of the large-scale structure to be targeted by the next-generation dark energy surveys To provide a better understanding of the properties and statistics of these galaxies, we have collected spectroscopic data from the VVDS and DEEP2 deep surveys and estimated the galaxy luminosity functions (LFs) of three distinct emission lines, [O II] (lambda lambda 3726, 3729) (05 \textless z \textless 13), H beta (lambda 4861) (03 \textless z \textless 08) and [O III] (lambda 5007) (03 \textless z \textless 08) Our measurements are based on 35 639 emission line galaxies and cover a volume of similar to 10(7) Mpc(3) We present the first measurement of the H beta LF at these redshifts We have also compiled LFs from the literature that were based on independent data or covered different redshift ranges, and we fit the entire set over the whole redshift range with analytic Schechter and Saunders models, assuming a natural redshift dependence of the parameters We find that the characteristic luminosity (L-*) and density (phi(*)) of all LFs increase with redshift Using the Schechter model over the redshift ranges considered, we find that, for [O II] emitters, the characteristic luminosity L-*(z = 05) = 32 x 10(41) erg s(-1) increases by a factor of 27 +/- 02 from z = 05 to 13; for H beta emitters L-*(z = 03) = 13 x 10(41) erg s(-1) increases by a factor of 20 +/- 02 from z = 03 to 08; and for [O III] emitters L-*(z = 03) = 73 x 10(41) erg s(-1) increases by a factor of 35 +/- 04 from z = 03 to 08