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.

Towards the Observation of Hawking Radiation in Bose–Einstein Condensates

Abstract: Acoustic analogues of black holes (dumb holes) are generated when a supersonic fluid flow entrains sound waves and forms a trapped region from which sound cannot escape. The surface of no return, the acoustic horizon, is qualitatively very similar to the event horizon of a general relativity black hole. In particular Hawking radiation (a thermal bath of phonons with temperature proportional to the "surface gravity") is expected to occur. In this note we consider quasi-one-dimensional supersonic flow of a Bose–Einstein condensate (BEC) in a Laval nozzle (converging-diverging nozzle), with a view to finding which experimental settings could magnify this effect and provide an observable signal. We discuss constraints and problems for our model and identify the issues that should be addressed in the near future in order to set up an experiment. In particular we identify an experimentally plausible configuration with a Hawking temperature of order 70 n K; to be contrasted with a condensation temperature of the order of 90 n K.

Empirical Hα emitter count predictions for dark energy surveys

Abstract: Future galaxy redshift surveys aim to measure cosmological quantities from the galaxy power spectrum. A prime example is the detection of baryonic acoustic oscillations, providing a standard ruler to measure the dark energy equation of state, w(z), to high precision. The strongest practical limitation for these experiments is how quickly accurate redshifts can be measured for sufficient galaxies to map the large-scale structure. A promising strategy is to target emission-line (i.e. star-forming) galaxies at high redshift (z∼ 0.5–2); not only is the space density of this population increasing out to z∼ 2, but also emission lines provide an efficient method of redshift determination. Motivated by the prospect of future dark energy surveys targeting Hα emitters at near-infrared wavelengths (i.e. z > 0.5), we use the latest empirical data to model the evolution of the Hα luminosity function out to z∼ 2 and thus provide predictions for the abundance of Hα emitters for practical limiting fluxes. We caution that the estimates presented in this work must be tempered by an efficiency factor, e, giving the redshift success rate from these potential targets. For a range of practical efficiencies and limiting fluxes, we provide an estimate of Graphic, where Graphic is the 3D galaxy number density and P0.2 is the galaxy power spectrum evaluated at k= 0.2 h Mpc−1. Ideal surveys must provide Graphic in order to balance shot-noise and cosmic variance errors. We show that a realistic emission-line survey (e= 0.5) could achieve Graphic out to z∼ 1.5 with a limiting flux of 10−16 erg s−1 cm−2. If the limiting flux is a factor of 5 brighter, then this goal can only be achieved out to z∼ 0.5, highlighting the importance of survey depth and efficiency in cosmological redshift surveys.

The power spectrum and bispectrum of SDSS DR11 BOSS galaxies II: cosmological interpretation

Abstract: We examine the cosmological implications of the measurements of the linear growth rate of cosmological structure obtained in a companion paper from the power spectrum and bispectrum monopoles of the Sloan Digital Sky Survey III Baryon Oscillation Spectroscopic Survey Data, Release 11, CMASS galaxies. This measurement was of f 0:43 8, where 8 is the amplitude of dark matter density uctuations, and f is the linear growth rate, at the eective redshift of the survey, ze = 0:57. In conjunction with Cosmic Microwave Background (CMB) data, interesting constraints can be placed on models with non-standard neutrino properties and models where gravity deviates from general relativity on cosmological scales. In particular, the sum of the masses of the three species of the neutrinos is constrained to m < 0:49 eV (at 95% condence level) when the f 0:43 8 measurement is combined with state-of-the-art CMB measurements. Allowing the eective number of neutrinos to vary as a free parameter does not significantly change these results. When we combine the measurement of f 0:43 8 with the complementary measurement of f 8 from the monopole and quadrupole of the twopoint correlation function we are able to obtain an independent measurements of f and 8. We obtain f = 0:63 0:16 and 8 = 0:710 0:086 (68% condence level). This is the

Constraints on primordial density perturbations from induced gravitational waves

Abstract: We consider the stochastic background of gravitational waves produced during the radiation-dominated hot big bang as a constraint on the primordial density perturbation on comoving length scales much smaller than those directly probed by the cosmic microwave background or large-scale structure. We place weak upper bounds on the primordial density perturbation from current data. Future detectors such as BBO and DECIGO will place much stronger constraints on the primordial density perturbation on small scales.

The effect of baryons on redshift space distortions and cosmic density and velocity fields in the EAGLE simulation

Abstract: We use the EAGLE galaxy formation simulation to study the effects of baryons on the power spectrum of the total matter and dark matter distributions and on the velocity fields of dark matter and galaxies. On scales $k{\stackrel{>}{{}_\sim}} 4{h\,{\rm Mpc}^{-1}}$ the effect of baryons on the amplitude of the total matter power spectrum is greater than $1\%$. The back-reaction of baryons affects the density field of the dark matter at the level of $\sim3\%$ on scales of $1\leq k/({h\,{\rm Mpc}^{-1}})\leq 5$. The dark matter velocity divergence power spectrum at $k{\stackrel{ }{{}_\sim}} 1{h\,{\rm Mpc}^{-1}}$ (for $\mu>0.5$), but for $|\vec{k}|\leq 0.4{h\,{\rm Mpc}^{-1}}$ it differs by less than $1\%$. We report vanishingly small baryonic velocity bias for haloes: the peculiar velocities of haloes with $M_{200}>3\times10^{11}{{\rm M}_{\odot}}$ (hosting galaxies with $M_{*}>10^9{{\rm M}_{\odot}}$) are affected at the level of at most $1~$km/s, which is negligible for $1\%$-precision cosmology. We caution that since EAGLE overestimates cluster gas fractions it may also underestimate the impact of baryons, particularly for the total matter power spectrum. Nevertheless, our findings suggest that for theoretical modelling of redshift space distortions and galaxy velocity-based statistics, baryons and their back-reaction can be safely ignored at the current level of observational accuracy. However, we confirm that the modelling of the total matter power spectrum in weak lensing studies needs to include realistic galaxy formation physics in order to achieve the accuracy required in the precision cosmology era.