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.

Constraining Curvatonic Reheating

Abstract: We derive the first systematic observational constraints on reheating in models of inflation where an additional light scalar field contributes to primordial density perturbations and affects the expansion history during reheating. This encompasses the original curvaton model but also covers a larger class of scenarios. We find that, compared to the single-field case, lower values of the energy density at the end of inflation and of the reheating temperature are preferred when an additional scalar field is introduced. For instance, if inflation is driven by a quartic potential, which is one of the most favoured models when a light scalar field is added, the upper bound T(reh) < 5 × 10(4) GeV on the reheating temperature T(reh) is derived, and the implications of this value on post-inflationary physics are discussed. The information gained about reheating is also quantified and it is found that it remains modest in plateau inflation (though still larger than in the single-field version of the model) but can become substantial in quartic inflation. The role played by the vev of the additional scalar field at the end of inflation is highlighted, and opens interesting possibilities for exploring stochastic inflation effects that could determine its distribution.

Is the dynamics of scaling dark energy detectable

Abstract: We highlight the unexpected impact of nucleosynthesis and other early universe constraints on the detectability of scaling quintessence dynamics at late times, showing that such dynamics may well be invisible until the unveiling of the Stage-IV dark energy experiments (DUNE, JDEM, LSST, SKA). Nucleosynthesis strongly limits potential deviations from ΛCDM. Surprisingly, the standard Chevallier–Polarski–Linder parametrization, w(z) = w0+waz/(1+z), cannot match the nucleosynthesis bound for minimally coupled scaling fields. Given that such models are arguably the best-motivated alternatives to a cosmological constant these results may significantly impact future cosmological survey design and imply that dark energy may well be dynamical even if we do not detect any dynamics in the next decade.

Challenges for creating magnetic fields by cosmic defects

Abstract: We analyze the possibility that topological defects can act as a source of magnetic fields through the Harrison mechanism in the radiation era. We give a detailed relativistic derivation of the Harrison mechanism at first order in cosmological perturbations, and show that it is only efficient for temperatures above $T\ensuremath{\simeq}0.2\text{ }\text{ }\mathrm{keV}$. Our main result is that the vector metric perturbations generated by the defects cannot induce vorticity in the matter fluids at linear order, thereby excluding the production of currents and magnetic fields. We show that anisotropic stress in the matter fluids is required to source vorticity and magnetic fields. Our analysis is relevant for any mechanism whereby vorticity is meant to be transferred purely by gravitational interactions, and thus would also apply to dark matter or neutrinos.

SDSS-IV MaNGA: Faint quenched galaxies - I. Sample selection and evidence for environmental quenching

Abstract: Using kinematic maps from the Sloan Digital Sky Survey (SDSS) Mapping Nearby Galaxies at Apache Point Observatory (MaNGA) survey, we reveal that the majority of low-mass quenched galaxies exhibit coherent rotation in their stellar kinematics. Our sample includes all 39 quenched low-mass galaxies observed in the first year of MaNGA. The galaxies are selected with Mr > −19.1, stellar masses 109 M⊙ 1.9. They lie on the size–magnitude and σ–luminosity relations for previously studied dwarf galaxies. Just six (15 ± 5.7 per cent) are found to have rotation speeds ve, rot 5 × 1010 M⊙), supporting the hypothesis that galaxy–galaxy or galaxy–group interactions quench star formation in lowmass galaxies. The local bright galaxy density for our sample is ρproj = 8.2 ± 2.0 Mpc−2, compared to ρproj = 2.1 ± 0.4 Mpc−2 for a star-forming comparison sample, confirming that the quenched low-mass galaxies are preferentially found in higher density environments.