University of Portsmouth

About: University of Portsmouth is a education organization based out in Portsmouth, Portsmouth, United Kingdom. It is known for research contribution in the topics: Population & Galaxy. The organization has 5452 authors who have published 14256 publications receiving 424346 citations. The organization is also known as: Portsmouth and Gosport School of Science and Art & Portsmouth and Gosport School of Science and the Arts.

Stars in the braneworld

Abstract: We show that, in a Randall-Sundrum II type braneworld, the vacuum exterior of a spherical star is not in general a Schwarzschild spacetime, but has radiative-type stresses induced by five-dimensional graviton effects. Standard matching conditions do not lead to a unique exterior on the brane because of these five-dimensional graviton effects. We find an exact uniform-density stellar solution on the brane, and show that the general relativity upper bound $GM/Rl\frac{4}{9}$ is reduced by five-dimensional high-energy effects. The existence of neutron stars leads to a constraint on the brane tension that is stronger than the big bang nucleosynthesis constraint, but weaker than the Newton-law experimental constraint. We present two different non-Schwarzschild exteriors that match the uniform-density star on the brane, and we give a uniqueness conjecture for the full five-dimensional problem.

Galaxy Zoo: Passive Red Spirals .

Abstract: We study the spectroscopic properties and environments of red (or passive) spiral galaxies found by the Galaxy Zoo project. By carefully selecting face-on disc-dominated spirals, we construct a sample of truly passive discs (i.e. they are not dust reddened spirals, nor are they dominated by old stellar populations in a bulge). As such, our red spirals represent an interesting set of possible transition objects between normal blue spiral galaxies and red early types, making up ∼6 per cent of late-type spirals. We use optical images and spectra from Sloan Digital Sky Survey to investigate the physical processes which could have turned these objects red without disturbing their morphology. We find red spirals preferentially in intermediate density regimes. However, there are no obvious correlations between red spiral properties and environment suggesting that environment alone is not sufficient to determine whether a galaxy will become a red spiral. Red spirals are a very small fraction of all spirals at low masses (M★ < 1010 M⊙), but are a significant fraction of the spiral population at large stellar masses showing that massive galaxies are red independent of morphology. We confirm that as expected, red spirals have older stellar populations and less recent star formation than the main spiral population. While the presence of spiral arms suggests that a major star formation could not have ceased a long ago (not more than a few Gyr), we show that these are also not recent post-starburst objects (having had no significant star formation in the last Gyr), so star formation must have ceased gradually. Intriguingly, red spirals are roughly four times as likely than the normal spiral population to host optically identified Seyfert/low-ionization nuclear emission region (LINER; at a given stellar mass and even accounting for low-luminosity lines hidden by star formation), with most of the difference coming from the objects with LINER-like emission. We also find a curiously large optical bar fraction in the red spirals (70 ± 5 verses 27 ± 5 per cent in blue spirals) suggesting that the cessation of star formation and bar instabilities in spirals are strongly correlated. We conclude by discussing the possible origins of these red spirals. We suggest that they may represent the very oldest spiral galaxies which have already used up their reserves of gas – probably aided by strangulation or starvation, and perhaps also by the effect of bar instabilities moving material around in the disc. We provide an online table listing our full sample of red spirals along with the normal/blue spirals used for comparison.

Probing inflation with CMB polarization

Abstract: We summarize the utility of precise cosmic microwave background (CMB) polarization measurements as probes of the physics of inflation. We focus on the prospects for using CMB measurements to differentiate various inflationary mechanisms. In particular, a detection of primordial B‐mode polarization would demonstrate that inflation occurred at a very high energy scale, and that the inflaton traversed a super‐Planckian distance in field space. We explain how such a detection or constraint would illuminate aspects of physics at the Planck scale. Moreover, CMB measurements can constrain the scale‐dependence and non‐Gaussianity of the primordial fluctuations and limit the possibility of a significant isocurvature contribution. Each such limit provides crucial information on the underlying inflationary dynamics. Finally, we quantify these considerations by presenting forecasts for the sensitivities of a future satellite experiment to the inflationary parameters.