15254963
Lens Galaxy Properties of SBS 1520+530: Insights from Keck Spectroscopy and AO Imaging
We report on an investigation of the SBS 1520+530 gravitational lens system. We have used archival Hubble Space Telescope (HST) imaging, Keck spectroscopic data, and Keck adaptive optics (AO) imaging to study the lensing galaxy and its environment. The AO imaging has allowed us to fix the lens galaxy properties with a high degree of accuracy when performing the lens modeling, and the data indicate that the lens has an elliptical morphology and perhaps a disk. The new spectroscopic data suggest that previous determinations of the lens redshift may be incorrect, and we report an updated, although inconclusive, value z(lens) = 0.761. We have also spectroscopically confirmed the existence of several galaxy groups at approximately the redshift of the lens system. We create new models of the lens system that explicitly account for the environment of the lens, and we also include improved constraints on the lensing galaxy from our AO imaging. Lens models created with these new data can be well fit with a steeper than isothermal mass slope (α = 2.29, where ρ propto r−α) if H_0 is fixed at 72 km s^(-1) Mpc^(-1); isothermal models require H_0 similar to 50 km s^(-1) Mpc^(-1). The steepened profile may indicate that the lens is in a transient perturbed state caused by interactions with a nearby galaxy.
119254962
PRIMUS: THE DEPENDENCE OF AGN ACCRETION ON HOST STELLAR MASS AND COLOR
We present evidence that the incidence of active galactic nuclei (AGNs) and the distribution of their accretion rates do not depend on the stellar masses of their host galaxies, contrary to previous studies. We use hard (2-10 keV) X-ray data from three extragalactic fields (XMM-LSS, COSMOS, and ELAIS-S1) with redshifts from the Prism Multi-object Survey to identify 242 AGNs with L{sub 2-10keV} = 10{sup 42-44} erg s{sup -1} within a parent sample of {approx}25,000 galaxies at 0.2 < z < 1.0 over {approx}3.4 deg{sup 2} and to i {approx} 23. We find that although the fraction of galaxies hosting an AGN at fixed X-ray luminosity rises strongly with stellar mass, the distribution of X-ray luminosities is independent of mass. Furthermore, we show that the probability that a galaxy will host an AGN can be defined by a universal Eddington ratio distribution that is independent of the host galaxy stellar mass and has a power-law shape with slope -0.65. These results demonstrate that AGNs are prevalent at all stellar masses in the range 9.5< log M{sub *}/M{sub sun}<12 and that the same physical processes regulate AGN activity in all galaxies in this stellar mass range. While a higher AGN fraction maymore » be observed in massive galaxies, this is a selection effect related to the underlying Eddington ratio distribution. We also find that the AGN fraction drops rapidly between z {approx} 1 and the present day and is moderately enhanced (factor {approx}2) in galaxies with blue or green optical colors. Consequently, while AGN activity and star formation appear to be globally correlated, we do not find evidence that the presence of an AGN is related to the quenching of star formation or the color transformation of galaxies.« less
56333569
PRIMUS: OBSCURED STAR FORMATION ON THE RED SEQUENCE
We quantify the fraction of galaxies at moderate redshifts (0.1 < z < 0.5) that appear red-and-dead in the optical, but in fact contain obscured star formation detectable in the infrared (IR), with the PRIsm MUlti-object Survey (PRIMUS). PRIMUS has measured {approx}120,000 robust redshifts with a precision of {sigma}{sub z}/(1 + z) {approx} 0.5% over 9.1 deg{sup 2} of the sky to the depth of i {approx} 23 (AB), up to redshift z {approx} 1. We specifically targeted 6.7 deg{sup 2} fields with existing deep IR imaging from the Spitzer Space Telescope from the SWIRE and S-COSMOS surveys. We select in these fields an i-band flux-limited sample (i < 20 mag in the SWIRE fields and i < 21 mag in the S-COSMOS field) of 3310 red-sequence galaxies at 0.1 < z < 0.5 for which we can reliably classify obscured star-forming (SF) and quiescent galaxies using IR color. Our sample constitutes the largest galaxy sample at intermediate redshift to study obscured star formation on the red sequence, and we present the first quantitative analysis of the fraction of obscured SF galaxies as a function of luminosity. We find that on average, at L {approx} L*, about 15% of red-sequencemore » galaxies have IR colors consistent with SF galaxies. The percentage of obscured SF galaxies increases by {approx}8% per mag with decreasing luminosity from the highest luminosities to L {approx} 0.2 L*. Our results suggest that a significant fraction of red-sequence galaxies have ongoing star formation and that galaxy evolution studies based on optical color therefore need to account for this complication.« less
119270486
Monopole–antimonopole pair dyons with critical electric charges
In this paper, we investigate some electrically charged magnetic solutions of the SU(2) Yang–Mills–Higgs field theory in the net-zero topological charge sector. We only examine the case when the Higgs field vanishes at two points along the z-axis and when the Higgs field vanishes along a ring with the z-axis as its symmetry axis. We study the possible electric charges the dyons can carry in relation to the electric–magnetic charge separations and calculate the finite total energy and magnet dipole moment of these dyons. These stationary dyon solutions do not satisfy the first-order Bogomol’nyi equations and are non-BPS solutions. They are axially symmetric saddle-point solutions and are characterized by the electric charge parameter, −1 < η < 1, which determines the net electric charges of these dyons. These dyon solutions are solved numerically when the magnetic charges are n = 1, 2, 3, 4 and 5, and when the strength of the Higgs field potential is non-vanishing with λ = 1. When λ = 1, we found that the net electric charge approaches a finite critical value as η approaches ±1. Hence the electromagnetic charge separation, total energy and magnetic dipole moment of the dyon also approach a finite critical value.
118580751
Weyl fluid dark matter model tested on the galactic scale by weak gravitational lensing
The higher-dimensional Weyl curvature induces on the brane a new source of gravity. This Weyl fluid of geometrical origin (reducing in the spherically symmetric, static configuration to a dark radiation and dark pressure) modifies spacetime geometry around galaxies and has been shown to explain the flatness of galactic rotation curves. Independent observations for discerning between the Weyl fluid and other dark matter models are necessary. Gravitational lensing could provide such a test. Therefore we study null geodesics and weak gravitational lensing in the dark radiation dominated region of galaxies in a class of spherically symmetric braneworld metrics. We find that the lensing profile in the braneworld scenario is distinguishable from dark matter lensing, despite both the braneworld scenario and dark matter models fitting the rotation curve data. In particular, in the asymptotic regions, light deflection is 18% enhanced as compared to dark matter halo predictions. For a linear equation of state of the Weyl fluid, we further find a critical radius below which braneworld effects reduce, while above it they amplify light deflection. This is in contrast to any dark matter model, the addition of which always increases the deflection angle.
8117211
Monopole-antimonopole and vortex rings
The SU(2) Yang-Mills-Higgs theory supports the existence of monopoles, antimonopoles, and vortex rings. In this paper, we would like to present new exact static antimonopole-monopole-antimonopole (A-M-A) configurations. The net magnetic charge of these configurations is always −1, while the net magnetic charge at the origin is always +1 for all positive integer values of the solution’s parameter m. However, when m increases beyond 1, vortex rings appear coexisting with these AMA configurations. The number of vortex rings increases proportionally with the value of m. They are located in space where the Higgs field vanishes along rings. We also show that a single-point singularity in the Higgs field does not necessarily correspond to a structureless 1-monopole at the origin but to a zero-size monopole-antimonopole-monopole (MAM) structure when the solution’s parameter m is odd. This monopole is the Wu-Yang-type monopole and it possesses the Dirac string potential in the Abelian gauge. These exact solutions ...
118337254
QCD TOPOLOGY AND LATTICE PERTURBATION THEORY FROM MONTE CARL0 SIMULATIONS WITH IMPROVED STAGGERED FERMIONS
The staggered quark formulation is one of many ways to include fermions on the lattice. Dynamical simulations are now routinely done with improved staggered quark actions which are more efficient than other popular formalisms. In this thesis two research works on improved staggered fermions are presented. A systematic study of the staggered Dirac operator's spectral properties is first presented. It is a long standing belief that staggered fermions do not feel gauge field topology because of the lack of zero eigenvalues of the operator at finite lattice spacing. The existence of fermionic zero modes in topological nontrivial background gauge fields is required by the Atiyah-Singer index theorem. In this study we observe that eigenmodes with very small eigenvalue and large chirality appear if improved staggered operators are used. These small eigenmodes can be identified as the "zero modes" associated with the topology of the gauge fields. We have also compared the distribution of the remaining nonchiral modes with the predictions of Random Matrix Theory. Satisfactory agreement is obtained. In the second project perturbative expansions of Wilson loops are computed in full QCD from Monte Carlo simulations with improved staggered fermions. This approach provides a much simpler alternative to diagrammatic perturbation theory, and has previously been shown to be successful in reproducing the perturbation series in pure gauge theory. This method is applied here for the first time to unquenched QCD. Twisted boundary conditions are used to eliminate effects of zero momentum modes and to suppress tunneling between the degenerate Z3 vaccua. A new simulation algorithm, the rational hybrid Monte Carlo algorithm, with no finite step size error is also employed. This is the first time this algorithm has been used in a numerical application. Results are in excellent agreement with analytic perturbation theory; this provides an important cross-check of the perturbation theory input to a recent determination of the strong coupling am(MZ) by the HPQCD collaboration.
118343376
Inflation and late-time acceleration in braneworld cosmological models with varying brane tension
Braneworld models with variable brane tension λ introduce a new degree of freedom that allows for evolving gravitational and cosmological constants, the latter being a natural candidate for dark energy. We consider a thermodynamic interpretation of the varying brane tension models, by showing that the field equations with variable λ can be interpreted as describing matter creation in a cosmological framework. The particle creation rate is determined by the variation rate of the brane tension, as well as by the brane–bulk energy-matter transfer rate. We investigate the effect of a variable brane tension on the cosmological evolution of the Universe, in the framework of a particular model in which the brane tension is an exponentially dependent function of the scale factor. The resulting cosmology shows the presence of an initial inflationary expansion, followed by a decelerating phase, and by a smooth transition towards a late accelerated de Sitter type expansion. The varying brane tension is also responsible for the generation of the matter in the Universe (reheating period). The physical constraints on the model parameters, resulting from the observational cosmological data, are also investigated.