119217335
PRIMUS: ENHANCED SPECIFIC STAR FORMATION RATES IN CLOSE GALAXY PAIRS
Tidal interactions between galaxies can trigger star formation, which contributes to the global star formation rate (SFR) density of the universe and could be a factor in the transformation of blue, star-forming galaxies to red, quiescent galaxies over cosmic time. We investigate tidally triggered star formation in isolated close galaxy pairs drawn from the Prism Multi-Object Survey (PRIMUS), a low-dispersion prism redshift survey that has measured ∼ 120,000 robust galaxy redshifts over 9.1 deg 2 out to z ∼ 1. We select a sample of galaxies in isolated galaxy pairs at redshifts 0.25 ≤ z ≤ 0.75, with no other objects within a projected separation of 300 h ―1 kpc and Δz/(1 + z) = 0.01, and compare them to a control sample of isolated galaxies to test for systematic differences in their rest-frame FUV - r and NUV - r colors as a proxy for relative specific star formation rates (SSFRs). We find that galaxies in r p ≤ 50 h ―1 kpc pairs have bluer dust-corrected UV - r colors on average than the control galaxies by ―0.134 ± 0.045 mag in FUV - r and ―0.075 ± 0.038 mag in NUV - r, corresponding to an ∼ 15%―20% increase in SSFR. This indicates an enhancement in SSFR due to tidal interactions. We also find that this relative enhancement is greater for a subset of r p ≤ 30 h ―1 kpc pair galaxies, for which the average color offsets are ―0.193 ± 0.065 mag in FUV - r and ―0.159 ± 0.048 mag in NUV - r, corresponding to an ∼25%―30% increase in SSFR. We test for evolution in the enhancement of tidally triggered star formation with redshift across our sample redshift range and find marginal evidence for a decrease in SSFR enhancement from 0.25 ≤ z ≤ 0.5 to 0.5 ≤ z ≤ 0.75. This indicates that a change in enhanced star formation triggered by tidal interactions in low-density environments is not a contributor to the decline in the global SFR density across this redshift range.
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.
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
18491679
Galaxy Number Counts and Implications for Strong Lensing
We compare galaxy number counts in Advanced Camera for Surveys (ACS) fields containing moderate-redshift (0.2 <z <1.0) strong gravitational lenses with those in two control samples: (1) the first square degree of the COSMOS survey, comprising 259 ACS fields and (2) 20 ‘pure-parallel’ fields randomly located on the sky. Through a Bayesian analysis we determine the expectation values (μ0) and confidence levels of the underlying number counts for a range of apertures and magnitude bins. Our analysis has produced the following results: (i) we infer that our control samples are not consistent, with the number counts in the COSMOS sample being significantly higher than in the pure-parallel sample for 21 ≤F814W≤ 23. This result matches those found in previous analyses of COSMOS data using different techniques. (ii) We find that small-sized apertures, centred on strong lenses, are overdense compared with randomly placed apertures in the control samples, even compared to the COSMOS sample. Correcting for the local clustering of elliptical galaxies, based on the average two-point correlation function, reduces this overdensity to the 1-2σ level. Thus, the overdensity of galaxies seen along a typical line of sight to a lens can be explained mostly by the natural clustering of galaxies, rather than being due to lenses lying along otherwise biased lines of sight. However, a larger sample of lenses is needed to see if the remaining bias persists when the lens-field uncertainties are smaller. (iii) There is considerable scatter in the lines of sight to individual lens systems, but quantities that are linearly dependent on the external convergence (e.g. H0) should become unbiased if the extra galaxies that cause the bias can be accounted for in the lens models either through direct modelling or via an informed prior on the external convergence. The number counts can be used to set such an informed prior.
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
119230920
Reheating the Universe in Braneworld Cosmological Models with bulk-brane energy transfer
The emergence of the cosmological composition (the reheating era) after the inflationary period is analyzed in the framework of the braneworld models, in which our Universe is a three-brane embedded in a five-dimensional bulk, by assuming the possibility of the brane-bulk energy exchange. The inflaton field is assumed to decay into normal matter only, while the dark matter is injected into the brane from the bulk. To describe the reheating process we adopt a phenomenological approach, by describing the decay of the inflaton field by a friction term proportional to the energy density of the field. After the radiation dominated epoch the model reduces to the standard four dimensional cosmological model. The modified field equations are analyzed analytically and numerically in both the extra-dimensions dominate reheating phase (when the quadratic terms in energy density dominate the dynamics), and in the general case. The evolution profiles of the matter, of the scalar field and of the scale factor of the universe are obtained for different values of the parameters of the model, and of the equations of state of the normal and dark matter, respectively. The equation describing the time evolution of the ratio of the energy density of the dark and of the normal matter is also obtained. The ratio depends on the rate of the energy flow between the bulk and the brane. The observational constraint of an approximately constant ratio of the dark and of the baryonic matter requires that the dark matter must be non-relativistic (cold). The model predicts a reheating temperature of the order of 3 × 10 6 GeV, a brane tension of the order of 10 25 GeV 4 , and the obtained composition of the universe is consistent with the observational data.
119199675
Comments on the Monopole-Antimonopole Pair Solutions
Recently, the monopole-antimonopole pair and monopole-antimonopole chain solutions are solved with internal space coordinate system of -winding number m greater than one. However, we notice that it is also possible to solve these solutions numerically in terms of -winding number m = 1 instead. When m = 1, the exact asymptotic solutions at small and large distances are parameterized by a single integer parameter s. Here we once again study the monopole-antimonopole pair solution of the SU(2) YangMills-Higgs theory which belongs to the topological trivial sector numerically in its new form. This solution with -winding and -winding number one is parameterized by s = 0 at small r and s = 1 at large r.
18053468
Half-monopole and multimonopole
We would like to present some exact SU(2) Yang–Mills–Higgs monopole solutions of half-integer topological charge. These solutions can be just an isolated half-monopole or a multimonopole with topological magnetic charge ½m where m is a natural number. These static monopole solutions satisfy the first order Bogomol'nyi equations. The axially symmetric one-half monopole gauge potentials possess a Dirac-like string singularity along the negative z-axis. The multimonopole gauge potentials are also singular along the z-axis and possess only mirror symmetries.
119217960
Inflating wormholes in the braneworld models
The braneworld model, in which our Universe is a three-brane embedded in a five-dimensional bulk, allows the existence of wormholes, without any violation of the energy conditions. A fundamental ingredient of traversable wormholes is the violation of the null energy condition (NEC). However, in the braneworld models, the stress–energy tensor confined on the brane, threading the wormhole, satisfies the NEC. In conventional general relativity, wormholes existing before inflation can be significantly enlarged by the expanding spacetime. We investigate the evolution of an inflating wormhole in the braneworld scenario, in which the wormhole is supported by the nonlocal braneworld effects. As a first step in our study, we consider the possibility of embedding a four-dimensional braneworld wormhole into a five-dimensional bulk. The conditions for the embedding are obtained by studying the junction conditions for the wormhole geometry, as well as the full set of the five-dimensional bulk field equations. For the description of the inflation, we adopt the chaotic inflation model. We study the dynamics of the braneworld wormholes during the exponential inflation stage, and in the stage of the oscillating scalar field. A particular exact solution corresponding to a zero redshift wormhole is also obtained. The resulting evolution shows that while the physical and geometrical parameters of a zero redshift wormhole decay naturally, a wormhole satisfying some very general initial conditions could turn into a black hole and exist forever.
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.