3,957 research outputs found

    The Universe at extreme magnification

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    Extreme magnifications of distant objects by factors of several thousand have recently become a reality. Small very luminous compact objects, such as supernovae (SNe), giant stars at z=1-2, Pop III stars at z>7 and even gravitational waves from merging binary black holes near caustics of gravitational lenses can be magnified to many thousands or even tens of thousands thanks to their small size. We explore the probability of such extreme magnifications in a cosmological context including also the effect of microlenses near critical curves. We show how a natural limit to the maximum magnification appears due to the presence of microlenses near critical curves. We use a combination of state of the art halo mass functions, high-resolution analytical models for the density profiles and inverse ray tracing to estimate the probability of magnification near caustics. We estimate the rate of highly-magnified events in the case of SNe, GW and very luminous stars including Pop III stars. Our findings reveal that future observations will increase the number of events at extreme magnifications opening the door not only to study individual sources at cosmic distances but also to constrain compact dark matter candidates.Comment: 22 pages and 11 figures. Matches accepted versiion in A&

    On the Structure of Noncommutative N=2 Super Yang-Mills Theory

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    We show that the recently proposed formulation of noncommutative N=2 Super Yang-Mills theory implies that the commutative and noncommutative effective coupling constants \tau(u) and \tau_{nc}(u) coincide. We then introduce a key relation which allows to find a nontrivial solution of such equation, thus fixing the form of the low-energy effective action. The dependence on the noncommutative parameter arises from a rational function deforming the Seiberg-Witten differential.Comment: 1+5 pages, LaTe

    Constraining the abundance of primordial black holes with gravitational lensing of gravitational waves at LIGO frequencies

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    Gravitational waves from binary black holes that are gravitationally lensed can be distorted by small microlenses along the line of sight. Microlenses with masses of a few tens of solar masses, and that are close to a critical curve in the lens plane, can introduce a time delay of a few millisecond. Such time delay would result in distinctive interference patterns in the gravitational wave that can be measured with current experiments such as LIGO/Virgo. We consider the particular case of primordial black holes with masses between 5 and 50 solar masses acting as microlenses. We study the effect of a population of primordial black holes constituting a fraction of the dark matter, and contained in a macrolens (galaxy or cluster), over gravitational waves that are being lensed by the combined effect of the macrolens plus microlenses. We find that at the typical magnifications expected for observed GW events, the fraction of dark matter in the form of compact microlenses, such as primordial black holes, can be constrained to percent level. Similarly, if a small percentage of the dark matter is in the form of microlenses with a few tens of solar masses, at sufficiently large magnification factors, all gravitational waves will show interference effects. These effects could have an impact on the inferred parameters. The effect is more important for macroimages with negative parity, which usually arrive after the macroimages with positive parity.Comment: 18 pages and 15 figure

    Free Form Lensing Implications for the Collision of Dark Matter and Gas in the Frontier Fields Cluster MACSJ0416.1-2403

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    We present a free form mass reconstruction of the massive lensing cluster MACSJ0416.1-2403 using the latest Hubble Frontier Fields data. Our model independent method finds that the extended lensing pattern is generated by two elongated, closely projected clusters of similar mass. Our lens model identifies new lensed images with which we improve the accuracy of the dark matter distribution. We find that the bimodal mass distribution is nearly coincident with the bimodal X-ray emission, but with the two dark matter peaks lying closer together than the centroids of the X-ray emisison. We show this can be achieved if the collision has occurred close to the plane and such that the cores are deflected around each other. The projected mass profiles of both clusters are well constrained because of the many interior lensed images, leading to surprisingly flat mass profiles of both components in the region 15-100 kpc. We discuss the extent to which this may be generated by tidal forces in our dynamical model which are large during an encounter of this type as the cores "graze" each other. The relative velocity between the two cores is estimated to be about 1200 km/s and mostly along the line of sight so that our model is consistent with the relative redshift difference between the two cD galaxies (dz = 0.04).Comment: 22 pages, 18 figures, 2 table

    A Multiinstitutional Spanish Master’s Program in Ecosystem Restoration: Vision and Four-Year Experience

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    Since 2006, an innovative, multiinstitutional Spanish Master in Ecosystem Restoration (MER) is jointly offered by four major public universities in Madrid. In view of the high student demand—about 900 applications this academic year for only 30 places, a remarkable 75% rate of professional poststudy employment in a period of economic crisis, and the high number (> 40) of prestigious organizations involved in the program, we consider the MER program, although still young, to be very promising for the long term. We explain the process to create the MER and achieve the results obtained thus far. We describe its organization, report its vital statistics in terms of students, and identify some strengths and weaknesses observed to date. The MER program has evolved as a network of knowledge and experience that links universities, lecturers, researchers, students, private and public companies, NGOs, and administration centers. Our aim is to help other groups that may want to launch similar graduate-level ecological restoration degree programs

    Factores que afectan el impacto pesquero sobre peces cartilaginosos en el sureste español (Mediterráneo Suroccidental)

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    We propose a global index of impact based on the relative vulnerability of the local population of every species and the further application of regression trees globally optimized with evolutionary algorithms to study the fishing impact on the cartilaginous fish in southeastern Spain. The fishing impact is much higher in areas of less than 40 m depth within 11 km of the Cape Palos marine reserve. The impact also depends on the state of the sea and the kind of habitat. Deep-sea habitats associated with hard substrata and sandy beds show the highest impact, and sublittoral muds and habitats associated with circa littoral rocks with moderate energy show the lowest impact. The fishing impact changes throughout the moon cycle, showing different day-scale patterns associated with different habitats and different species compositions. Finally, we show that the global optimization of the regression trees can be essential to find some important patterns and that these trees are a useful tool for determining which areas are considered to be more important in terms of protection, taking into account specifically the vulnerability of the local populations.Proponemos un índice global de impacto basado en la vulnerabilidad relativa de las poblaciones locales de cada una de las especies y la posterior aplicación de árboles de regresión globalmente optimizados con algoritmos evolutivos, para estudiar el impacto de la pesca en los peces cartilaginosos del sureste español. El impacto de la pesca es mucho mayor, dentro de los 11 km de la reserva marina de Cabo de Palos, en aquellas zonas de menos de 40 m de profundidad. El impacto también depende del estado de la mar y el tipo de hábitat. Los hábitats de aguas profundas asociados a sustrato duro y fondo arenoso muestran los máximos impactos, mientras que, tanto los fondos fangosos sublitorales como los hábitats rocosos circalitorales con moderada energía de las corrientes, muestran un menor impacto. Además, se dan cambios a lo largo del ciclo lunar en el impacto de la pesca, lo que significa que existen diferentes patrones diarios, asociados a distintos hábitats, con distinta composición específica. Finalmente, mostramos que la optimización global de los árboles de regresión es esencial para revelar patrones importantes y son una herramienta útil para determinar aquellas áreas mas importantes en términos de protección, teniendo en cuenta, concretamente, la vulnerabilidad de las poblaciones locales

    Hubble Frontier Field Free-Form Mass Mapping of the Massive Multiple-Merging Cluster MACSJ0717.5+3745

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    We examine the latest data on the cluster MACSJ0717.5+3745 from the Hubble Frontier Fields campaign. The critically lensed area is the largest known of any lens and very irregular making it a challenge for parametric modelling. Using our Free-Form method we obtain an accurate solution, identify here many new sets of multiple images, doubling the number of constraints and improving the reconstruction of the dark matter distribution. Our reconstructed mass map shows several distinct central substructures with shallow density profiles, clarifying earlier work and defining well the relation between the dark matter distribution and the luminous and X-ray peaks within the critically lensed region. Using our free-form method, we are able to meaningfully subtract the mass contribution from cluster members to the deflection field to trace the smoothly distributed cluster dark matter distribution. We find 4 distinct concentrations, 3 of which are coincident with the luminous matter. The fourth peak has a significant offset from both the closest luminous and X-ray peaks. These findings, together with dynamical data from the motions of galaxies and gas will be important for uncovering the potentially important implications of this extremely massive and intriguing system.Comment: 16 pages, 10 figures, 2 tables. Matches the verson submitted to mnras. New table (A2) included with additional system candidate

    A Free-Form Lensing Grid Solution for A1689 with New Mutiple Images

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    Hubble Space Telescope imaging of the galaxy cluster Abell 1689 has revealed an exceptional number of strongly lensed multiply-imaged galaxies, including high-redshift candidates. Previous studies have used this data to obtain the most detailed dark matter reconstructions of any galaxy cluster to date, resolving substructures ~25 kpc across. We examine Abell 1689 (hereafter, A1689) non-parametrically, combining strongly lensed images and weak distortions from wider field Subaru imaging, and we incorporate member galaxies to improve the lens solution. Strongly lensed galaxies are often locally affected by member galaxies, however, these perturbations cannot be recovered in grid based reconstructions because the lensing information is too sparse to resolve member galaxies. By adding luminosity-scaled member galaxy deflections to our smooth grid we can derive meaningful solutions with sufficient accuracy to permit the identification of our own strongly lensed images, so our model becomes self consistent. We identify 11 new multiply lensed system candidates and clarify previously ambiguous cases, in the deepest optical and NIR data to date from Hubble and Subaru. Our improved spatial resolution brings up new features not seen when the weak and strong lensing effects are used separately, including clumps and filamentary dark matter around the main halo. Our treatment means we can obtain an objective mass ratio between the cluster and galaxy components, for examining the extent of tidal stripping of the luminous member galaxies. We find a typical mass-to-light ratios of M/L_B = 21 inside the r<1 arcminute region that drops to M/L_B = 17 inside the r<40 arcsecond region. Our model independence means we can objectively evaluate the competitiveness of stacking cluster lenses for defining the geometric lensing-distance-redshift relation in a model independent way.Comment: 23 pages with 25 figures Replced with MNRAS submitted version. Some figures have been corrected and minor text edit
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