4,287 research outputs found
The Universe at extreme magnification
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
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
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
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
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)
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 Ãndice 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 energÃa 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 especÃfica. 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
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 Rigorous Free-form Lens Model of Abell 2744 to Meet the Hubble Frontier Fields Challenge
Hubble Frontier Fields (HFF) imaging of the most powerful lensing clusters
provides access to the most magnified distant galaxies. The challenge is to
construct lens models capable of describing these complex massive, merging
clusters so that individual lensed systems can be reliably identified and their
intrinsic properties accurately derived. We apply the free-form lensing method
(WSLAP+) to A2744, providing a model independent map of the cluster mass,
magnification, and geometric distance estimates to multiply-lensed sources. We
solve simultaneously for a smooth cluster component on a pixel grid, together
with local deflections by the cluster member galaxies. Combining model
prediction with photometric redshift measurements, we correct and complete
several systems recently claimed, and identify 4 new systems - totalling 65
images of 21 systems spanning a redshift range of 1.4<z<9.8. The reconstructed
mass shows small enhancements in the directions where significant amounts of
hot plasma can be seen in X-ray. We compare photometric redshifts with
"geometric redshifts", finding a high level of self-consistency. We find
excellent agreement between predicted and observed fluxes - with a best-fit
slope of 0.999+-0.013 and an RMS of ~0.25 mag, demonstrating that our
magnification correction of the lensed background galaxies is very reliable.
Intriguingly, few multiply-lensed galaxies are detected beyond z~7.0, despite
the high magnification and the limiting redshift of z~11.5 permitted by the HFF
filters. With the additional HFF clusters we can better examine the
plausibility of any pronounced high-z deficit, with potentially important
implications for the reionization epoch and the nature of dark matter.Comment: Accepted for publication in ApJ with newly identified lensed images
in complete HFF dat
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