3,886 research outputs found
Weak lensing evidence for a filament between A222/A223
We present a weak lensing analysis and comparison to optical and X-ray maps
of the close pair of massive clusters A222/223. Indications for a filamentary
connection between the clusters are found and discussed.Comment: 6 pages, 1 figure. To appear in Proc. IAU Colloquium 195: Outskirts
of Galaxy Clusters - Intense Life in the Suburbs. Version with higher
resolution available at
http://www.astro.uni-bonn.de/~dietrich/torino_proc.ps.g
The cosmic flow in the Local Supercluster: Tracing PSCz tidal influence through optimized Least Action Principle
We assess the extent to which the flux-limited PSCz redshift sample is
capable of accounting for the major share of mass concentrations inducing the
external tidal forces affecting the peculiar velocities within the Local
Supercluster (LS). The investigation is based upon a comparison of the ``true''
velocities in 2 large N-body simulations and their reconstruction from
``observation-mimicking'' mock catalogues. The mildly nonlinear ``mock'' LS and
PSCz velocities are analyzed by means of the Least Action Principle technique
in its highly optimized implementation of Nusser & Branchini's Fast Action
Method (FAM). For both model N-body Universes, we conclude that the dipolar and
quadrupolar force field implied by the PSCz galaxy distribution would indeed be
sufficiently representing the full external tidal force field.Comment: 2 pages, 1 figure, contribution to ``Where's the Matter? Tracing Dark
and Bright Matter with the New Generation of Large Scale Surveys'', June
2001, Treyer & Tresse Eds, Frontier Grou
PAMELA, DAMA, INTEGRAL and Signatures of Metastable Excited WIMPs
Models of dark matter with ~ GeV scale force mediators provide attractive
explanations of many high energy anomalies, including PAMELA, ATIC, and the
WMAP haze. At the same time, by exploiting the ~ MeV scale excited states that
are automatically present in such theories, these models naturally explain the
DAMA/LIBRA and INTEGRAL signals through the inelastic dark matter (iDM) and
exciting dark matter (XDM) scenarios, respectively. Interestingly, with only
weak kinetic mixing to hypercharge to mediate decays, the lifetime of excited
states with delta < 2 m_e is longer than the age of the universe. The
fractional relic abundance of these excited states depends on the temperature
of kinetic decoupling, but can be appreciable. There could easily be other
mechanisms for rapid decay, but the consequences of such long-lived states are
intriguing. We find that CDMS constrains the fractional relic population of
~100 keV states to be <~ 10^-2, for a 1 TeV WIMP with sigma_n = 10^-40 cm^2.
Upcoming searches at CDMS, as well as xenon, silicon, and argon targets, can
push this limit significantly lower. We also consider the possibility that the
DAMA excitation occurs from a metastable state into the XDM state, which decays
via e+e- emission, which allows lighter states to explain the INTEGRAL signal
due to the small kinetic energies required. Such models yield dramatic signals
from down-scattering, with spectra peaking at high energies, sometimes as high
as ~1 MeV, well outside the usual search windows. Such signals would be visible
at future Ar and Si experiments, and may be visible at Ge and Xe experiments.
We also consider other XDM models involving ~ 500 keV metastable states, and
find they can allow lighter WIMPs to explain INTEGRAL as well.Comment: 22 pages, 7 figure
Mapping the recreational value of coppicesâ management systems in Tuscany
In recent decades the growing interest in forested areas has led to a higher level of appreciation and consideration regarding the various benefits and services provided by forests. Despite this, when it comes to acknowledging their economic value and their capacity to produce income, the production of timber seems to be the main or even the only function that is considered. However, by adopting a sustainable forest management approach, the value related to non-market forest functions could also be considered. The present paper aims to quantify the potential income related to the recreational value of coppice forest by considering three different management systems: traditional coppice, active conversion to high forest and the natural evolution of forest. In order to do so, a contingent valuation method was used, and 248 forest users were surveyed in the region of Tuscany, Italy. The surveys included a revised price-list method, and the results obtained showed the existence of willingness to pay (WTP) for the maintenance of forests. Users showed a strong preference for conversion to high forest, while natural evolution was the least preferred management option. Peopleâs perception on this matter was also assessed based on their specific location, by georeferencing all of the respondentsâ answers: considering this, it was observed that belonging to a municipality located in or close to the mountains (i.e., mountain and natural municipalities) influenced the usersâ WTP to maintain natural evolution
Overdensities of Y-dropout Galaxies from the Brightest-of-Reionizing Galaxies Survey: A Candidate Protocluster at Redshift z~8
Theoretical and numerical modeling of dark-matter halo assembly predicts that
the most luminous galaxies at high redshift are surrounded by overdensities of
fainter companions. We test this prediction with HST observations acquired by
our Brightest of Reionizing Galaxies (BoRG) survey, which identified four very
bright z~8 candidates as Y-dropout sources in four of the 23 non-contiguous
WFC3 fields observed. We extend here the search for Y-dropouts to fainter
luminosities (M_* galaxies with M_AB\sim-20), with detections at >5sigma
confidence (compared to >8sigma confidence adopted earlier) identifying 17 new
candidates. We demonstrate that there is a correlation between number counts of
faint and bright Y-dropouts at >99.84% confidence. Field BoRG58, which contains
the best bright z\sim8 candidate (M_AB=-21.3), has the most significant
overdensity of faint Y-dropouts. Four new sources are located within 70arcsec
(corresponding to 3.1 comoving Mpc at z=8) from the previously known brighter
z\sim8 candidate. The overdensity of Y-dropouts in this field has a physical
origin to high confidence (p>99.975%), independent of completeness and
contamination rate of the Y-dropout selection. We modeled the overdensity by
means of cosmological simulations and estimate that the principal dark matter
halo has mass M_h\sim(4-7)x10^11Msun (\sim5sigma density peak) and is
surrounded by several M_h\sim10^11Msun halos which could host the fainter
dropouts. In this scenario, we predict that all halos will eventually merge
into a M_h>2x10^14Msun galaxy cluster by z=0. Follow-up observations with
ground and space based telescopes are required to secure the z\sim8 nature of
the overdensity, discover new members, and measure their precise redshift.Comment: Minor revision: ApJ accepted [17 pages (emulateapj style), 7 figures,
2 tables
The Spitzer Extragalactic Representative Volume Survey (SERVS): The Environments of High-z SDSS Quasi-Stellar-Objects
This paper presents a study of the environments of SDSS Quasi-Stellar-Objects
(QSOs) in the Spitzer Extragalactic Representative Volume Survey (SERVS). We
concentrate on the high-redshift QSOs as these have not been studied in large
numbers with data of this depth before. We use the IRAC 3.6-4.5{\mu}m colour of
objects and ancillary r-band data to filter out as much foreground
contamination as possible. This technique allows us to find a significant (>
4-{\sigma}) over-density of galaxies around QSOs in a redshift bin centred on z
~ 2.0 and a (> 2-{\sigma}) over-density of galaxies around QSOs in a redshift
bin centred on z ~ 3.3. We compare our findings to the predictions of a
semi-analytic galaxy formation model, based on the {\Lambda}CDM millennium
simulation, and find for both redshift bins that the model predictions match
well the source-density we have measured from the SERVS data.Comment: 13 pages, 12 figures, Accepted by Ap
Improved Upper Limits on the Stochastic Gravitational-Wave Background from 2009â2010 LIGO and Virgo Data
Gravitational waves from a variety of sources are predicted to superpose to create a stochastic background. This background is expected to contain unique information from throughout the history of the Universe that is unavailable through standard electromagnetic observations, making its study of fundamental importance to understanding the evolution of the Universe. We carry out a search for the stochastic background with the latest data from the LIGO and Virgo detectors. Consistent with predictions from most stochastic gravitational-wave background models, the data display no evidence of a stochastic gravitational-wave signal. Assuming a gravitational-wave spectrum of ΩGWĂ°fĂ ÂŒ Ωαðf=fref Ăα, we place 95% confidence level upper limits on the energy density of the background in each of four frequency bands spanning 41.5â1726 Hz. In the frequency band of 41.5â169.25 Hz for a spectral index of α ÂŒ 0, we constrain the energy density of the stochastic background to be ΩGWĂ°fĂ \u3c 5.6 Ă 10â6. For the 600â1000 Hz band, ΩGWĂ°fĂ \u3c 0.14Ă°f=900 HzĂ3, a factor of 2.5 lower than the best previously reported upper limits. We find ΩGWĂ°fĂ \u3c 1.8 Ă 10â4 using a spectral index of zero for 170â600 Hz and ΩGWĂ°fĂ \u3c 1.0Ă°f=1300 HzĂ3 for 1000â1726 Hz, bands in which no previous direct limits have been placed. The limits in these four bands are the lowest direct measurements to date on the stochastic background. We discuss the implications of these results in light of the recent claim by the BICEP2 experiment of the possible evidence for inflationary gravitational waves
The PAMELA Positron Excess from Annihilations into a Light Boson
Recently published results from the PAMELA experiment have shown conclusive
evidence for an excess of positrons at high (~ 10 - 100 GeV) energies,
confirming earlier indications from HEAT and AMS-01. Such a signal is generally
expected from dark matter annihilations. However, the hard positron spectrum
and large amplitude are difficult to achieve in most conventional WIMP models.
The absence of any associated excess in anti-protons is highly constraining on
any model with hadronic annihilation modes. We revisit an earlier proposal,
whereby the dark matter annihilates into a new light (<~GeV) boson phi, which
is kinematically constrained to go to hard leptonic states, without
anti-protons or pi0's. We find this provides a very good fit to the data. The
light boson naturally provides a mechanism by which large cross sections can be
achieved through the Sommerfeld enhancement, as was recently proposed.
Depending on the mass of the WIMP, the rise may continue above 300 GeV, the
extent of PAMELA's ability to discriminate electrons and positrons.Comment: 4 pages, 2 figures; v3 separated pions plot, references adde
A gravitational wave observatory operating beyond the quantum shot-noise limit: Squeezed light in application
Around the globe several observatories are seeking the first direct detection of gravitational waves (GWs). These waves are predicted by Einstein\u27s general theory of relativity(1) and are generated, for example, by black-hole binary systems(2). Present GW detectors are Michelson-type kilometre-scale laser interferometers measuring the distance changes between mirrors suspended in vacuum. The sensitivity of these detectors at frequencies above several hundred hertz is limited by the vacuum (zero-point) fluctuations of the electromagnetic field. A quantum technology-the injection of squeezed light(3)-offers a solution to this problem. Here we demonstrate the squeezed-light enhancement of GEO 600, which will be the GW observatory operated by the LIGO Scientific Collaboration in its search for GWs for the next 3-4 years. GEO 600 now operates with its best ever sensitivity, which proves the usefulness of quantum entanglement and the qualification of squeezed light as a key technology for future GW astronomy(4)
Search for long-lived gravitational-wave transients coincident with long gamma-ray bursts
Long gamma-ray bursts (GRBs) have been linked to extreme core-collapse supernovae from massive stars. Gravitational waves (GW) offer a probe of the physics behind long GRBs. We investigate models of long-lived (~10â1000 s) GW emission associated with the accretion disk of a collapsed star or with its protoneutron star remnant. Using data from LIGOâs fifth science run, and GRB triggers from the Swift experiment, we perform a search for unmodeled long-lived GW transients. Finding no evidence of GW emission, we place 90% confidence-level upper limits on the GW fluence at Earth from long GRBs for three waveforms inspired by a model of GWs from accretion disk instabilities. These limits range from FtoFcm-2, depending on the GRB and on the model, allowing us to probe optimistic scenarios of GW production out to distances as far as = 33 Mpc. Advanced detectors are expected to achieve strain sensitivities 10x better than initial LIGO, potentially allowing us to probe the engines of the nearest long GRBs
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