9,055 research outputs found
Double lenses
The analysis of the shear induced by a single cluster on the images of a
large number of background galaxies is all centered around the curl-free
character of a well-known vector field that can be derived from the data. Such
basic property breaks down when the source galaxies happen to be observed
through two clusters at different redshifts, partially aligned along the line
of sight. In this paper we address the study of double lenses and obtain five
main results. (i) First we generalize the procedure to extract the available
information, contained in the observed shear field, from the case of a single
lens to that of a double lens. (ii) Then we evaluate the possibility of
detecting the signature of double lensing given the known properties of the
distribution of clusters of galaxies. (iii) As a different astrophysical
application, we demonstrate how the method can be used to detect the presence
of a dark cluster that might happen to be partially aligned with a bright
cluster studied in terms of statistical lensing. (iv) In addition, we show that
the redshift distribution of the source galaxies, which in principle might also
contribute to break the curl-free character of the shear field, actually
produces systematic effects typically two orders of magnitude smaller than the
double lensing effects we are focusing on. (v) Remarkably, a discussion of
relevant contributions to the noise of the shear measurement has brought up an
intrinsic limitation of weak lensing analyses, since one specific contribution,
associated with the presence of a non-vanishing two-galaxy correlation
function, turns out not to decrease with the density of source galaxies (and
thus with the depth of the observations).Comment: 40 pages, 15 figures. Accepted for publication in ApJ main journa
HST/ACS weak lensing analysis of the galaxy cluster RDCS 1252.9-2927 at z=1.24
We present a weak lensing analysis of one of the most distant massive galaxy
cluster known, RDCS 1252.9-2927 at z=1.24, using deep images from the Advanced
Camera for Survey (ACS) on board the Hubble Space Telescope (HST). By taking
advantage of the depth and of the angular resolution of the ACS images, we
detect for the first time at z>1 a clear weak lensing signal in both the i
(F775W) and z (F850LP) filters. We measure a 5-\sigma signal in the i band and
a 3-\sigma signal in the shallower z band image. The two radial mass profiles
are found to be in very good agreement with each other, and provide a
measurement of the total mass of the cluster inside a 1Mpc radius of M(<1Mpc) =
(8.0 +/- 1.3) x 10^14 M_\odot in the current cosmological concordance model h
=0.70, \Omega_m=0.3, \Omega_\Lambda=0.7, assuming a redshift distribution of
background galaxies as inferred from the Hubble Deep Fields surveys. A weak
lensing signal is detected out to the boundary of our field (3' radius,
corresponding to 1.5Mpc at the cluster redshift). We detect a small offset
between the centroid of the weak lensing mass map and the brightest cluster
galaxy, and we discuss the possible origin of this discrepancy. The cumulative
weak lensing radial mass profile is found to be in good agreement with the
X-ray mass estimate based on Chandr and XMM-Newton observations, at least out
to R_500=0.5Mpc.Comment: 38 pages, ApJ in press. Full resolution images available at
http://www.eso.org/~prosati/RDCS1252/Lombardi_etal_accepted.pd
El Roque de Los Muchachos Site Characteristics. III. Analysis of Atmospheric Dust and Aerosol Extinction
Canary Islands are normally interested by dominant North-East winds that, in
some meteorological conditions, can transport sand at high altitude from the
Sahara desert. The dust may affect the efficiency of the telescopes and
decreases the transparency of the sky. In order to maximize the scientific
return of the telescopes located at the ORM, we present an analysis of the
atmospheric dust content and its effects on astronomical observations. B, V and
I dust aerosol astronomical extinction are derived. Using a 5 years series
database of data taken from the four channel TNG dust monitor, we compute a
mean hourly and daily values of the dust content. We have detected particles
having size 0.3, 0.5, 1.0 and 5.0 um. Using a power law we have derived the
content of 10.0 um particles. We found a typical local dust concentration
ranging from 3x10^6 particles per cubic meter at 0.3 um, to 10^3 at 5.0 um and
10 at 10.0 um, increasing up to 3 order of magnitudes during the dust storms,
with a relative higher increase of 1.0, 5.0 and 10.0 um particles. The number
of local dust storm events is the same in winter- and summertime, but, the
average background and storm-related increases in the dust concentration in
summer are significantly higher than in winter. In a uniform approximation,
during the dust storms, an average height of the dust layer of 2.5 km above the
telescope is inferred. During the sand storms La Palma Island is affected by an
almost uniform layer extending up to 5 km above the sea level, down, at least
the height of the telescope. The visible extinction is dominated by particles
at 1.0, 5.0 and 10.0 um. In agreement with the results from Carlsberg Automatic
Meridian Circle (CAMC) we find a typical extinction during dust storms of about
0.2 mag/airmass.Comment: Accepted for publication in A&A. 9 pages, 11 figures. This work is
the continuation of a series of papers concerning a detailed study of the
Astroclimatology at ORM. The two previous papers (both Lombardi et al.) have
reference PASP.2006.118.1198-1204 and PASP.2007.119.292-30
El Roque de Los Muchachos Site Characteristics. II. Analysis of Wind, Relative Humidity and Air Pressure
In this paper we present an analysis of wind speed, wind direction, relative
humidity and air pressure taken at TNG, CAMC and NOT at Observatorio del Roque
de Los Muchachos, in the Canary Islands. Data are compared in order to check
local variations and both long term and short term trends of the microclimate.
Furthermore, influence of wind speed on the astronomical seeing is estimated to
the aim to better understand the influence of wide scale parameters on local
meteorological data. The three telescopes show different prevailing wind
direction, wind speed, relative humidity and air pressure confirming
differences in local microclimate. We found that seeing deteriorates when wind
speed is lower than 3.3 m/s. Comparison in terms of wind speed and high
relative humidity (> 90%) shows that TNG seems to have optimal observational
conditions with respect to CAMC and NOT. Air pressure analysis shows that ORM
is dominated by high pressure. Short time variations of pressure anticipate
temperature variations tipically by 2-3 hours, this property vanishes in time
scales higher than some hours and disappear in longer time scales.Comment: 10 pages, 9 figures, accepted for publication in PAS
Blackbody radiation shift in 87Rb frequency standard
The operation of atomic clocks is generally carried out at room temperature,
whereas the definition of the second refers to the clock transition in an atom
at absolute zero. This implies that the clock transition frequency should be
corrected in practice for the effect of finite temperature of which the leading
contributor is the blackbody radiation (BBR) shift. Experimental measurements
of the BBR shifts are difficult. In this work, we have calculated the blackbody
radiation shift of the ground-state hyperfine microwave transition in 87Rb
using the relativistic all-order method and carried out detailed evaluation of
the accuracy of our final value. Particular care is taken to accurately account
for the contributions from highly-excited states. Our predicted value for the
Stark coefficient, k_S=-1.240(4)\times 10^{-10}\text{Hz/(V/m)}^{2} is three
times more accurate than the previous calculation [1].Comment: 7 page
Search for tau neutrinos at PeV energies and beyond with the MAGIC telescopes
The MAGIC telescopes, located at the Roque de los Muchachos Observatory (2200
a.s.l.) in the Canary Island of La Palma, are placed on the top of a mountain,
from where a window of visibility of about 5 deg in zenith and 80 deg in
azimuth is open in the direction of the surrounding ocean. This permits to
search for a signature of particle showers induced by earth-skimming cosmic tau
neutrinos in the PeV to EeV energy range arising from the ocean. We have
studied the response of MAGIC to such events, employing Monte Carlo simulations
of upward-going tau neutrino showers. The analysis of the shower images shows
that air showers induced by tau neutrinos can be discriminated from the
hadronic background coming from a similar direction. We have calculated the
point source acceptance and the expected event rates, for a sample of generic
neutrino fluxes from photo-hadronic interactions in AGNs. The analysis of about
30 hours of data taken toward the sea leads to a point source sensitivity for
tau neutrinos at the level of the down-going point source analysis of the
Pierre Auger Observatory, if the AUGER observation time is dedicated to a
similar amount by MAGIC.Comment: Proceedings of EPS-HEP 2017, European Physical Society conference on
High Energy Physics, 5-12 July 2017, Venice, Italy. arXiv admin note:
substantial text overlap with arXiv:1708.0614
Interior penalty discontinuous Galerkin FEM for the -Laplacian
In this paper we construct an "Interior Penalty" Discontinuous Galerkin
method to approximate the minimizer of a variational problem related to the
Laplacian. The function is log H\"{o}lder
continuous and . We prove that the minimizers of the
discrete functional converge to the solution. We also make some numerical
experiments in dimension one to compare this method with the Conforming
Galerkin Method, in the case where is close to one. This example is
motivated by its applications to image processing.Comment: 26 pages, 2 figure
Beyond the pale?: the implications of the RSLG Report for non-CURL modern university libraries: Perspectives on the support libraries group: Final report
We have shown that the cluster-mass reconstruction method
which combines strong and weak gravitational lensing data, developed
in the first paper in the series, successfully reconstructs the
mass distribution of a simulated cluster. In this paper we apply the method to the
ground-based high-quality multi-colour data of RX J1347.5-114
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