Weak lensing, which is the deflection of light by matter along the line of sight, has proven to be an efficient method for constraining models of structure formation and reveal the nature of dark ...energy. So far, most weak-lensing studies have focused on the shear field that can be measured directly from the ellipticity of background galaxies. However, within the context of forthcoming full-sky weak-lensing surveys such as Euclid , convergence maps (mass maps) offer an important advantage over shear fields in terms of cosmological exploitation. While it carry the same information, the lensing signal is more compressed in the convergence maps than in the shear field. This simplifies otherwise computationally expensive analyses, for instance, non-Gaussianity studies. However, the inversion of the non-local shear field requires accurate control of systematic effects caused by holes in the data field, field borders, shape noise, and the fact that the shear is not a direct observable (reduced shear). We present the two mass-inversion methods that are included in the official Euclid data-processing pipeline: the standard Kaiser & Squires method (KS), and a new mass-inversion method (KS+) that aims to reduce the information loss during the mass inversion. This new method is based on the KS method and includes corrections for mass-mapping systematic effects. The results of the KS+ method are compared to the original implementation of the KS method in its simplest form, using the Euclid Flagship mock galaxy catalogue. In particular, we estimate the quality of the reconstruction by comparing the two-point correlation functions and third- and fourth-order moments obtained from shear and convergence maps, and we analyse each systematic effect independently and simultaneously. We show that the KS+ method substantially reduces the errors on the two-point correlation function and moments compared to the KS method. In particular, we show that the errors introduced by the mass inversion on the two-point correlation of the convergence maps are reduced by a factor of about 5, while the errors on the third- and fourth-order moments are reduced by factors of about 2 and 10, respectively.
Euclid preparation Martinet, N.; Schrabback, T.; Hoekstra, H. ...
Astronomy and astrophysics (Berlin),
07/2019, Letnik:
627
Journal Article
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In modern weak-lensing surveys, the common approach to correct for residual systematic biases in the shear is to calibrate shape measurement algorithms using simulations. These simulations must fully ...capture the complexity of the observations to avoid introducing any additional bias. In this paper we study the importance of faint galaxies below the observational detection limit of a survey. We simulate simplified
Euclid
VIS images including and excluding this faint population, and measure the shift in the multiplicative shear bias between the two sets of simulations. We measure the shear with three different algorithms: a moment-based approach, model fitting, and machine learning. We find that for all methods, a spatially uniform random distribution of faint galaxies introduces a shear multiplicative bias of the order of a few times 10
−3
. This value increases to the order of 10
−2
when including the clustering of the faint galaxies, as measured in the
Hubble
Space Telescope Ultra-Deep Field. The magnification of the faint background galaxies due to the brighter galaxies along the line of sight is found to have a negligible impact on the multiplicative bias. We conclude that the undetected galaxies must be included in the calibration simulations with proper clustering properties down to magnitude 28 in order to reach a residual uncertainty on the multiplicative shear bias calibration of a few times 10
−4
, in line with the 2 × 10
−3
total accuracy budget required by the scientific objectives of the
Euclid
survey. We propose two complementary methods for including faint galaxy clustering in the calibration simulations.
Context. Future weak lensing surveys, such as the Euclid mission, will attempt to measure the shapes of billions of galaxies in order to derive cosmological information. These surveys will attain ...very low levels of statistical error, and systematic errors must be extremely well controlled. In particular, the point spread function (PSF) must be estimated using stars in the field, and recovered with high accuracy. Aims. The aims of this paper are twofold. Firstly, we took steps toward a nonparametric method to address the issue of recovering the PSF field, namely that of finding the correct PSF at the position of any galaxy in the field, applicable to Euclid . Our approach relies solely on the data, as opposed to parametric methods that make use of our knowledge of the instrument. Secondly, we studied the impact of imperfect PSF models on the shape measurement of galaxies themselves, and whether common assumptions about this impact hold true in an Euclid scenario. Methods. We extended the recently proposed resolved components analysis approach, which performs super-resolution on a field of under-sampled observations of a spatially varying, image-valued function. We added a spatial interpolation component to the method, making it a true 2-dimensional PSF model. We compared our approach to PSFEx , then quantified the impact of PSF recovery errors on galaxy shape measurements through image simulations. Results. Our approach yields an improvement over PSFEx in terms of the PSF model and on observed galaxy shape errors, though it is at present far from reaching the required Euclid accuracy. We also find that the usual formalism used for the propagation of PSF model errors to weak lensing quantities no longer holds in the case of an Euclid -like PSF. In particular, different shape measurement approaches can react differently to the same PSF modeling errors.
During the COVID-19 pandemic, restrictive rules were imposed around the world to limit the spread of the virus. The present study aims to investigate how the pandemic and the consequent restrictions ...have affected the lives and oral health of Italian families with children aged 0-14 years.
Through a questionnaire distributed online from December 2020 to March 2021 the following aspects were investigated: family income during the pandemic, fear of the pandemic, dietary habits, perceived risk of infection in a dental practice and perceived children oral health status during the pandemic.
The pandemic has not drastically changed the socio-economic conditions, the dietary habits and the oral health condition of most Italian children. Nevertheless, the pandemic seems to have highlighted significant macro-regional differences regarding the satisfaction with the response of the regional health services to the pandemic. The continuation of the pandemic and the possible socio-economic effects could favour new changes in lifestyles, oral health and discrepancies regarding health care access, which deserve to be the subject of further investigation.
We have obtained the first successful interferometric measurements of asteroid sizes and shapes by means of the Very Large Telescope Interferometer-Mid-Infrared Interferometric Instrument ...(VLTI-MIDI). The VLTI can spatially resolve asteroids in a range of sizes and heliocentric distances that are not accessible to other techniques such as adaptive optics and radar. We have observed, as a typical bench mark, the asteroid (951) Gaspra, visited in the past by the Galileo space probe, and we derive a size in good agreement with the ground truth coming from the in situ measurements by the Galileo mission. Moreover, we have also observed the asteroid (234) Barbara, known to exhibit unusual polarimetric properties, and we found evidence of a potential binary nature. In particular, our data are best fit by a system of two bodies of 37 and 21 km in diameter, separated by a center-to-center distance of ~24 km (projected along the direction of the baseline at the epoch of our observations).
We present the first long baseline mid-infrared interferometric observations of the circumstellar disks surrounding Herbig Ae/Be stars. The observations were obtained using the mid-infrared ...interferometric instrument MIDI at the European Southern Observatory (ESO) Very Large Telescope Interferometer VLTI on Cerro Paranal. The 102 m baseline given by the telescopes UT1 and UT3 was employed, which provides a maximum full spatial resolution of 20 milli-arcsec (mas) at a wavelength of 10 μm. The interferometric signal was spectrally dispersed at a resolution of 30, giving spectrally resolved visibility information from 8 μm to 13.5 μm. We observed seven nearby Herbig Ae/Be stars and resolved all objects. The warm dust disk of HD 100546 could even be resolved in single-telescope imaging. Characteristic dimensions of the emitting regions at 10 μm are found to be from 1 AU to 10 AU. The 10 μm sizes of our sample stars correlate with the slope of the 10–25 μm infrared spectrum in the sense that the reddest objects are the largest ones. Such a correlation would be consistent with a different geometry in terms of flaring or flat (self-shadowed) disks for sources with strong or moderate mid-infrared excess, respectively. We compare the observed spectrally resolved visibilities with predictions based on existing models of passive centrally irradiated hydrostatic disks made to fit the SEDs of the observed stars. We find broad qualitative agreement of the spectral shape of visibilities corresponding to these models with our observations. Quantitatively, there are discrepancies that show the need for a next step in modelling of circumstellar disks, satisfying both the spatial constraints such as are now available from the MIDI observations and the flux constraints from the SEDs in a consistent way.
The Orion Nebula in the Mid-Infrared Robberto, M; Beckwith, S. V. W; Panagia, N ...
The Astronomical journal,
03/2005, Letnik:
129, Številka:
3
Journal Article
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We present two wide-field (5' X 35), diffraction-limited (l/D 05 at 10 mm), broadband 10 and 20 mm images of the Orion Nebula, plus six 7-13 mm narrowband (l/ lambda 1) images of the BN/KL complex ...taken at the 3.8 m UKIRT telescope with the MPIA MAX camera. The wide-field images, centered on the Trapezium and BN/KL regions, are mosaics of 35'' X 35'' frames obtained with standard chopping and nodding techniques and reconstructed using a new restoration method developed for this project. They show the filamentary structure of the dust emission from the walls of the H II region and reveal a new remarkable group of arclike structures 1' to the south of the Trapezium. The morphology of the Ney-Allen Nebula, produced by wind-wind interaction in the vicinity of the Trapezium stars, suggests a complex kinematical structure at the center of the cluster. We find indications that one of the most massive members of the cluster, the B0.5 V star c1 Ori D, is surrounded by a photoevaporated circumstellar disk. Among the four historic Trapezium OB stars, this is the only one without a binary companion, suggesting that stellar multiplicity and the presence of massive circumstellar disks may be mutually exclusive. In what concerns the BN/KL complex, we find evidence for extended optically thin silicate emission on top of the deep 10 mm absorption feature. Assuming a simple two-component model, we map with 05 spatial resolution the foreground optical depth, color temperature, and mid-IR luminosity of the embedded sources. We resolve a conspicuous point source at the location of the IRc2-A knot, approximately 05 north of the deeply embedded H II region 'I.' We analyze the spectral profile of the 10 mm silicate absorption feature and find indication for grain crystallization in the harsh nebular environment. In the OMC-1 South region, we detect several point sources and discuss their association with the mass-loss phenomenology observed at optical and millimeter wavelengths. Finally, we list the position and photometry of 177 point sources, the large majority of which are detected for the first time in the mid-IR. Twenty-two of them lack a counterpart at shorter wavelengths and are therefore candidates for deeply embedded protostars. The comparison of photometric data obtained at two different epochs reveals that source variability at 10 mm is present up to a level of 1 mag on a timescale of ~2 yr. With the possible exception of a pair of OB stars, all point sources detected at shorter wavelengths display 10 mm emission well above the photospheric level, which we attribute to disk circumstellar emission. The recent model of Robberto et al. provides the simplest explanation for the observed mid-IR excess.
The GAME mission concept is aimed at testing the General Relativity, through precise measurement of the gravitational deflection of light by the Sun, by means of an optimised telescope operating in ...the visible and launched in orbit on a small class satellite. We describe the proposed mission profile, the preliminary payload design and the expected performance. The targeted precision on the
γ parameter of the PPN formulation of General Relativity is in the range 10
−6 to 10
−7. The measurement principle relies on the differential astrometric signature on the stellar positions. The instrument concept is based on a dual field, multiple aperture Fizeau interferometer, observing simultaneously two sky regions close to the solar limb. A beam combiner folds the telescope line of sight on two different directions on the sky, separated by a base angle of 4°. The diluted optics approach achieves an efficient rejection of the scattered solar radiation, while retaining an acceptable angular resolution on the science targets.
The Very Large Telescope Interferometer (VLTI) of the European Southern Observatory (ESO) can be used to obtain direct determination of the sizes and the albedos of asteroids. We present results of ...the first attempt to carry out interferometric observations of asteroids with the Mid Infrared Interferometric Instrument (MIDI) at the VLTI. Our target was 1459 Magnya. This is the only V-type asteroid known to exist in the outer main-belt, and its IRAS-albedo turns out to be rather low for an object of this taxonomic class. Interferometric fringes were not detected, very likely due to the fact that the flux emitted by the asteroid was lower than expected and below the MIDI threshold for fringe detection. However, by fitting the Standard Thermal Model to the N-band infrared flux measured by MIDI in photometric mode and to the visible absolute magnitude, obtained from quasi-simultaneous B- and V-band photometric observations, we have derived a geometric visible albedo of
0.37
±
0.06
and an effective diameter of
17
±
1
km
. This new estimate of the albedo differs from that previously obtained by IRAS and is more consistent with the V-type taxonomic classification of 1459 Magnya.
Context.
Stage IV weak lensing experiments will offer more than an order of magnitude leap in precision. We must therefore ensure that our analyses remain accurate in this new era. Accordingly, ...previously ignored systematic effects must be addressed.
Aims.
In this work, we evaluate the impact of the reduced shear approximation and magnification bias on information obtained from the angular power spectrum. To first-order, the statistics of reduced shear, a combination of shear and convergence, are taken to be equal to those of shear. However, this approximation can induce a bias in the cosmological parameters that can no longer be neglected. A separate bias arises from the statistics of shear being altered by the preferential selection of galaxies and the dilution of their surface densities in high-magnification regions.
Methods.
The corrections for these systematic effects take similar forms, allowing them to be treated together. We calculated the impact of neglecting these effects on the cosmological parameters that would be determined from
Euclid
, using cosmic shear tomography. To do so, we employed the Fisher matrix formalism, and included the impact of the super-sample covariance. We also demonstrate how the reduced shear correction can be calculated using a lognormal field forward modelling approach.
Results.
These effects cause significant biases in Ω
m
,
σ
8
,
n
s
, Ω
DE
,
w
0
, and
w
a
of −0.53
σ
, 0.43
σ
, −0.34
σ
, 1.36
σ
, −0.68
σ
, and 1.21
σ
, respectively. We then show that these lensing biases interact with another systematic effect: the intrinsic alignment of galaxies. Accordingly, we have developed the formalism for an intrinsic alignment-enhanced lensing bias correction. Applying this to
Euclid
, we find that the additional terms introduced by this correction are sub-dominant.
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