32,268 research outputs found
XMMPZCAT: A catalogue of photometric redshifts for X-ray sources
The third version of the XMM-Newton serendipitous catalogue (3XMM),
containing almost half million sources, is now the largest X-ray catalogue.
However, its full scientific potential remains untapped due to the lack of
distance information (i.e. redshifts) for the majority of its sources. Here we
present XMMPZCAT, a catalogue of photometric redshifts (photo-z) for 3XMM
sources. We searched for optical counterparts of 3XMM-DR6 sources outside the
Galactic plane in the SDSS and Pan-STARRS surveys, with the addition of near-
(NIR) and mid-infrared (MIR) data whenever possible (2MASS, UKIDSS, VISTA-VHS,
and AllWISE). We used this photometry data set in combination with a training
sample of 5157 X-ray selected sources and the MLZ-TPZ package, a supervised
machine learning algorithm based on decision trees and random forests for the
calculation of photo-z. We have estimated photo-z for 100,178 X-ray sources,
about 50% of the total number of 3XMM sources (205,380) in the XMM-Newton
fields selected to build this catalogue (4208 out of 9159). The accuracy of our
results highly depends on the available photometric data, with a rate of
outliers ranging from 4% for sources with data in the optical+NIR+MIR, up to
40% for sources with only optical data. We also addressed the reliability
level of our results by studying the shape of the photo-z probability density
distributions.Comment: 16 pages, 14 figures, A&A accepte
Interlayer hybridization and moir\'e superlattice minibands for electrons and excitons in heterobilayers of transition-metal dichalcogenides
Geometrical moir\'e patterns, generic for almost aligned bilayers of
two-dimensional (2D) crystals with similar lattice structure but slightly
different lattice constants, lead to zone folding and miniband formation for
electronic states. Here, we show that moir\'e superlattice (mSL) effects in
and
heterobilayers that feature alignment of the band edges are enhanced by
resonant interlayer hybridization, and anticipate similar features in twisted
homobilayers of TMDs, including examples of narrow minibands close to the
actual band edges. Such hybridization determines the optical activity of
interlayer excitons in transition-metal dichalcogenide (TMD) heterostructures,
as well as energy shifts in the exciton spectrum. We show that the resonantly
hybridized exciton (hX) energy should display a sharp modulation as a function
of the interlayer twist angle, accompanied by additional spectral features
caused by umklapp electron-photon interactions with the mSL. We analyze the
appearance of resonantly enhanced mSL features in absorption and emission of
light by the interlayer exciton hybridization with both intralayer A and B
excitons in , ,
, , and
.Comment: Final published version, with updated title and abstract, minor
corrections to equations, and 4 new figures adde
Real-time reverse transcription polymerase chain reaction development for rapid detection of Tomato brown rugose fruit virus and comparison with other techniques
Background: Tomato brown rugose fruit virus (ToBRFV) is a highly infectious tobamovirus that causes severe disease in tomato (Solanum lycopersicum L.) crops. In Italy, the first ToBRFV outbreak occurred in 2018 in several provinces of the Sicily region. ToBRFV outbreak represents a serious threat for tomato crops in Italy and the Mediterranean Basin. Methods: Molecular and biological characterisation of the Sicilian ToBRFV ToB-SIC01/19 isolate was performed, and a sensitive and specific Real-time RT-PCR TaqMan minor groove binder probe method was developed to detect ToBRFV in infected plants and seeds. Moreover, four different sample preparation procedures (immunocapture, total RNA extraction, direct crude extract and leaf-disk crude extract) were evaluated. Results: The Sicilian isolate ToB-SIC01/19 (6,391 nt) showed a strong sequence identity with the isolates TBRFV-P12-3H and TBRFV-P12-3G from Germany, Tom1-Jo from Jordan and TBRFV-IL from Israel. The ToB-SIC01/19 isolate was successfully transmitted by mechanical inoculations in S. lycopersicum L. and Capsicum annuum L., but no transmission occurred in S. melongena L. The developed real-time RT-PCR, based on the use of a primer set designed on conserved sequences in the open reading frames3, enabled a reliable quantitative detection. This method allowed clear discrimination of ToBRFV from other viruses belonging to the genus Tobamovirus, minimising false-negative results. Using immunocapture and total RNA extraction procedures, the real-time RT-PCR and end-point RT-PCR gave the same comparable results. Using direct crude extracts and leaf-disk crude extracts, the end-point RT-PCR was unable to provide a reliable result. This developed highly specific and sensitive real-time RT-PCR assay will be a particularly valuable tool for early ToBRFV diagnosis, optimising procedures in terms of costs and time
A numerical study of planar arrays of correlated spin islands
We present our analysis of a system of interacting islands of XY spins on a
triangular lattice that has been introduced a few years ago by Eley et al. to
account for the phenomenology in experiments on tunable arrays of proximity
coupled long superconductor-normal metal-superconductor junctions. The main
features of the model are the separation of a local and a global interaction
energy scale and the mesoscopic character of the spin islands. Upon lowering
the temperature the model undergoes two crossovers corresponding to an
increasing phase coherence on a single island and to the onset of global
coherence across the array; the latter is a thermodynamical phase transition in
the Ising universality class. The dependence of the second transition on the
island edge-to-edge spacing is related to the proximity-effect of the coupling
constant.Comment: 6 pages, 5 figures, accepted for publication in EPJ
An obscured AGN population hidden in the VIPERS galaxies: identification through spectral energy distribution decomposition
The detection of X-ray emission constitutes a reliable and efficient tool for
the selection of Active Galactic Nuclei (AGNs), although it may be biased
against the most heavily absorbed AGNs. Simple mid-IR broad-band selection
criteria identify a large number of luminous and absorbed AGNs, yet again host
contamination could lead to non-uniform and incomplete samples. Spectral Energy
Distribution (SED) decomposition is able to decouple the emission from the AGN
versus that from star-forming regions, revealing weaker AGN components. We aim
to identify the obscured AGN population in the VIPERS survey in the CFHTLS W1
field through SED modelling. We construct SEDs for 6,860 sources and identify
160 AGNs at a high confidence level using a Bayesian approach. Using optical
spectroscopy, we confirm the nature of ~85% of the AGNs. Our AGN sample is
highly complete (~92%) compared to mid-IR colour selected AGNs, including a
significant number of galaxy-dominated systems with lower luminosities. In
addition to the lack of X-ray emission (80%), the SED fitting results suggest
that the majority of the sources are obscured. We use a number of diagnostic
criteria in the optical, infrared and X-ray regime to verify these results.
Interestingly, only 35% of the most luminous mid-IR selected AGNs have X-ray
counterparts suggesting strong absorption. Our work emphasizes the importance
of using SED decomposition techniques to select a population of type II AGNs,
which may remain undetected by either X-ray or IR colour surveys.Comment: Accepted for publication in MNRAS in May 4, 2020. 18 figures, 3
tables
Spectroscopic Signatures of Electronic Excitations in Raman Scattering in Thin Films of Rhombohedral Graphite
Rhombohedral graphite features peculiar electronic properties, including
persistence of low-energy surface bands of a topological nature. Here, we study
the contribution of electron-hole excitations towards inelastic light
scattering in thin films of rhombohedral graphite. We show that, in contrast to
the featureless electron-hole contribution towards Raman spectrum of graphitic
films with Bernal stacking, the inelastic light scattering accompanied by
electron-hole excitations in crystals with rhombohedral stacking produces
distinct features in the Raman signal which can be used both to identify the
stacking and to determine the number of layers in the film.Comment: 15 pages in preprint format, 4 figures, accepted versio
Electronic Raman Scattering in Twistronic Few-Layer Graphene
We study electronic contribution to the Raman scattering signals of two-,
three- and four-layer graphene with layers at one of the interfaces twisted by
a small angle with respect to each other. We find that the Raman spectra of
these systems feature two peaks produced by van Hove singularities in moir\'{e}
minibands of twistronic graphene, one related to direct hybridization of Dirac
states, and the other resulting from band folding caused by moir\'{e}
superlattice. The positions of both peaks strongly depend on the twist angle,
so that their detection can be used for non-invasive characterization of the
twist, even in hBN-encapsulated structures.Comment: 7 pages (including 4 figures) + 10 pages (3 figures) supplemen
Estimating Photometric Redshifts for X-ray sources in the X-ATLAS field, using machine-learning techniques
We present photometric redshifts for 1,031 X-ray sources in the X-ATLAS
field, using the machine learning technique TPZ (Carrasco Kind & Brunner 2013).
X-ATLAS covers 7.1 deg2 observed with the XMM-Newton within the Science
Demonstration Phase (SDP) of the H-ATLAS field, making it one of the largest
contiguous areas of the sky with both XMMNewton and Herschel coverage. All of
the sources have available SDSS photometry while 810 have additionally mid-IR
and/or near-IR photometry. A spectroscopic sample of 5,157 sources primarily in
the XMM/XXL field, but also from several X-ray surveys and the SDSS DR13
redshift catalogue, is used for the training of the algorithm. Our analysis
reveals that the algorithm performs best when the sources are split, based on
their optical morphology, into point-like and extended sources. Optical
photometry alone is not enough for the estimation of accurate photometric
redshifts, but the results greatly improve when, at least, mid-IR photometry is
added in the training process. In particular, our measurements show that the
estimated photometric redshifts for the X-ray sources of the training sample,
have a normalized absolute median deviation, n_mad=0.06, and the percentage of
outliers, eta=10-14 percent, depending on whether the sources are extended or
point-like. Our final catalogue contains photometric redshifts for 933 out of
the 1,031 X-ray sources with a median redshift of 0.9.Comment: 10 pages, 13 figures, A&A accepte
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