112 research outputs found
Predicted multiply-imaged X-ray AGNs in the XXL survey
We estimate the incidence of multiply-imaged AGNs among the optical
counterparts of X-ray selected point-like sources in the XXL field. We also
derive the expected statistical properties of this sample, such as the redshift
distribution of the lensed sources and of the deflectors that lead to the
formation of multiple images, modelling the deflectors using both spherical
(SIS) and ellipsoidal (SIE) singular isothermal mass distributions. We further
assume that the XXL survey sample has the same overall properties as the
smaller XMM-COSMOS sample restricted to the same flux limits and taking into
account the detection probability of the XXL survey. Among the X-ray sources
with a flux in the [0.5-2] keV band larger than 3.0x10 erg cm
s and with optical counterparts brighter than an r-band magnitude of 25,
we expect ~20 multiply-imaged sources. Out of these, ~16 should be detected if
the search is made among the seeing-limited images of the X-ray AGN optical
counterparts and only one of them should be composed of more than two lensed
images. Finally, we study the impact of the cosmological model on the expected
fraction of lensed sources.Comment: 15 pages, 7 figures, 1 table, accepted for publication in MNRA
Search for gravitational lens candidates in the XMM-LSS/CFHTLS common field
Our aim was to identify gravitational lens candidates among some 5500 optical
counterparts of the X-ray point-like sources in the medium-deep ~11 sq. deg.
XMM-LSS survey. We have visually inspected the optical counterparts of each
QSOs/AGN using CFHTLS T006 images. We have selected compact pairs and groups of
sources which could be multiply imaged QSO/AGN. We have measured the colors and
characterized the morphological types of the selected sources using the
multiple PSF fitting technique. We found three good gravitational lens
candidates: J021511.4-034306, J022234.3-031616 and J022607.0-040301 which
consist of pairs of point-like sources having similar colors. On the basis of a
color-color diagram and X-ray properties we could verify that all these sources
are good QSO/AGN candidates rather than stars. Additional secondary
gravitational lens candidates are also reported.Comment: 6 pages, 3 figures, 1 table, Accepted for publication in MNRA
Machine learning technique for morphological classification of galaxies at z<0.1 from the SDSS
Methods. We used different galaxy classification techniques: human labeling,
multi-photometry diagrams, Naive Bayes, Logistic Regression, Support Vector
Machine, Random Forest, k-Nearest Neighbors, and k-fold validation. Results. We
present results of a binary automated morphological classification of galaxies
conducted by human labeling, multiphotometry, and supervised Machine Learning
methods. We applied its to the sample of galaxies from the SDSS DR9 with
redshifts of 0.02 < z < 0.1 and absolute stellar magnitudes of 24m < Mr <
19.4m. To study the classifier, we used absolute magnitudes: Mu, Mg, Mr , Mi,
Mz, Mu-Mr , Mg-Mi, Mu-Mg, Mr-Mz, and inverse concentration index to the center
R50/R90. Using the Support vector machine classifier and the data on color
indices, absolute magnitudes, inverse concentration index of galaxies with
visual morphological types, we were able to classify 316 031 galaxies from the
SDSS DR9 with unknown morphological types. Conclusions. The methods of Support
Vector Machine and Random Forest with Scikit-learn machine learning in Python
provide the highest accuracy for the binary galaxy morphological
classification: 96.4% correctly classified (96.1% early E and 96.9% late L
types) and 95.5% correctly classified (96.7% early E and 92.8% late L types),
respectively. Applying the Support Vector Machine for the sample of 316 031
galaxies from the SDSS DR9 at z < 0.1, we found 141 211 E and 174 820 L types
among them.Comment: 10 pages, 5 figures. The presentation of these results was given
during the EWASS-2017, Symposium "Astroinformatics: From Big Data to
Understanding the Universe at Large". It is vailable through
\url{http://space.asu.cas.cz/~ewass17-soc/Presentations/S14/Dobrycheva_987.pdf
Machine-learning computation of distance modulus for local galaxies
Quickly growing computing facilities and an increasing number of
extragalactic observations encourage the application of data-driven approaches
to uncover hidden relations from astronomical data. In this work we raise the
problem of distance reconstruction for a large number of galaxies from
available extensive observations. We propose a new data-driven approach for
computing distance moduli for local galaxies based on the machine-learning
regression as an alternative to physically oriented methods. We use key
observable parameters for a large number of galaxies as input explanatory
variables for training: magnitudes in U, B, I, and K bands, corresponding
colour indices, surface brightness, angular size, radial velocity, and
coordinates. We performed detailed tests of the five machine-learning
regression techniques for inference of : linear, polynomial, k-nearest
neighbours, gradient boosting, and artificial neural network regression. As a
test set we selected 91 760 galaxies at from the NASA/IPAC
extragalactic database with distance moduli measured by different independent
redshift methods. We find that the most effective and precise is the neural
network regression model with two hidden layers. The obtained root-mean-square
error of 0.35 mag, which corresponds to a relative error of 16\%, does not
depend on the distance to galaxy and is comparable with methods based on the
Tully-Fisher and Fundamental Plane relations. The proposed model shows a 0.44
mag (20\%) error in the case of spectroscopic redshift absence and is
complementary to existing photometric redshift methodologies. Our approach has
great potential for obtaining distance moduli for around 250 000 galaxies at
for which the above-mentioned parameters are already observed.Comment: 8 pages, 5 figures, Accepted for publication in A&
X-ray AGN in the XMM-LSS galaxy clusters: no evidence of AGN suppression
We present a study of the overdensity of X-ray selected AGN in 33 galaxy
clusters in the XMM-LSS field, up to redhift z=1.05. Previous studies have
shown that the presence of X-ray selected AGN in rich galaxy clusters is
suppressed. In the current study we investigate the occurrence of X-ray
selected AGN in low and moderate X-ray luminosity galaxy clusters. Due to the
wide contiguous XMM-LSS survey area we are able to extend the study to the
cluster outskirts. We therefore determine the projected overdensity of X-ray
point-like sources out to 6r_{500} radius. To provide robust statistical
results we also use a stacking analysis of the cluster projected overdensities.
We investigate whether the observed X-ray overdensities are to be expected by
estimating also the corresponding optical galaxy overdensities. We find a
positive X-ray projected overdensity at the first radial bin, which is however
of the same amplitude as that of optical galaxies. Therefore, no suppression of
X-ray AGN activity with respect to the field is found, implying that the
mechanisms responsible for the suppression are not so effective in lower
density environments. After a drop to roughly the background level between 2
and 3r_{500}, the X-ray overdensity exhibits a rise at larger radii,
significantly larger than the corresponding optical overdensity. Finally, using
redshift information of all optical counterparts, we derive the spatial
overdensity profile of the clusters. We find that the agreement between X-ray
and optical overdensities in the first radial bin is also suggested in the
3-dimensional analysis. However, we argue that the X-ray overdensity "bump" at
larger radial distance is probably a result of flux boosting by gravitational
lensing of background QSOs. For high redshift clusters an enhancement of X-ray
AGN activity in their outskirts is still possible.Comment: 16 pages. Accepted for publication in A&
Physical properties of the planetary systems WASP-45 and WASP-46 from simultaneous multiband photometry
Accurate measurements of the physical characteristics of a large number of exoplanets are useful to strongly constrain theoretical models of planet formation and evolution, which lead to the large variety of exoplanets and planetary-system configurations that have been observed. We present a study of the planetary systems WASP-45 and WASP-46, both composed of a main-sequence star and a close-in hot Jupiter, based on 29 new high-quality light curves of transits events. In particular, one transit of WASP-45 b and four of WASP-46 b were simultaneously observed in four optical filters, while one transit of WASP-46 b was observed with the NTT obtaining a precision of 0.30 mmag with a cadence of roughly 3 min. We also obtained five new spectra of WASP-45 with the FEROS spectrograph. We improved by a factor of 4 the measurement of the radius of the planet WASP-45 b, and found that WASP-46 b is slightly less massive and smaller than previously reported. Both planets now have a more accurate measurement of the density (0.959 ± 0.077 ρ_(Jup) instead of 0.64 ± 0.30 ρ_(Jup) for WASP-45 b, and 1.103 ± 0.052 ρ_(Jup) instead of 0.94 ± 0.11 ρ_(Jup) for WASP-46 b). We tentatively detected radius variations with wavelength for both planets, in particular in the case of WASP-45 b we found a slightly larger absorption in the redder bands than in the bluer ones. No hints for the presence of an additional planetary companion in the two systems were found either from the photometric or radial velocity measurements
The distribution of dark matter and intracluster gas in galaxy clusters
We present the temperature radial profiles of intracluster gas, and the radial profiles of density and mass for dark matter and intracluster gas for five galaxy clusters: Abell 1413, Abell 1204, Abell 2744, Abell 223 and CL 0024+17 observed by Chandra X-ray Observatory. These profiles were obtained based on the well-established fact, that the X-ray observed surface brightness of clusters are described well with the Navarro-Frenk-White density profile of the underlying dark matter distribution. We have found that density and mass profiles for all considered clusters have the same shape. Temperatures, masses and densities of these clusters lie within the ranges 5−10 keV, ∼ 10¹⁴ − 10¹⁵ Mꙩ and ∼ 10⁻²³ − 10⁻²⁵ kg/m3 respectively. We also determined the values of R₂₀₀ and M₂₀₀ for the clusters and estimated the fraction of gas and dark matter in total mass of each cluster to be ∼ 10 − 20% and ∼ 80 − 90% respectively
Chandra observations of ten galaxy clusters
In the present study the X-ray properties of 10 galaxy clusters (CL0024+17, RXJ1347.5+1145, A223, A521, A611, A697, A907, A1204, A1413 and A2744) are analysed using the archival X-ray data of the Chandra observatory. The average temperature of each cluster is estimated to be ∼ 4 − 10 keV, and the radial temperature profiles are reconstructed. Using the Navarro-Frenk-White (NFW) density pro le of the dark matter the density and mass
profiles for the dark matter and the hot diffuse gas, and also the total mass profiles are derived. The typical size of galaxy clusters and the density of the dark matter halo are estimated to be ∼ 0.1−2 Mpc and ∼ 10⁻²²−10⁻²⁴ kg/m³, respectively. The fraction of each component in the total cluster mass for the whole sample is found to be ∼ 80-90% for dark matter and ∼ 10 − 20% for intracluster gas, respectively
Gamma-ray induced cascades and magnetic fields in intergalactic medium
We present the results of Monte-Carlo simulations of three-dimensional
electromagnetic cascade initiated by interactions of the multi-TeV gamma-rays
with the cosmological infrared/optical photon background in the intergalactic
medium. Secondary electrons in the cascade are deflected by the intergalactic
magnetic fields before they scatter on CMB photons. This leads to extended
0.1-10 degree scale emission at multi-GeV and TeV energies around extragalactic
sources of very-high-energy gamma-rays. The morphology of the extended emission
depends, in general, on the properties of magnetic fields in the intergalactic
medium. Using Monte-Carlo simulated data sets, we demonstrate that the decrease
of the size of extended source with the increase of energy allows to measure
weak magnetic fields with magnitudes in the range from < 1e-16 G to 1e-12 G if
they exist in the voids of the Large Scale Structure.Comment: 11 pages, 8 figure
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