141 research outputs found
First whole atmosphere night-time seeing measurements at Dome C, Antarctica
We report site testing results obtained in night-time during the polar autumn
and winter at Dome C. These results were collected during the first Concordia
winterover by A. Agabi. They are based upon seeing and isoplanatic angle
monitoring, as well as in-situ balloon measurements 2 of the refractive index
structure constant profiles Cn (h). Atmosphere is divided into two regions: (i)
a 36 m high surface layer responsible of 87% of the turbulence and (ii) a very
stable free atmosphere above with a median seeing of 0.36+-0.19 arcsec at an
elevation of h = 30 m. The median seeing measured with a DIMM placed on top of
a 8.5 m high tower is 1.3+-0.8 arcsec.Comment: accepted for publication in PASP (oct 2005
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
The X-CLASS - redMaPPer galaxy cluster comparison: I. Identification procedures
We performed a detailed and, for a large part interactive, analysis of the
matching output between the X-CLASS and redMaPPer cluster catalogues. The
overlap between the two catalogues has been accurately determined and possible
cluster positional errors were manually recovered. The final samples comprise
270 and 355 redMaPPer and X-CLASS clusters respectively. X-ray cluster matching
rates were analysed as a function of optical richness. In a second step, the
redMaPPer clusters were correlated with the entire X-ray catalogue, containing
point and uncharacterised sources (down to a few 10^{-15} erg s^{-1} cm^{-2} in
the [0.5-2] keV band). A stacking analysis was performed for the remaining
undetected optical clusters. Main results show that neither of the wavebands
misses any massive cluster (as coded by X-ray luminosity or optical richness).
After correcting for obvious pipeline short-comings (about 10% of the cases
both in optical and X-ray), ~50% of the redMaPPer (down to a richness of 20)
are found to coincide with an X-CLASS cluster; when considering X-ray sources
of any type, this fraction increases to ~ 80%; for the remaining objects, the
stacking analysis finds a weak signal within 0.5 Mpc around the cluster optical
centers. The fraction of clusters totally dominated by AGN-type emission
appears to be of the order of a few percent. Conversely ~ 40% of the X-CLASS
clusters are identified with a redMaPPer (down to a richness of 20) - part of
the non-matches being due to the fact that the X-CLASS sample extends further
out than redMaPPer (z<1 vs z<0.6); extending the correlation down to a richness
of 5, raises the matching rate to ~ 65%.Comment: 15 pages, 20 figures, 2 table
To determine the role and importance of marketing research in the development of tourist routes
The article examines the role and importance of marketing research in the development of tourist routes in our country
The XMM-LSS survey: the Class 1 cluster sample over the extended 11 deg and its spatial distribution
This paper presents 52 X-ray bright galaxy clusters selected within the 11
deg XMM-LSS survey. 51 of them have spectroscopic redshifts
(), one is identified at , and all together make
the high-purity "Class 1" (C1) cluster sample of the XMM-LSS, the highest
density sample of X-ray selected clusters with a monitored selection function.
Their X-ray fluxes, averaged gas temperatures (median keV),
luminosities (median ergs/s) and total mass
estimates (median ) are measured, adapting to
the specific signal-to-noise regime of XMM-LSS observations. The redshift
distribution of clusters shows a deficit of sources when compared to the
cosmological expectations, regardless of whether WMAP-9 or Planck-2013 CMB
parameters are assumed. This lack of sources is particularly noticeable at . However, after quantifying uncertainties due to small
number statistics and sample variance we are not able to put firm (i.e. ) constraints on the presence of a large void in the cluster
distribution. We work out alternative hypotheses and demonstrate that a
negative redshift evolution in the normalization of the relation
(with respect to a self-similar evolution) is a plausible explanation for the
observed deficit. We confirm this evolutionary trend by directly studying how
C1 clusters populate the space, properly accounting for selection
biases. We point out that a systematically evolving, unresolved, central
component in clusters and groups (AGN contamination or cool core) can impact
the classification as extended sources and be partly responsible for the
observed redshift distribution.[abridged]Comment: 33 pages, 21 figures, 3 tables ; accepted for publication in MNRA
The Optimal Gravitational Lens Telescope
Given an observed gravitational lens mirage produced by a foreground
deflector (cf. galaxy, quasar, cluster,...), it is possible via numerical lens
inversion to retrieve the real source image, taking full advantage of the
magnifying power of the cosmic lens. This has been achieved in the past for
several remarkable gravitational lens systems. Instead, we propose here to
invert an observed multiply imaged source directly at the telescope using an
ad-hoc optical instrument which is described in the present paper. Compared to
the previous method, this should allow one to detect fainter source features as
well as to use such an optimal gravitational lens telescope to explore even
fainter objects located behind and near the lens. Laboratory and numerical
experiments illustrate this new approach
Wind speed vertical distribution at Mt. Graham
The characterization of the wind speed vertical distribution V(h) is
fundamental for an astronomical site for many different reasons: (1) the wind
speed shear contributes to trigger optical turbulence in the whole troposphere,
(2) a few of the astroclimatic parameters such as the wavefront coherence time
(tau_0) depends directly on V(h), (3) the equivalent velocity V_0, controlling
the frequency at which the adaptive optics systems have to run to work
properly, depends on the vertical distribution of the wind speed and optical
turbulence. Also, a too strong wind speed near the ground can introduce
vibrations in the telescope structures. The wind speed at a precise pressure
(200 hPa) has frequently been used to retrieve indications concerning the tau_0
and the frequency limits imposed to all instrumentation based on adaptive
optics systems, but more recently it has been proved that V_200 (wind speed at
200 hPa) alone is not sufficient to provide exhaustive elements concerning this
topic and that the vertical distribution of the wind speed is necessary. In
this paper a complete characterization of the vertical distribution of wind
speed strength is done above Mt.Graham (Arizona, US), site of the Large
Binocular Telescope. We provide a climatological study extended over 10 years
using the operational analyses from the European Centre for Medium-Range
Weather Forecasts (ECMWF), we prove that this is representative of the wind
speed vertical distribution at Mt. Graham with exception of the boundary layer
and we prove that a mesoscale model can provide reliable nightly estimates of
V(h) above this astronomical site from the ground up to the top of the
atmosphere (~ 20 km).Comment: 12 pages, 9 figures (whereof 3 colour), accepted by MNRAS May 27,
201
The XXL Survey VIII: MUSE characterisation of intracluster light in a z0.53 cluster of galaxies
Within a cluster, gravitational effects can lead to the removal of stars from
their parent galaxies. Gas hydrodynamical effects can additionally strip gas
and dust from galaxies. The properties of the ICL can therefore help constrain
the physical processes at work in clusters by serving as a fossil record of the
interaction history. The present study is designed to characterise this ICL in
a ~10^14 M_odot and z~0.53 cluster of galaxies from imaging and spectroscopic
points of view. By applying a wavelet-based method to CFHT Megacam and WIRCAM
images, we detect significant quantities of diffuse light. These sources were
then spectroscopically characterised with MUSE. MUSE data were also used to
compute redshifts of 24 cluster galaxies and search for cluster substructures.
An atypically large amount of ICL has been detected in this cluster. Part of
the detected diffuse light has a very weak optical stellar component and
apparently consists mainly of gas emission, while other diffuse light sources
are clearly dominated by old stars. Furthermore, emission lines were detected
in several places of diffuse light. Our spectral analysis shows that this
emission likely originates from low-excitation parameter gas. The stellar
contribution to the ICL is about 2.3x10^9 yrs old even though the ICL is not
currently forming a large number of stars. On the other hand, the contribution
of the gas emission to the ICL in the optical is much greater than the stellar
contribution in some regions, but the gas density is likely too low to form
stars. These observations favour ram pressure stripping, turbulent viscous
stripping, or supernovae winds as the origin of the large amount of
intracluster light. Since the cluster appears not to be in a major merging
phase, we conclude that ram pressure stripping is the most plausible process
that generates the observed ICL sources.Comment: Accepted in A&A, english enhanced, figure location different than in
the A&A version due to different style files, shortened abstrac
The XXL Survey: XII. Optical spectroscopy of X-ray-selected clusters and the frequency of AGN in superclusters
This article belongs to the first series of XXL publications. It presents
multifibre spectroscopic observations of three 0.55 sq.deg. fields in the XXL
Survey, which were selected on the basis of their high density of
X-ray-detected clusters. The observations were obtained with the
AutoFib2+WYFFOS (AF2) wide-field fibre spectrograph mounted on the 4.2m William
Herschel Telescope. The paper first describes the scientific rationale, the
preparation, the data reduction, and the results of the observations, and then
presents a study of active galactic nuclei (AGN) within three superclusters. We
obtained redshifts for 455 galaxies in total, 56 of which are counterparts of
X-ray point-like sources. We were able to determine the redshift of the merging
supercluster XLSSC-e, which consists of six individual clusters at z~0.43, and
we confirmed the redshift of supercluster XLSSC-d at z~0.3. More importantly,
we discovered a new supercluster, XLSSC-f, that comprises three galaxy clusters
also at z~0.3. We find a significant 2D overdensity of X-ray point-like sources
only around the supercluster XLSSC-f. This result is also supported by the
spatial (3D) analysis of XLSSC-f, where we find four AGN with compatible
spectroscopic redshifts and possibly one more with compatible photometric
redshift. In addition, we find two AGN (3D analysis) at the redshift of
XLSSC-e, but no AGN in XLSSC-d. Comparing these findings with the optical
galaxy overdensity we conclude that the total number of AGN in the area of the
three superclusters significantly exceeds the field expectations. The
difference in the AGN frequency between the three superclusters cannot be
explained by the present study because of small number statistics. Further
analysis of a larger number of superclusters within the 50 sq. deg. of the XXL
is needed before any conclusions on the effect of the supercluster environment
on AGN can be reached.Comment: 11 pages, published by A&
The cosmological analysis of X-ray cluster surveys: II- Application of the CR-HR method to the XMM archive
We have processed 2774 high-galactic observations from the XMM archive (as of
May 2010) and extracted a serendipitous catalogue of some 850 clusters of
galaxies based on purely X-ray criteria, following the methodology developed
for the XMM-LSS survey. Restricting the sample to the highest signal-to-noise
objects (347 clusters), we perform a cosmological analysis using the X-ray
information only. The analysis consists in the modelling of the observed
colour-magnitude (CR-HR) diagram constructed from cluster instrumental
count-rates measured in the [0.5-2], [1-2] and [0.5-1] keV bands. A MCMC
procedure simultaneously fits the cosmological parameters, the evolution of the
cluster scaling laws and the selection effects. Our results are consistent with
the sigma_8 and Omega_m values obtained by WMAP-5 and point toward a negative
evolution of the cluster scaling relations with respect to the self-similar
expectation. We are further able to constrain the cluster fractional radius
xc0=r_c/r500c, to xc0=0.24 +/- 0.04. This study stresses again the critical
role of selection effects in deriving cluster scaling relations, even in the
local universe. Finally, we show that CR-HR method applied to the eRosita
all-sky survey - provided that cluster photometric redshifts are available -
will enable the determination of the equation of state of the dark energy at
the level of the DETF stage IV predictions; simultaneously, the evolution of
the cluster scaling-relations will be unambiguously determined. The XMM CLuster
Archive Super Survey (XCLASS) serendipitous cluster catalogue is available
online at: http://xmm-lss.in2p3.fr:8080/l4sdb/.Comment: 26 pages, 24 figures, 9 tables. Accepted for publication in MNRAS
(minor changes with respect to submitted version). The corresponding galaxy
cluster catalogue is available at http://xmm-lss.in2p3.fr:8080/l4sdb
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