139 research outputs found
Probing the Relation Between X-ray-Derived and Weak-Lensing-Derived Masses for Shear-Selected Galaxy Clusters: I. A781
We compare X-ray and weak-lensing masses for four galaxy clusters that
comprise the top-ranked shear-selected cluster system in the Deep Lens Survey.
The weak-lensing observations of this system, which is associated with A781,
are from the Kitt Peak Mayall 4-m telescope, and the X-ray observations are
from both Chandra and XMM-Newton. For a faithful comparison of masses, we adopt
the same matter density profile for each method, which we choose to be an NFW
profile. Since neither the X-ray nor weak-lensing data are deep enough to well
constrain both the NFW scale radius and central density, we estimate the scale
radius using a fitting function for the concentration derived from cosmological
hydrodynamic simulations and an X-ray estimate of the mass assuming
isothermality. We keep this scale radius in common for both X-ray and
weak-lensing profiles, and fit for the central density, which scales linearly
with mass. We find that for three of these clusters, there is agreement between
X-ray and weak-lensing NFW central densities, and thus masses. For the other
cluster, the X-ray central density is higher than that from weak-lensing by 2
sigma. X-ray images suggest that this cluster may be undergoing a merger with a
smaller cluster. This work serves as an additional step towards understanding
the possible biases in X-ray and weak-lensing cluster mass estimation methods.
Such understanding is vital to efforts to constrain cosmology using X-ray or
weak-lensing cluster surveys to trace the growth of structure over cosmic time.Comment: 14 pages, 7 figures, matches version in Ap
The Shapley super-cluster. New X-ray detections and mass distribution
The largest and the deepest super-structure known today is the Shapley
super-cluster. This is the sky area with the highest over-density of galaxy
clusters and therefore also an ideal region to test the effects of a high
density environment on galaxies and on clusters. We performed an X-ray survey
of a wide region surrounding the Shapley super-structure. Additionally to
previously known super-cluster X-ray members, we identified diffuse X-ray
emission from 35 cluster candidates without previous X-ray detection. 21 of
them were previously known, optically selected super-cluster members, while the
other candidates had not been previously detected in any wavelength range.
Optical follow-up observations revealed that at least four of these new
candidates also have optical cluster counterparts. The super-cluster shows a
slightly flattened and elongated morphology. Clusters outside the central dense
core are preferentially located in four perpendicular filaments in a similar
way to what is seen in simulations of Large Scale Structure. We measure the
cluster number density in the region to be more than one order of magnitude
higher than the mean density of rich Abell clusters previously observed at
similar Galactic latitudes; this over-density, in the super-cluster outskirts,
is mainly due to an excess of low X-ray luminous clusters (with respect to an
average population), which leads us to think that the whole region is still
accreting low luminosity, small objects from the outskirts. Pushing our total
X-ray mass estimate to fainter clusters would drastically increase the total
super-cluster mass measure, because of the presence of the rich X-ray low
luminosity population.Comment: 27 pages; accepted for publication in A&A. A version of the paper
with higher resolution images can be downloaded at:
http://people.na.infn.it/~betty/publications_files/Shapley.ps.g
Introducing BAX: a database for X-ray clusters and groups of galaxies
We present BAX, Base de Donnees Amas de Galaxies X
(http://webast.ast.obs-mip.fr/bax), a multi-wavelength database dedicated to
X-ray clusters and groups of galaxies allowing detailed information retrieval.
BAX is designed to support astronomical research by providing access to
published measurements of the main physical quantities and to the related
bibliographic references: basic data stored in the database are cluster/group
identifiers, equatorial coordinates, redshift, flux, X-ray luminosity (in the
ROSAT band) and temperature, and links to additional linked parameters (in
X-rays, such as spatial profile parameters, as well as SZ parameters of the hot
gas, lensing measurements,and data at other wavelengths, such as optical and
radio). The clusters and groups in BAX can be queried by the basic parameters
as well as the linked parameters or combinations of these. We expect BAX to
become an important tool for the astronomical community. BAX will optimize
various aspects of the scientific analysis of X-ray clusters and groups of
galaxies, from proposal planning to data collection, interpretation and
publication, from both ground based facilities like MEGACAM (CFHT), VIRMOS
(VLT) and space missions like XMM-Newton, Chandra and Planck.Comment: Accepted for publication in Astronomy and Astrophysics Journal.
Contains 4 pages and 1 figur
Elucidation of the Average Molecular Structure of Argentinian Asphaltenes
Petroleum asphaltenes were separated from three different Argentinian crude oils. The asphaltene fractions were extracted by precipitation employing n-pentane and n-heptane solvents, and the coprecipitated resins were removed via Soxhlet extraction. The asphaltenes were characterized by elemental analysis, thermogravimetric analysis, laser desorption ionization mass spectrometry, Fourier-transform infrared spectroscopy, proton nuclear magnetic resonance, powder X-ray diffraction, and Raman spectroscopy. It was found that the asphaltene fractions present both a higher content of heteroatoms and a major degree of aromaticity, when n-heptane is employed. Average structural parameters were obtained by a comprehensive analysis of the experimental data, including those describing the central polycyclic aromatic hydrocarbon (PAH) cores and lateral chains. Thus, a hypothetical average molecular structure is proposed for the Argentinian asphaltenes. The average model molecules have a nucleus of PAHs arranged as pericondensed systems of 4-6 fused aromatic rings, with naphthenic groups and/or alkyl chains of 5-10 carbon long attached.Fil: Bava, Yanina BelĂ©n. Facultad de Ciencias Exactas, Universidad Nacional de la Plata; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - La Plata. Centro de QuĂmica InorgĂĄnica "Dr. Pedro J. Aymonino". Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Centro de QuĂmica InorgĂĄnica "Dr. Pedro J. Aymonino"; ArgentinaFil: Gerones, Mariana. Facultad de Ciencias Exactas, Universidad Nacional de la Plata; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - La Plata. Centro de QuĂmica InorgĂĄnica "Dr. Pedro J. Aymonino". Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Centro de QuĂmica InorgĂĄnica "Dr. Pedro J. Aymonino"; ArgentinaFil: Buceta, David. Universidad de Santiago de Compostela; EspañaFil: De La Iglesia RodrĂguez, DarĂo. Universidad de Santiago de Compostela; EspañaFil: LĂłpez-Quintela, M. Arturo. Universidad de Santiago de Compostela; EspañaFil: Erben, Mauricio Federico. Facultad de Ciencias Exactas, Universidad Nacional de la Plata; Argentina. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Centro CientĂfico TecnolĂłgico Conicet - La Plata. Centro de QuĂmica InorgĂĄnica "Dr. Pedro J. Aymonino". Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Centro de QuĂmica InorgĂĄnica "Dr. Pedro J. Aymonino"; Argentin
Stochastic bias of colour-selected BAO tracers by joint clustering-weak lensing analysis
The baryon acoustic oscillation (BAO) feature in the two-point correlation
function of galaxies supplies a standard ruler to probe the expansion history
of the Universe. We study here several galaxy selection schemes, aiming at
building an emission-line galaxy (ELG) sample in the redshift range
, that would be suitable for future BAO studies, providing a highly
biased galaxy sample. We analyse the angular galaxy clustering of galaxy
selections at the redshifts 0.5, 0.7, 0.8, 1 and 1.2 and we combine this
analysis with a halo occupation distribution (HOD) model to derive the
properties of the haloes these galaxies inhabit, in particular the galaxy bias
on large scales. We also perform a weak lensing analysis (aperture statistics)
to extract the galaxy bias and the cross-correlation coefficient and compare to
the HOD prediction.
We apply this analysis on a data set composed of the photometry of the deep
co-addition on Sloan Digital Sky Survey (SDSS) Stripe 82 (225 deg), of
Canda-France-Hawai Telescope/Stripe 82 deep \emph{i}-band weak lensing survey
and of the {\it Wide-Field Infrared Survey Explorer}infrared photometric band
W1.
The analysis on the SDSS-III/constant mass galaxies selection at is
in agreement with previous studies on the tracer, moreover we measure its
cross-correlation coefficient . For the higher redshift bins, we
confirm the trends that the brightest galaxy populations selected are strongly
biased (), but we are limited by current data sets depth to derive
precise values of the galaxy bias. A survey using such tracers of the mass
field will guarantee a high significance detection of the BAO.Comment: 17 pages, 15 figures, submitted to MNRA
Teaching earth science students to recognize communicative intent in media headlines: clickbait phenomenon
This paper examines ways of teaching Earth science students techniques to recognize manipulative clickbait in the online versions of American newspapers. The study presents an analysis of headlines in the online versions of the newspaper aiming to determine the specificities of the use of clickbait and to further classify the techniques through which it is employed. The analyzed data was collected from the Sports and Business sections of the 2021 online issues of the New York Times and the Washington Post. The frequency of clickbait use was found in each of the newspapers in general and in each of the studies section in particular. The analysis resulted in the classification of the techniques of achieving the clickbait effect. The individual characteristics of the journalistsâ styles of the newspapers under study was further investigated. The quantitative analysis revealed varying amounts of clickbait in the headlines of the online newspapers
Weighing the Giants - I. Weak-lensing masses for 51 massive galaxy clusters: project overview, data analysis methods and cluster images
This is the first in a series of papers in which we measure accurate
weak-lensing masses for 51 of the most X-ray luminous galaxy clusters known at
redshifts 0.15<z<0.7, in order to calibrate X-ray and other mass proxies for
cosmological cluster experiments. The primary aim is to improve the absolute
mass calibration of cluster observables, currently the dominant systematic
uncertainty for cluster count experiments. Key elements of this work are the
rigorous quantification of systematic uncertainties, high-quality data
reduction and photometric calibration, and the "blind" nature of the analysis
to avoid confirmation bias. Our target clusters are drawn from RASS X-ray
catalogs, and provide a versatile calibration sample for many aspects of
cluster cosmology. We have acquired wide-field, high-quality imaging using the
Subaru and CFHT telescopes for all 51 clusters, in at least three bands per
cluster. For a subset of 27 clusters, we have data in at least five bands,
allowing accurate photo-z estimates of lensed galaxies. In this paper, we
describe the cluster sample and observations, and detail the processing of the
SuprimeCam data to yield high-quality images suitable for robust weak-lensing
shape measurements and precision photometry. For each cluster, we present
wide-field color optical images and maps of the weak-lensing mass distribution,
the optical light distribution, and the X-ray emission, providing insights into
the large-scale structure in which the clusters are embedded. We measure the
offsets between X-ray centroids and Brightest Cluster Galaxies in the clusters,
finding these to be small in general, with a median of 20kpc. For offsets
<100kpc, weak-lensing mass measurements centered on the BCGs agree well with
values determined relative to the X-ray centroids; miscentering is therefore
not a significant source of systematic uncertainty for our mass measurements.
[abridged]Comment: 26 pages, 19 figures (Appendix C not included). Accepted after minor
revisio
Bayesian analysis of weak gravitational lensing and Sunyaev-Zel'dovich data for six galaxy clusters
We present an analysis of observations made with the Arcminute Microkelvin
Imager (AMI) and the Canada-France-Hawaii Telescope (CFHT) of six galaxy
clusters in a redshift range of 0.16--0.41. The cluster gas is modelled using
the Sunyaev--Zel'dovich (SZ) data provided by AMI, while the total mass is
modelled using the lensing data from the CFHT. In this paper, we: i) find very
good agreement between SZ measurements (assuming large-scale virialisation and
a gas-fraction prior) and lensing measurements of the total cluster masses out
to r_200; ii) perform the first multiple-component weak-lensing analysis of
A115; iii) confirm the unusual separation between the gas and mass components
in A1914; iv) jointly analyse the SZ and lensing data for the relaxed cluster
A611, confirming our use of a simulation-derived mass-temperature relation for
parameterizing measurements of the SZ effect.Comment: 22 pages, 12 figures, 12 tables, published by MNRA
Probing galaxy bias and intergalactic gas pressure with KiDS Galaxies-tSZ-CMB lensing cross-correlations
We constrain the redshift dependence of gas pressure bias (bias-weighted average electron pressure), which
characterises the thermodynamics of intergalactic gas, through a combination of
cross-correlations between galaxy positions and the thermal Sunyaev-Zeldovich
(tSZ) effect, as well as galaxy positions and the gravitational lensing of the
cosmic microwave background (CMB). The galaxy sample is from the fourth data
release of the Kilo-Degree Survey (KiDS). The tSZ map and the CMB lensing
map are from the {\textit{Planck}} 2015 and 2018 data releases, respectively.
The measurements are performed in five redshift bins with . With
these measurements, combining galaxy-tSZ and galaxy-CMB lensing
cross-correlations allows us to break the degeneracy between galaxy bias and
gas pressure bias, and hence constrain them simultaneously. In all redshift
bins, the best-fit values of \bpe are at a level of and increase slightly with redshift. The galaxy bias is
consistent with unity in all the redshift bins. Our results are not sensitive
to the non-linear details of the cross-correlation, which are smoothed out by
the {\textit{Planck}} beam. Our measurements are in agreement with previous
measurements as well as with theoretical predictions. We also show that our
conclusions are not changed when CMB lensing is replaced by galaxy lensing,
which shows the consistency of the two lensing signals despite their radically
different redshift ranges. This study demonstrates the feasibility of using CMB
lensing to calibrate the galaxy distribution such that the galaxy distribution
can be used as a mass proxy without relying on the precise knowledge of the
matter distribution.Comment: 20 pages, 14 figures, 3 tables, accepted for publication on Astronomy
& Astrophysic
A Public, K-Selected, Optical-to-Near-Infrared Catalog of the Extended Chandra Deep Field South (ECDFS) from the MUltiwavelength Survey by Yale-Chile (MUSYC)
We present a new K-selected, optical-to-near-infrared photometric catalog of
the Extended Chandra Deep Field South (ECDFS), making it publicly available to
the astronomical community. The dataset is founded on publicly available
imaging, supplemented by original zJK imaging data obtained as part of the
MUltiwavelength Survey by Yale-Chile (MUSYC). The final photometric catalog
consists of photometry derived from nine band U-K imaging covering the full
0.5x0.5 sq. deg. of the ECDFS, plus H band data for approximately 80% of the
field. The 5sigma flux limit for point-sources is K = 22.0 (AB). This is also
the nominal completeness and reliability limit of the catalog: the empirical
completeness for 21.75 < K < 22.00 is 85+%. We have verified the quality of the
catalog through both internal consistency checks, and comparisons to other
existing and publicly available catalogs. As well as the photometric catalog,
we also present catalogs of photometric redshifts and restframe photometry
derived from the ten band photometry. We have collected robust spectroscopic
redshift determinations from published sources for 1966 galaxies in the
catalog. Based on these sources, we have achieved a (1sigma) photometric
redshift accuracy of Dz/(1+z) = 0.036, with an outlier fraction of 7.8%. Most
of these outliers are X-ray sources. Finally, we describe and release a utility
for interpolating restframe photometry from observed SEDs, dubbed InterRest.
Particularly in concert with the wealth of already publicly available data in
the ECDFS, this new MUSYC catalog provides an excellent resource for studying
the changing properties of the massive galaxy population at z < 2. (Abridged)Comment: Re-submitted to ApJSS after a first referee report. 27 pages, 17
figures. MUSYC data is freely available from http://astro.yale.edu/MUSYC .
Links to phot-z and restframe photometry catalogs, as well as to InterRest
access and documentation, including a full walkthrough, can be found at
http://www.strw.leidenuniv.nl/~ent
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