164 research outputs found
Reconstructing the projected gravitational potential of Abell 1689 from X-ray measurements
Context. Galaxy clusters can be used as cosmological probes, but to this end,
they need to be thoroughly understood. Combining all cluster observables in a
consistent way will help us to understand their global properties and their
internal structure. Aims. We provide proof of the concept that the projected
gravitational potential of galaxy clusters can directly be reconstructed from
X-ray observations. We also show that this joint analysis can be used to
locally test the validity of the equilibrium assumptions in galaxy clusters.
Methods. We used a newly developed reconstruction method, based on
Richardson-Lucy deprojection, that allows reconstructing projected
gravitational potentials of galaxy clusters directly from X-ray observations.
We applied this algorithm to the well-studied cluster Abell 1689 and compared
the gravitational potential reconstructed from X-ray observables to the
potential obtained from gravitational lensing measurements. [...] Results.
Assuming spherical symmetry and hydrostatic equilibrium, the potentials
recovered from gravitational lensing and from X-ray emission agree very well
beyond 500 kpc. Owing to the fact that the Richardson-Lucy deprojection
algorithm allows deprojecting each line of sight independently, this result may
indicate that non-gravitational effects and/or asphericity are strong in the
central regions of the clusters. Conclusions. We demonstrate the robustness of
the potential reconstruction method based on the Richardson-Lucy deprojection
algorithm and show that gravitational lensing and X-ray emission lead to
consistent gravitational potentials. Our results illustrate the power of
combining galaxy-cluster observables in a single, non-parametric, joint
reconstruction of consistent cluster potentials that can be used to locally
constrain the physical state of the gas.Comment: 8 pages, 4 figures. Accepted in A&
Little evidence for entropy and energy excess beyond - An end to ICM preheating?
Non-gravitational feedback affects the nature of the intra-cluster medium
(ICM). X-ray cooling of the ICM and in situ energy feedback from AGN's and SNe
as well as {\it preheating} of the gas at epochs preceding the formation of
clusters are proposed mechanisms for such feedback. While cooling and AGN
feedbacks are dominant in cluster cores, the signatures of a preheated ICM are
expected to be present even at large radii. To estimate the degree of
preheating, with minimum confusion from AGN feedback/cooling, we study the
excess entropy and non-gravitational energy profiles upto for a
sample of 17 galaxy clusters using joint data sets of {\it Planck} SZ pressure
and {\it ROSAT/PSPC} gas density profiles. The canonical value of preheating
entropy floor of keV cm, needed in order to match cluster
scalings, is ruled out at . We also show that the feedback
energy of 1 keV/particle is ruled out at 5.2 beyond . Our
analysis takes both non-thermal pressure and clumping into account which can be
important in outer regions. Our results based on the direct probe of the ICM in
the outermost regions do not support any significant preheating.Comment: 6 pages, 4 figures, 1 table, Accepted in MNRAS Letter
Excess entropy and energy feedback from within cluster cores up to r
We estimate the "non-gravitational" entropy-injection profiles, ,
and the resultant energy feedback profiles, , of the intracluster
medium for 17 clusters using their Planck SZ and ROSAT X-Ray observations,
spanning a large radial range from up to . The feedback
profiles are estimated by comparing the observed entropy, at fixed gas mass
shells, with theoretical entropy profiles predicted from non-radiative
hydrodynamic simulations. We include non-thermal pressure and gas clumping in
our analysis. The inclusion of non-thermal pressure and clumping results in
changing the estimates for and by 10\%-20\%. When
clumpiness is not considered it leads to an under-estimation of keV cm at and keV cm at
. On the other hand, neglecting non-thermal pressure results in an
over-estimation of keV cm at and
under-estimation of keV cm at . For the
estimated feedback energy, we find that ignoring clumping leads to an
under-estimation of energy per particle keV at and
keV at . Similarly, neglect of the non-thermal
pressure results in an over-estimation of keV at
and under-estimation of keV at . We find entropy
floor of keV cm is ruled out at
throughout the entire radial range and keV at more than
3 beyond , strongly constraining ICM pre-heating scenarios. We
also demonstrate robustness of results w.r.t sample selection, X-Ray analysis
procedures, entropy modeling etc.Comment: 17 pages, 15 figures, 5 tables, Accepted in MNRA
ALMA-SZ Detection of a Galaxy Cluster Merger Shock at Half the Age of the Universe
We present ALMA measurements of a merger shock using the thermal
Sunyaev-Zel'dovich (SZ) effect signal, at the location of a radio relic in the
famous El Gordo galaxy cluster at . Multi-wavelength analysis in
combination with the archival Chandra data and a high-resolution radio image
provides a consistent picture of the thermal and non-thermal signal variation
across the shock front and helps to put robust constraints on the shock Mach
number as well as the relic magnetic field. We employ a Bayesian analysis
technique for modeling the SZ and X-ray data self-consistently, illustrating
respective parameter degeneracies. Combined results indicate a shock with Mach
number , which in turn suggests a high value of
the magnetic field (of the order of G) to account for the observed
relic width at 2 GHz. At roughly half the current age of the universe, this is
the highest-redshift direct detection of a cluster shock to date, and one of
the first instances of an ALMA-SZ observation in a galaxy cluster. It shows the
tremendous potential for future ALMA-SZ observations to detect merger shocks
and other cluster substructures out to the highest redshifts.Comment: Matched to the ApJL published version (2016 September 22), minor
grammar and typo fixe
The Physics of Galaxy Cluster Outskirts
As the largest virialized structures in the universe, galaxy clusters
continue to grow and accrete matter from the cosmic web. Due to the low gas
density in the outskirts of clusters, measurements are very challenging,
requiring extremely sensitive telescopes across the entire electromagnetic
spectrum. Observations using X-rays, the Sunyaev-Zeldovich effect, and weak
lensing and galaxy distributions from the optical band, have over the last
decade helped to unravel this exciting new frontier of cluster astrophysics,
where the infall and virialization of matter takes place. Here, we review the
current state of the art in our observational and theoretical understanding of
cluster outskirts, and discuss future prospects for exploration using newly
planned and proposed observatories.Comment: 56 pages. Review paper. Published in Space Science Review
Extending Tables with Data from over a Million Websites
Abstract. This Big Data Track submission demonstrates how the BTC 2014 dataset, Microdata annotations from thousands of websites, as well as millions of HTML tables are used to extend local tables with additional columns. Ta-ble extension is a useful operation within a wide range of application scenarios: Imagine you are an analyst having a local table describing companies and you want to extend this table with the headquarter of each company. Or imagine you are a film enthusiast and want to extend a table describing films with attributes like director, genre, and release date of each film. The Mannheim Search Joins Engine automatically performs such table extension operations based on a large data corpus gathered from over a million websites that publish structured data in various formats. Given a local table, the Mannheim Search Joins Engine searches the corpus for additional data describing the entities of the input table. The dis-covered data are then joined with the local table and their content is consolidated using schema matching and data fusion methods. As result, the user is presented with an extended table and given the opportunity to examine the provenance o
Investigating the turbulent hot gas in X-COP galaxy clusters
Turbulent processes at work in the intracluster medium perturb this
environment, displacing gas, and creating local density fluctuations that can
be quantified via X-ray surface brightness fluctuation analyses. Improved
knowledge of these phenomena would allow for a better determination of the mass
of galaxy clusters, as well as a better understanding of their dynamic
assembly. In this work, we aim to set constraints on the structure of
turbulence using X-ray surface brightness fluctuations. We seek to consider the
stochastic nature of this observable and to constrain the structure of the
underlying power spectrum. We propose a new Bayesian approach, relying on
simulation-based inference to account for the whole error budget. We used the
X-COP cluster sample to individually constrain the power spectrum in four
regions and within . We spread the analysis on the 12 systems to
alleviate the sample variance. We then interpreted the density fluctuations as
the result of either gas clumping or turbulence. For each cluster considered
individually, the normalisation of density fluctuations correlates positively
with the Zernike moment and centroid shift, but negatively with the
concentration and the Gini coefficient. The spectral index within and
evaluated over all clusters is consistent with a Kolmogorov cascade. The
normalisation of density fluctuations, when interpreted in terms of clumping,
is consistent within with the literature results and numerical
simulations; however, it is higher between 0.5 and . Conversely,
when interpreted on the basis of turbulence, we deduce a non-thermal pressure
profile that is lower than the predictions of the simulations within 0.5
, but still in agreement in the outer regions. We explain these
results by the presence of central structural residues that are remnants of the
dynamic assembly of the clusters.Comment: Accepted for publication in A&A. Abstract slightly abridged for arXi
Allele-specific endogenous tagging and quantitative analysis of β-catenin in colorectal cancer cells
Wnt signaling plays important roles in development, homeostasis, and tumorigenesis. Mutations in β-catenin that activate Wnt signaling have been found in colorectal and hepatocellular carcinomas. However, the dynamics of wild-type and mutant forms of β-catenin are not fully understood. Here, we genome-engineered fluorescently tagged alleles of endogenous β-catenin in a colorectal cancer cell line. Wild-type and oncogenic mutant alleles were tagged with different fluorescent proteins, enabling the analysis of both variants in the same cell. We analyzed the properties of both β-catenin alleles using immunoprecipitation, immunofluorescence, and fluorescence correlation spectroscopy approaches, revealing distinctly different biophysical properties. In addition, activation of Wnt signaling by treatment with a GSK3β inhibitor or a truncating APC mutation modulated the wild-type allele to mimic the properties of the mutant β-catenin allele. The one-step tagging strategy demonstrates how genome engineering can be employed for the parallel functional analysis of different genetic variants
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