150 research outputs found
CoMaLit III. Literature Catalogs of weak Lensing Clusters of galaxies (LC^2)
The measurement of the mass of clusters of galaxies is crucial for their use
in cosmology and astrophysics. Masses can be efficiently determined with weak
lensing (WL) analyses. I compiled Literature Catalogs of weak Lensing Clusters
(LC). Cluster identifiers, coordinates, and redshifts have been
standardised. WL masses were reported to over-densities of 2500, 500, 200, and
to the virial one in the reference CDM model. Duplicate entries were
carefully handled. I produced three catalogs: LC-single, with 485 unique
groups and clusters analysed with the single-halo model; LC-substructure,
listing substructures in complex systems; LC-all, listing all the 822 WL
masses found in literature. The catalogs and future updates are publicly
available at http://pico.bo.astro.it/~sereno/CoMaLit/LC2/.Comment: 10 pages, 4 figures. v2: MNRAS in press; minor changes; updated link.
The catalogs and future updates will be hosted at
http://pico.bo.astro.it/~sereno/CoMaLit/LC2
The mass-concentration relation in massive galaxy clusters at redshift ~1
Mass and concentration of clusters of galaxies are related and evolving with
redshift. We study the properties of a sample of 31 massive galaxy clusters at
high redshift, 0.8 < z < 1.5, using weak and strong lensing observations.
Concentration is a steep function of mass, c_{200} ~M_{200}^{-0.83 +-0.39},
with higher-redshift clusters being less concentrated. Mass and concentration
from the stacked analysis, M_{200}=(4.1+-0.4)x10^{14}M_Sun/h and
c_{200}=2.3+-0.2, are in line with theoretical results extrapolated from the
local universe. Clusters with signs of dynamical activity preferentially
feature high concentrations. We discuss the possibility that the whole sample
is a mix of two different kinds of haloes. Over-concentrated clusters might be
accreting haloes out of equilibrium in a transient phase of compression,
whereas less concentrated ones might be more relaxed.Comment: 10 pages, 3 figures; in press on MNRA
Hubble constant and dark energy inferred from free-form determined time delay distances
Time delays between multiple images of lensed sources can probe the geometry
of the universe. We propose a novel method based on free-form modelling of
gravitational lenses to estimate time-delay distances and, in turn,
cosmological parameters. This approach does not suffer from the degeneracy
between the steepness of the profile and the cosmological parameters. We apply
the method to 18 systems having time delay measurements and find
H_0=69+-6(stat.)+-4(syst.) km s^{-1}Mpc^{-1}. In combination with WMAP9, the
constraints on dark energy are Omega_w=0.68+-0.05 and w=-0.86+-0.17 in a flat
model with constant equation-of-state.Comment: 6 pages; accepted for publication on MNRA
Comparing Masses in Literature (CoMaLit)-I. Bias and scatter in weak lensing and X-ray mass estimates of clusters
The first building block to use galaxy clusters in astrophysics and cosmology
is the accurate determination of their mass. Two of the most well regarded
direct mass estimators are based on weak lensing (WL) determinations or X-ray
analyses assuming hydrostatic equilibrium (HE). By comparing these two mass
measurements in samples of rich clusters, we determined the intrinsic scatters,
15 per cent for WL masses and
25 per cent for HE masses. The certain assessment of
the bias is hampered by differences as large as 40 per cent in either WL
or HE mass estimates reported by different groups. If the intrinsic scatter in
the mass estimate is not considered, the slope of any scaling relation
`observable--mass' is biased towards shallower values, whereas the intrinsic
scatter of the scaling is over-estimated.Comment: 14 pages, 7 figures; v2: 16 pages, 8 figures, MNRAS in press; results
unchanged; extended presentation of the statistical method and of the
correlations; products from the CoMaLit series are hosted and updated at
http://pico.bo.astro.it/~sereno/CoMaLi
Determining cosmological parameters from X-ray measurements of strong lensing clusters
We discuss a new method which is potentially capable of constraining cosmological parameters using observations of giant luminous arcs in rich X-ray clusters of galaxies. The mass profile and the mass normalization of the lenses are determined from X-ray measurements. The method also allows to probe the amount and equation of state of the dark energy in the universe. The analysis of a preliminary sample of 6 luminous, relatively relaxed clusters of galaxies strongly favours an accelerating expansion of the universe. Under the assumption that the dark energy is in the form of a cosmological constant, the data provide an estimate of with a statistical error of . Including the constraint of a flat universe and an equation of state for the dark energy , we obtain and . Relaxing the prior on , we find that the null energy condition is satisfied at the 3- confidence level
Comparison of weak lensing by NFW and Einasto halos and systematic errors
Recent N-body simulations have shown that Einasto radial profiles provide the
most accurate description of dark matter halos. Predictions based on the
traditional NFW functional form may fail to describe the structural properties
of cosmic objects at the percent level required by precision cosmology. We
computed the systematic errors expected for weak lensing analyses of clusters
of galaxies if one wrongly models the lens density profile. Even though the NFW
fits of observed tangential shear profiles can be excellent, viral masses and
concentrations of very massive halos (>~ 10^{15}M_Sun/h) can be over- and
underestimated by ~10 per cent, respectively. Misfitting effects also steepen
the observed mass-concentration relation, as observed in multi-wavelength
observations of galaxy groups and clusters. Based on shear analyses, Einasto
and NFW halos can be set apart either with deep observations of exceptionally
massive structures (>~ 2\times10^{15}M_Sun/h) or by stacking the shear profiles
of thousands of group-sized lenses (>~ 10^{14}M_Sun/h).Comment: 12 pages, 4 figures, in press on JCAP; v02: cosmic noise include
Parameter estimation for coalescing massive binary black holes with LISA using the full 2-post-Newtonian gravitational waveform and spin-orbit precession
With one exception, previous analyses of the measurement accuracy of
gravitational wave experiments for comparable-mass binary systems have
neglected either spin-precession effects or subdominant harmonics and amplitude
modulations. Here we give the first explicit description of how these effects
combine to improve parameter estimation. We consider supermassive black hole
binaries as expected to be observed with the planned space-based interferometer
LISA, and study the measurement accuracy for several astrophysically
interesting parameters obtainable taking into account the full 2PN waveform for
spinning bodies, as well as spin-precession effects. We find that for binaries
with a total mass in the range 10^5 M_Sun < M < 10^7 M_Sun at a redshift of 1,
a factor ~1.5 is in general gained in accuracy, with the notable exception of
the determination of the individual masses in equal-mass systems, for which a
factor ~5 can be gained. We also find, as could be expected, that using the
full waveform helps increasing the upper mass limit for detection, which can be
as high as M = 10^8 M_Sun at a redshift of 1, as well as the redshift limit
where some information can be extracted from a system, which is roughly z = 10
for M < 10^7 M_Sun, 1.5-5 times higher than with the restricted waveform. We
computed that the full waveform allows to use supermassive black hole binaries
as standard sirens up to a redshift of z = 1.6, about 0.4 larger than what
previous studies allowed. We found that for lower unequal-mass binary systems,
the measurement accuracy is not as drastically improved as for other systems.
This suggests that for these systems, adding parameters such as eccentricity or
alternative gravity parameters could be achieved without much loss in the
accuracy.Comment: 20 pages, 20 figure
CoMaLit - II. The scaling relation between mass and Sunyaev-Zel'dovich signal for Planck selected galaxy clusters
We discuss the scaling relation between mass and integrated Compton parameter
of a sample of galaxy clusters from the all-sky {\it Planck} Sunyaev-Zel'dovich
catalogue. Masses were measured with either weak lensing, caustics techniques,
or assuming hydrostatic equilibrium. The retrieved - relation
does not strongly depend on the calibration sample. We found a slope of
1.4-1.9, in agreement with self-similar predictions, with an intrinsic scatter
of per cent. The absolute calibration of the relation can not be
ascertained due to systematic differences of 20-40 per cent in mass
estimates reported by distinct groups. Due to the scatter, the slope of the
conditional scaling relation, to be used in cosmological studies of number
counts, is shallower, 1.1-1.6. The regression methods employed account
for intrinsic scatter in the mass measurements too. We found that Planck mass
estimates suffer from a mass dependent bias.Comment: 14 pages, 7 figures; v2: 17 pages, 11 figures; MNRAS in press,
results unchanged; extended discussion of the Planck calibration sample;
added discussion of conditional vs symmetric scaling relations and of mixture
of Gaussian functions as distribution of the independent variable; products
from the CoMaLit series at http://pico.bo.astro.it/~sereno/CoMaLi
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