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$^2$). 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 $\Lambda$CDM model. Duplicate entries were carefully handled. I produced three catalogs: LC$^2$-single, with 485 unique groups and clusters analysed with the single-halo model; LC$^2$-substructure, listing substructures in complex systems; LC$^2$-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, $\sigma_\mathrm{WL}\sim$15 per cent for WL masses and $\sigma_\mathrm{HE}\sim$25 per cent for HE masses. The certain assessment of the bias is hampered by differences as large as $\sim$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 $\Omega_\Lambda = 1.1$ with a statistical error of $\pm 0.2$. Including the constraint of a flat universe and an equation of state for the dark energy $w_X \geq -1$, we obtain $\Omega_M = 0.10 \pm 0.10$ and $w_X = -0.84 \pm 0.14$. Relaxing the prior on $w_X$, we find that the null energy condition is satisfied at the 3-$\sigma$ 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 $Y_{500}$-$M_{500}$ 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 $20\pm10$ per cent. The absolute calibration of the relation can not be ascertained due to systematic differences of $\sim$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, $\sim$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