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• Paper pool
  • Weighted ABC: a new strategy for cluster strong lensing cosmology with simulations
  • The universality of the virial halo mass function and models for non-universality of other halo definitions
  • Evolution of the luminosity-to-halo mass relation of LRGs from a combined SDSS-DR10+RCS2 analysis
  • Mass Calibration of Galaxy Clusters at Redshift 0.1-1.0 using Weak Lensing in the Sloan Digital Sky Survey Stripe 82 Co-add
  • The physics inside the scaling relations for X-ray galaxy clusters: gas clumpiness, gas mass fraction and slope of the pressure profile
  • A Simple Physical Model for the Gas Distribution in Galaxy Clusters
  • Brightest X-ray clusters of galaxies in the CFHTLS wide fields: Catalog and optical mass estimator
  • Deconstructing Thermal Sunyaev-Zel'dovich - Gravitational Lensing Cross-Correlations: Implications for the Intracluster Medium
  • Dissecting the thermal Sunyaev-Zeldovich-gravitational lensing cross-correlation with hydrodynamical simulations

Weighted ABC: a new strategy for cluster strong lensing cosmology with simulations¶

Madhura Killedar, Stefano Borgani, Dunja Fabjan, Klaus Dolag, Gian Luigi Granato, Massimo Meneghetti, Susana Planelles, Cinthia Ragone-Figueroa

Comparisons between observed and predicted strong lensing properties of galaxy clusters have been routinely used to claim either tension or consistency with ΛCDM cosmology. However, standard approaches to such cosmological tests are unable to quantify the preference for one cosmology over another. We advocate using a `weighted' variant of approximate Bayesian computation (ABC), whereby the parameters of the scaling relation between Einstein radii and cluster mass, α and β, are treated as summary statistics. We demonstrate, for the first time, a method of estimating the likelihood of the data under the ΛCDM framework, using the X-ray selected z>0.5 MACS clusters as a case in point and employing both N-body and hydrodynamic simulations of clusters. We investigate the uncertainty in the calculated likelihood, and consequential ability to compare competing cosmologies, that arises from incomplete descriptions of baryonic processes, discrepancies in cluster selection criteria, redshift distribution, and dynamical state. The relation between triaxial cluster masses at various overdensities provide a promising alternative to the strong lensing test.

The universality of the virial halo mass function and models for non-universality of other halo definitions¶

Giulia Despali, Carlo Giocoli, Raul E. Angulo, Giuseppe Tormen, Ravi K. Sheth, Giacomo Baso, Lauro Moscardini

The abundance of galaxy clusters can constrain both the geometry and structure growth in our Universe. However, this probe could be significantly complicated by recent claims of nonuniversality -- non-trivial dependences with respect to the cosmological model and redshift. In this work we analyse the dependance of the mass function on the way haloes are identified and establish if this can cause departures from universality. In order to explore this dependance, we use a set of different dark matter only cosmological simulations (Le SBARBINE simulations), with the latest cosmological parameters from the Planck collaboration; this first suite of simulations is followed by a lower resolution set carry out with different cosmological parameters. We identify dark matter haloes using a Spherical Overdensity algorithm with varying overdensity thresholds (virial, 2000ρc, 1000ρc, 500ρc, 200ρc and 200ρb) at all redshifts. We notice that, when expressed in term of the rescaled variable ν, the mass function for virial haloes can be considered universal as a function of redshift and cosmology, while this is clearly not the case for the other considered overdensities. We provide fitting functions for the halo mass function parameters as a function of density, that allow to predict, with a few percent accuracy, the halo mass function for a wide range of halo definitions, redshifts and cosmological models. We then present how the departures from universality associated with other halo definitions can be derived by combining the universality of the virial definition with the expected shape of the density profile of halos.

Evolution of the luminosity-to-halo mass relation of LRGs from a combined SDSS-DR10+RCS2 analysis¶

Edo van Uitert, Marcello Cacciato, Henk Hoekstra, Ricardo Herbonnet

We study the evolution of the luminosity-to-halo mass relation of Luminous Red Galaxies (LRGs). We select a sample of 52 000 LOWZ and CMASS LRGs from the Baryon Oscillation Spectroscopic Survey (BOSS) SDSS-DR10 in the ~450 deg^2 that overlaps with imaging data from the second Red-sequence Cluster Survey (RCS2), group them into bins of absolute magnitude and redshift and measure their weak lensing signals. The source redshift distribution has a median of 0.7, which allows us to study the lensing signal as a function of lens redshift. We interpret the lensing signal using a halo model, from which we obtain the halo masses as well as the normalisations of the mass-concentration relations. We find that the concentration of haloes that host LRGs is consistent with dark matter only simulations once we allow for miscentering or satellites in the modelling. The slope of the luminosity-to-halo mass relation has a typical value of 1.4 and does not change with redshift, but we do find evidence for a change in amplitude: the average halo mass of LOWZ galaxies increases by 25_{-14}^{+16} % between z=0.36 and 0.22 to an average value of 6.43+/-0.52 x 10^13 h70^-1 Msun. If we extend the redshift range using the CMASS galaxies and assume that they are the progenitors of the LOWZ sample, we find that the average mass of LRGs increases by 80^{+39}_{-28} % between z=0.6 and 0.2

Mass Calibration of Galaxy Clusters at Redshift 0.1-1.0 using Weak Lensing in the Sloan Digital Sky Survey Stripe 82 Co-add¶

Matthew P. Wiesner, Huan Lin, Marcelle Soares-Santos

We present mass-richness relations found in the Sloan Digital Sky Survey Stripe 82 co-add. These relations were found using stacked weak lensing shear observed in a large sample of galaxy clusters. These mass-richness relations are presented for four redshift bins, 0.1<z≤0.4, 0.4<z≤0.7, 0.7<z≤1.0 and 0.1<z≤1.0. We describe the sample of galaxy clusters and explain how these clusters were found using a Voronoi Tessellation cluster finder. We fit an NFW profile to the stacked weak lensing shear signal in redshift and richness bins in order to measure virial mass (M200). We describe several effects that can bias weak lensing measurements, including photometric redshift bias, the effect of the central BCG, halo miscentering, photometric redshift uncertainty and foreground galaxy contamination. We present mass-richness relations using richness measure NVT with each of these effects considered separately as well as considered altogether. We present values for the mass coefficient (M200|20) and the power law slope (α) for power law fits to the mass and richness values in each of the redshift bins. We find values of the mass coefficient of 8.30±0.682, 13.8±1.94, 27.3±14.7 and 8.61±0.719×1013h−1Msun for each of the four redshift bins respectively. We find values of the power law slope of 0.988±0.0716, 0.962±0.130, 1.52±0.483 and 1.01±0.0803 respectively. Finally, we examine redshift evolution of the mass-richness relation.

The physics inside the scaling relations for X-ray galaxy clusters: gas clumpiness, gas mass fraction and slope of the pressure profile¶

S. Ettori (INAF-OA Bologna)

In galaxy clusters, the relations between observables in X-ray and millimeter wave bands and the total mass have normalizations, slopes and redshift evolutions that are simple to estimate in a self-similar scenario. We study these scaling relations and show that they can be efficiently expressed, in a more coherent picture, by fixing the normalizations and slopes to the self-similar predictions, and advocating, as responsible of the observed deviations, only three physical mass-dependent quantities: the gas clumpiness $C$, the gas mass fraction $f_g$ and the logarithmic slope of the thermal pressure profile $\beta_P$. We use samples of the observed gas masses, temperature, luminosities, and Compton parameters in local clusters to constrain normalization and mass dependence of these 3 physical quantities, and measure: $C^{0.5} f_g = 0.110 (\pm 0.002 \pm 0.002) \left( E_z M / 5 \times 10^{14} M_{\odot} \right)^{0.198 (\pm 0.025 \pm 0.04)}$ and $\beta_P = -d \ln P/d \ln r = 3.14 (\pm 0.04 \pm 0.02) \left( E_z M / 5 \times 10^{14} M_{\odot} \right)^{0.071 (\pm 0.012 \pm 0.004)}$, where both a statistical and systematic error (the latter mainly due to the cross-calibration uncertainties affecting the \cxo\ and \xmm\ results used in the present analysis) are quoted. The degeneracy between $C$ and $f_g$ is broken by using the estimates of the Compton parameters. Together with the self-similar predictions, these estimates on $C$, $f_g$ and $\beta_P$ define an inter-correlated internally-consistent set of scaling relations that reproduces the mass estimates with the lowest residuals.

A Simple Physical Model for the Gas Distribution in Galaxy Clusters¶

Anna Patej, Abraham Loeb

The dominant baryonic component of galaxy clusters is hot gas whose distribution is commonly probed through X-ray emission arising from thermal bremsstrahlung. The density profile thus obtained has been traditionally modeled with a beta-profile, a simple function with only three parameters. However, this model is known to be insufficient for characterizing the range of cluster gas distributions, and attempts to rectify this shortcoming typically introduce additional parameters to increase the fitting flexibility. We use cosmological and physical considerations to obtain a family of profiles for the gas with fewer parameters than the beta-model but which better accounts for observed gas profiles over wide radial intervals.

Brightest X-ray clusters of galaxies in the CFHTLS wide fields: Catalog and optical mass estimator¶

M. Mirkazemi, A. Finoguenov, M. J. Pereira, M. Tanaka, M. Lerchster, F. Brimioulle, E. Egami, K. Kettula, G. Erfanianfar, H. J. McCracken, Y. Mellier, J. P. Kneib, E. Rykoff, S. Seitz, T. Erben, J. E. Taylor

The CFHTLS presents a unique data set for weak lensing studies, having high quality imaging and deep multi-band photometry. We have initiated an XMM-CFHTLS project to provide X-ray observations of the brightest X-ray selected clusters within the wide CFHTLS area. Performance of these observations and the high quality of CFHTLS data, allows us to revisit the identification of X-ray sources, introducing automated reproducible algorithms, based on the multi-color red sequence finder. We have also introduced a new optical mass proxy. We provide the calibration of the red sequence observed in the CFHT filters and compare the results with the traditional single color red sequence and photoz. We test the identification algorithm on the subset of highly significant XMM clusters and identify 100% of the sample. We find that the integrated z-band luminosity of the red sequence galaxies correlates well with the X-ray luminosity with a surprisingly small scatter of 0.20 dex. We further use the multi-color red sequence to reduce spurious detections in the full XMM and RASS data sets, resulting in catalogs of 196 and 32 clusters, respectively. We made spectroscopic follow-up observations of some of these systems with HECTOSPEC and in combination with BOSS DR9 data. We also describe the modifications needed to the source detection algorithm in order to keep high purity of extended sources in the shallow X-ray data. We also present the scaling relation between X-ray luminosity and velocity dispersion.

Deconstructing Thermal Sunyaev-Zel'dovich - Gravitational Lensing Cross-Correlations: Implications for the Intracluster Medium¶

N. Battaglia (Princeton), J. C. Hill (Columbia), N. Murray (CITA)

Recent first detections of the cross-correlation of the thermal Sunyaev-Zel'dovich (tSZ) signal in Planck cosmic microwave background (CMB) temperature maps with gravitational lensing maps inferred from the Planck CMB data and the CFHTLenS galaxy survey provide new probes of the relationship between baryons and dark matter. Using cosmological hydrodynamics simulations, we show that these cross-correlation signals are dominated by contributions from hot gas in the intracluster medium (ICM), rather than diffuse, unbound gas located beyond the virial radius (the "missing baryons"). Thus, these cross-correlations offer a tool with which to study the ICM over a wide range of halo masses and redshifts. In particular, we show that the tSZ - CMB lensing cross-correlation is more sensitive to gas in lower-mass, higher-redshift halos and gas at larger cluster-centric radii than the tSZ - galaxy lensing cross-correlation. Combining these measurements with primary CMB data will constrain feedback models through their signatures in the ICM pressure profile. We forecast the ability of ongoing and future experiments to constrain such ICM parameters, including the mean amplitude of the pressure - mass relation, the redshift evolution of this amplitude, and the mean outer logarithmic slope of the pressure profile. The results are promising, with ≈5−20% precision constraints achievable with upcoming experiments, even after marginalizing over cosmological parameters.

Dissecting the thermal Sunyaev-Zeldovich-gravitational lensing cross-correlation with hydrodynamical simulations¶

Alireza Hojjati, Ian G. McCarthy, Joachim Harnois-Deraps, Yin-Zhe Ma, Ludovic Van Waerbeke, Gary Hinshaw, Amandine M. C. Le Brun

We use the cosmo-OWLS suite of cosmological hydrodynamical simulations, which includes different galactic feedback models, to predict the cross-correlation signal between weak gravitational lensing and the thermal Sunyaev-Zeldovich (tSZ) y-parameter. The predictions are compared to the recent detection reported by van Waerbeke and collaborators. The simulations reproduce the weak lensing-tSZ cross-correlation, ξyκ(θ), well. The uncertainty arising from different possible feedback models appears to be important on small scales only (θ≲10 arcmin), while the amplitude of the correlation on all scales is sensitive to cosmological parameters that control the growth rate of structure (such as σ8, Ωm and Ωb). This study confirms our previous claim (in Ma et al.) that a significant proportion of the signal originates from the diffuse gas component in low-mass (Mhalo≲1014M⊙) clusters as well as from the region beyond the virial radius. We estimate that approximately 20% of the detected signal comes from low-mass clusters, which corresponds to about 30% of the baryon density of the Universe. The simulations also suggest that more than half of the baryons in the Universe are in the form of diffuse gas outside halos (≳5 times the virial radius) which is not hot or dense enough to produce a significant tSZ signal or be observed by X-ray experiments. Finally, we show that future high-resolution tSZ-lensing cross-correlation observations will serve as a powerful tool for discriminating between different galactic feedback models.