ALBERT

Description: We present a series of new, publicly available mock catalogs of X-ray selected active galactic nuclei (AGNs), nonactive galaxies, and clusters of galaxies. These mocks are based on up-to-date observational results on the demographic of extragalactic X-ray sources and their extrapolations. They reach fluxes below 10−20 erg cm−2 s−1 in the 0.5–2 keV band, that is, more than an order of magnitude below the predicted limits of future deep fields, and they therefore represent an important tool for simulating extragalactic X-ray surveys with both current and future telescopes. We used our mocks to perform a set of end-to-end simulations of X-ray surveys with the forthcoming ATHENA mission and with the AXIS probe, a subarcsecond resolution X-ray mission concept proposed to the Astro 2020 Decadal Survey. We find that these proposed, next generation surveys may transform our knowledge of the deep X-ray Universe. As an example, in a total observing time of 15 Ms, AXIS would detect ∼225 000 AGNs and ∼50 000 nonactive galaxies, reaching a flux limit of f0.5−2 ∼ 5 × 10−19 erg cm−2 s−1 in the 0.5–2 keV band, with an improvement of over an order of magnitude with respect to surveys with current X-ray facilities. Consequently, 90% of these sources would be detected for the first time in the X-rays. Furthermore, we show that deep and wide X-ray surveys with instruments such as AXIS and ATHENA are expected to detect ∼20 000 z 〉 3 AGNs and ∼250 sources at redshift z 〉 6, thus opening a new window of knowledge on the evolution of AGNs over cosmic time and putting strong constraints on the predictions of theoretical models of black hole seed accretion in the early universe.

Description: The application to observational data of the generalized scaling relations (gSRs) presented in Ettori et al. 2012 is here discussed. We extend further the formalism of the gSR in the self-similar model for X-ray galaxy clusters, showing that for a generic relation $M_{\rm tot} \propto L^{\alpha } M_{\rm g}^{\beta } T^{\gamma }$ , where L , M g and T are the gas luminosity, mass and temperature, respectively, the values of the slopes lay in the plane 4α + 3β + 2 = 3. Using published data set, we show that some projections of the gSR are the most efficient relations, holding among observed physical quantities in the X-ray band, to recover the cluster gravitating mass. This conclusion is based on the evidence that they provide the lowest 2 , the lowest total scatter and the lowest intrinsic scatter among the studied scaling laws on both galaxy group and cluster mass scales. By the application of the gSR, the intrinsic scatter is reduced in all the cases down to a relative error on the reconstructed mass below 16 per cent. The best-fitting relations are $M_{\rm tot} \propto M_{\rm g}^a T^{1.5-1.5 a}$ , with a 0.4, and M tot    L a T 1.5 – 2 a , with a 0.15. As by-product of this study, we provide the estimates of the gravitating mass at  = 500 for 120 objects (50 from the Mahdavi et al. sample, 16 from Maughan sample; 31 from Pratt et al. sample; 23 from Sun et al. sample), 114 of which are unique entries. The typical relative error on the mass provided from the gSR only (i.e. not propagating any uncertainty associated with the observed quantities) ranges between 3 and 5 per cent on cluster scale and is about 10 per cent for galaxy groups. With respect to the hydrostatic values used to calibrate the gSR, the masses are recovered with deviations of the order of 10 per cent due to the different mix of relaxed/disturbed objects present in the considered samples. In the extreme case of a gSR calibrated with relaxed systems, the hydrostatic mass in disturbed objects is overestimated by about 20 per cent.

Description: The relation between mass and concentration of galaxy clusters traces their formation and evolution. Massive lensing clusters were observed to be overconcentrated and following a steep scaling in tension with predictions from the concordance cold dark matter (CDM) paradigm. We critically revise the relation in the CLASH (Cluster Lensing And Supernova survey with Hubble), the SGAS (Sloan Giant Arcs Survey), the LOCUSS (Local Cluster Substructure Survey), and the high-redshift samples of weak lensing clusters. Measurements of mass and concentration are anti-correlated, which can bias the observed relation towards steeper values. We corrected for this bias and compared the measured relation to theoretical predictions accounting for halo triaxiality, adiabatic contraction of the halo, presence of a dominant brightest cluster galaxy, and, mostly, selection effects in the observed sample. The normalization, the slope, and the scatter of the expected relation are strongly sample-dependent. For the considered samples, the predicted slope is much steeper than that of the underlying relation characterizing dark matter-only clusters. We found that the correction for statistical and selection biases in observed relations mostly solve the tension with the CDM model.

Description: 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, WL  ~ 15 per cent for WL masses and HE  ~ 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 overestimated.

Description: We discuss the scaling relation between mass and integrated Compton parameter of a sample of galaxy clusters from the all-sky 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 ± 10 per cent. The absolute calibration of the relation cannot 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.

Description: The scaling of observable properties of galaxy clusters with mass evolves with time. Assessing the role of the evolution is crucial to study the formation and evolution of massive haloes and to avoid biases in the calibration. We present a general method to infer the mass and the redshift dependence, and the time-evolving intrinsic scatter of the mass–observable relations. The procedure self-calibrates the redshift-dependent completeness function of the sample. The intrinsic scatter in the mass estimates used to calibrate the relation is considered too. We apply the method to the scaling of mass $M_\Delta$ versus line-of-sight galaxy velocity dispersion v , optical richness, X-ray luminosity, L X , and Sunyaev–Zel'dovich signal. Masses were calibrated with weak lensing measurements. The measured relations are in good agreement with time and mass dependences predicted in the self-similar scenario of structure formation. The lone exception is the $L_\mathrm{X} {\rm -} M_\Delta$ relation, whose time evolution is negative in agreement with formation scenarios with additional radiative cooling and uniform preheating at high redshift. The intrinsic scatter in the $\sigma _\mathrm{v} {\rm -} M_\Delta$ relation is notably small, of the order of 14 per cent. Robust predictions on the observed properties of the galaxy clusters in the Cluster Lensing And Supernova survey with Hubble sample are provided as cases of study. Catalogues and scripts are publicly available at http://pico.bo.astro.it/{small tilde}sereno/CoMaLit/ .

Description: In galaxy clusters, the relations between observables in X-ray and millimetre 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 β 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 three physical quantities, and measure C 0.5 f g  = 0.110( ± 0.002 ± 0.002)( E z M /5 10 14 M ) 0.198( ± 0.025 ± 0.04) and β P  = –dln P /dln r  = 3.14( ± 0.04 ± 0.02)( E z M /5 10 14 M ) 0.071( ± 0.012 ± 0.004) , where both a statistical and systematic error (the latter mainly due to the cross-calibration uncertainties affecting the Chandra and XMM–Newton 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 β P define an intercorrelated internally consistent set of scaling relations that reproduces the mass estimates with the lowest residuals.

Description: The reconstruction of galaxy cluster's gas density profiles is usually performed by assuming spherical symmetry and averaging the observed X-ray emission in circular annuli. In the case of a very inhomogeneous and asymmetric gas distribution, this method has been shown to return biased results in numerical simulations because of the n 2 dependence of the X-ray emissivity. We propose a method to recover the true density profiles in the presence of inhomogeneities, based on the derivation of the azimuthal median of the surface brightness in concentric annuli. We demonstrate the performance of this method with numerical simulations, and apply it to a sample of 31 galaxy clusters in the redshift range 0.04–0.2 observed with ROSAT /Position Sensitive Proportional Counter (PSPC). The clumping factors recovered by comparing the mean and the median are mild and show a slight trend of increasing bias with radius. For R  〈  R 500 , we measure a clumping factor $\sqrt{C} 〈 1.1$ , which indicates that the thermodynamic properties and hydrostatic masses measured in this radial range are only mildly affected by this effect. Comparing our results with three sets of hydrodynamical numerical simulations, we found that non-radiative simulations significantly overestimate the level of inhomogeneities in the intracluster medium, while the runs including cooling, star formation, and AGN feedback reproduce the observed trends closely. Our results indicate that most of the accretion of X-ray-emitting gas is taking place in the diffuse, large-scale accretion patterns rather than in compact structures.

Description: We study how well halo properties of galaxy clusters, such as mass and concentration, are recovered using lensing data. In order to generate a large sample of systems at different redshifts, we use the code moka . We measure halo mass and concentration using weak lensing data alone (WL), fitting to a Navarro, Frenk & White (NFW) profile the reduced tangential shear profile, or by combining weak and strong lensing data, by adding information about the size of the Einstein radius (WL+SL). For different redshifts, we measure the mass and the concentration biases and find that these are mainly caused by the random orientation of the halo ellipsoid with respect to the line of sight. Since our simulations account for the presence of a bright central galaxy, we perform mass and concentration measurements using a generalized NFW profile which allows for a free inner slope. This reduces both the mass and the concentration biases. We discuss how the mass function and the concentration–mass relation change when using WL and WL+SL estimates. We investigate how selection effects impact the measured concentration–mass relation showing that strong lens clusters may have a concentration 20–30 per cent higher than the average, at fixed mass, considering also the particular case of strong lensing selected samples of relaxed clusters. Finally, we notice that selecting a sample of relaxed galaxy clusters, as is done in some cluster surveys, explains the concentration–mass relation biases.

Description: In this work, we present an analytic framework for calculating the individual and joint distributions of the n th most massive or n th highest redshift galaxy cluster for a given survey characteristic allowing us to formulate cold dark matter (CDM) exclusion criteria. We show that the cumulative distribution functions steepen with increasing order, giving them a higher constraining power with respect to the extreme value statistics. Additionally, we find that the order statistics in mass (being dominated by clusters at lower redshifts) is sensitive to the matter density and the normalization of the matter fluctuations, whereas the order statistics in redshift is particularly sensitive to the geometric evolution of the Universe. For a fixed cosmology, both order statistics are efficient probes of the functional shape of the mass function at the high-mass end. To allow a quick assessment of both order statistics, we provide fits as a function of the survey area that allow percentile estimation with an accuracy better than 2 per cent. Furthermore, we discuss the joint distributions in the two-dimensional case and find that for the combination of the largest and the second largest observation, it is most likely to find them to be realized with similar values with a broadly peaked distribution. When combining the largest observation with higher orders, it is more likely to find a larger gap between the observations and when combining higher orders in general, the joint probability density function peaks more strongly. Having introduced the theory, we apply the order statistical analysis to the Southpole Telescope (SPT) massive cluster sample and metacatalogue of X-ray detected clusters of galaxies catalogue and find that the 10 most massive clusters in the sample are consistent with CDM and the Tinker mass function. For the order statistics in redshift, we find a discrepancy between the data and the theoretical distributions, which could in principle indicate a deviation from the standard cosmology. However, we attribute this deviation to the uncertainty in the modelling of the SPT survey selection function. In turn, by assuming the CDM reference cosmology, order statistics can also be utilized for consistency checks of the completeness of the observed sample and of the modelling of the survey selection function.