Optical characterisation of the planck psz1 galaxy cluster catalogue building a reference sample for cosmology

This thesis has been dedicated to the study of Galaxy Clusters as Cosmological tools. The work is divided into two main parts; the first is purely observational, whereas the second is dedicated to the preparation of tools for cosmological analyses. The observational section has been developed within the frame of the optical validation program Sunyaev-Zeldovich (SZ) sources, observed by the Planck satellite in the northern hemisphere, and included in the PSZ1 catalogue. The 212 targets were observed during a two-year International Time Project (ITP) at the Roque de Los Muchachos Observatory (ORM) facilities on La Palma Island. During the observational programme, each target underwent a validation process in two phases: photometric and spectroscopic. In the first phase, we performed imaging in g0, r 0 and i0-bands at INT/WFC and WHT/ACAM. We obtained a deep photometry for the majority of the targets, reaching a magnitude in r 0-band of about 23.2 and 23.8 for WFC/INT and ACAM/WHT, respectively. This allowed us to estimate their photometric redshift up to zphot 0:8 cluster richness. In the second phase, we performed the spectroscopy of the photometrically-confirmed clusters. We used TNG/DOLORES and GTC/OSIRIS spectrographs in order to observe clusters at zphot 0:4 and zphot > 0:4, respectively. The aim of the spectroscopic follow-up is to confirm clusters and to characterise their physical properties, such as velocity dispersion and mass. We used the Multi-Object Spectroscopy (MOS) technique in order to observe as many cluster members as possible. Due to the large sample of SZ effect sources, we were able to use, on average, only one mask per cluster, so we retrieved a median number of cluster members of Ngal 14. Due to this low number of galaxy members we could not use sophisticated membership techniques. Therefore, we assigned the cluster membership according to the galaxy radial velocity and distance from the cluster centre. At the end of the follow-up programme we were able to validate for the first time a total of 88 new galaxy clusters. The second part of this thesis is focused in the cosmology, with the main aim of estimating the mass bias parameter (1b) through the characterisation of the scaling relation between the cluster masses calculated from dynamical and SZ proxies. The Planck Collaboration demonstrated that the mass bias is crucial to determine the cosmological parameters m and 8 by using the cluster number counts formalism. The Planck Collaboration showed that the latter are in tension with the parameters derived from CMB primary anisotropies, and that, by varying the mass bias parameter, this tension could be alleviated. Since the (1b) should be a measure of the bias of the SZ mass estimation, it is extremely important to understand the possible biases in the dynamical mass estimate. It is impossible to obtain an accurate dynamical mass estimate if the velocity dispersion is biased. The nature of the biases may be statistical or physical, and in this thesis we studied both kinds of biases by using hydrodynamic simulations. We tested three velocity dispersion estimators, namely biweight, gapper and standard deviation, and observed that they present a statistical bias in the low galaxy numbers regime. In order to correct this effect, we designed a receipt to obtain unbiased velocity dispersions in the whole Ngal regime. Physical biases are mainly related to the cluster members sampling. For instance, due to the velocity dispersion radial profile a 5% bias is introduced when clusters are sampled in their cores only. We also observed that the velocity dispersion estimate obtained by using only the most massive galaxy members is biased by about 2%. However, the most important source of bias is the interlopers contamination, which overestimates the velocity dispersion by about 10%. Furthermore, we demonstrated that even an unbiased velocity dispersion could lead to a biased estimate of the cluster mass. We defined new mass estimator, which takes into account this statistical effect. In order to perform the cosmological analysis, we selected all clusters within the ITP sample with reliable velocity dispersion estimation (more than 7 members and no multiple detections). On the other hand, in order to improve the statistical significance of our study, we applied the cluster identification procedure to the PSZ1 clusters within the SDSS footprint as well. This way, we built a sample of 207 galaxy clusters. This sample is the largest catalogue of clusters for which both the SZ and dynamic masses have been estimated. Based on it and after applying all corrections, we found that the mass bias parameters is (1 B) = 0:78 0:02. The compatibility of this result with the one obtained by the Planck Collaboration ensures that we are not able to alleviate the tension on the cosmological parameters. However, we were able to reduce the uncertainty on the mass bias down to 2% for the first time, based on velocity dispersion mass estimators. Therefore, although the parameter estimates will not vary, our result will allow us to reduce the uncertainty on the combination of m and 8 by about a factor 2 with respect to previous studies. Other solutions are discussed

Galaxy clusters morphology with Zernike polynomials: the first application on Planck\textit{Planck} Compton parameter maps

International audienceThe study of the morphology of 2D projected maps of galaxy clusters is a suitable approach to infer, from real data, the dynamical state of those systems. We recently developed a new method to recover the morphological features in galaxy cluster maps which consists of an analytical modelling through the Zernike polynomials. After the first validation of this approach on a set of high-resolution mock maps of the Compton parameter, $y$, from hydrodynamically simulated galaxy clusters in THE THREE HUNDRED project, we apply the Zernike modelling on $y$-maps of local ($z < 0.1$) galaxy clusters observed by the $Planck$ satellite. With a single parameter collecting the main information of the Zernike modelling, we classify their morphology. A set of mock $Planck$-like $y$-maps, generated from THE THREE HUNDRED clusters, is also used to validate our indicator with a proper dynamical state classification. This approach allows us to test the efficiency of the Zernike morphological modelling in evaluating the dynamical population in the real $Planck$ sample

Gravitational lensing detection of an extremely dense environment around a galaxy cluster

Galaxy clusters form at the highest-density nodes of the cosmic web. The clustering of dark matter halos hosting these galaxy clusters is enhanced relative to the general mass distribution, with the matter density beyond the virial region being strongly correlated to the halo mass (halo bias). Halo properties other than mass can further enhance the halo clustering (secondary bias). Observational campaigns have ascertained the halo bias, but efforts to detect this secondary bias for massive halos have been inconclusive. Here, we report the analysis of the environment bias in a sample of massive clusters, selected through the Sunyaev–Zel’dovich effect by the Planck mission, focusing on the detection of the environment dark matter correlated to a single cluster, PSZ2 G099.86+58.45. The gravitational lensing signal of the outskirts is very large and can be traced up to 30 megaparsecs with a high signal-to-noise ratio (about 3.4), implying environment matter density in notable excess of the cosmological mean. Our finding reveals this system to be extremely rare in the current paradigm of structure formation and, implies that enhancing mechanisms around high-mass halos can be very effective. Future lensing surveys will probe the surroundings of single haloes, enabling the study of their formation and evolution of structure.© 2018, The Author(s).We thank J.A.R. Martin for coordinating the spectroscopic campaign and L. D'Avino for suggestions on the rendering of Fig. 1. S.E. and M.S. acknowledge financial support from contracts ASI-INAF I/009/10/0, NARO15 ASI-INAF I/037/12/0, ASI 2015-046-R.0 and ASI-INAF n.2017-14-H.0. C.G. acknowledges support from the Italian Ministry for Education, University, and Research (MIUR) through the SIR individual grant SIMCODE, project number RBSI14P4IH, and the Italian Ministry of Foreign affairs and International Cooperation, Directorate General for Country Promotion for Country Promotion. L.I. acknowledges support from the Spanish research project AYA 2014-58381-P. L.M. acknowledges support from the grants ASI n. I/023/12/0 and PRIN MIUR 2015. A.F., A.S. and R.B. acknowledge financial support from the Spanish Ministry of Economy and Competitiveness (MINECO) under AYA 2014-60438-P, ESP2013-48362-C2-1-P and the 2011 Severo Ochoa Program MINECO SEV-2011-0187 projects. This article includes observations made with the Gran Telescopio Canarias (GTC) operated by Instituto de Astrofisica de Canarias (IAC) with telescope time awarded by the CCI International Time Programme at the Canary Islands observatories (programme ITP13-8). The simulations were run on the Marconi supercomputer at Cineca thanks to the projects IsC10_MOKAlen3 and IsC49_ClBra01

Velocity dispersion vs cluster mass: A new scaling law with The Three Hundred clusters

International audienceThe Planck Collaboration has shown that the number of clusters as a function of their mass and redshift is an extremely powerful tool for cosmological analyses. However, the true cluster mass is not directly measurable. Among the possible approaches, clusters mass could be related to different observables via self similar scaling law. These observables are related to the baryonic components of which a cluster is composed. However, the theoretical relations that allow the use of these proxies often are affected by observational and physical biases, which impacts on the determination of the cluster mass. Fortunately, cosmological simulations are an extremely powerful tool to assess these problems. We present our calibration of the scaling relation between mass and velocity dispersion of galaxy members from the study of the simulated clusters of The Three Hundred project with mass above 1013M⊙. In order to investigate the presence of a redshift dependence, we analyzed 16 different redshifts between z = 0 and z = 2. Finally, we investigated the impact of different AGN feedback models

Morphological analysis of SZ and X-ray maps of galaxy clusters with Zernike polynomials

Several methods are used to evaluate, from observational data, the dynamical state of galaxy clusters. Among them, the morphological analysis of cluster images is well suited for this purpose. We report a new approach to the morphology, which consists in analytically modelling the images with a set of orthogonal functions, the Zernike polynomials (ZPs). We validated the method on mock high-resolution Compton parameter maps of synthetic galaxy clusters from Th

The COVID-19 Infection in Italy: A Statistical Study of an Abnormally Severe Disease

We statistically investigate the Coronavirus Disease 19 (COVID-19) pandemic, which became particularly invasive in Italy in March 2020. We show that the high apparent lethality or case fatality ratio (CFR) observed in Italy, as compared with other countries, is likely biased by a strong underestimation of the number of infection cases. To give a more realistic estimate of the lethality of COVID-19, we use the actual (March 2020) estimates of the infection fatality ratio (IFR) of the pandemic based on the minimum observed CFR and analyze data obtained from the Diamond Princess cruise ship, a good representation of a &ldquo;laboratory&rdquo; case-study from an isolated system in which all the people have been tested. From such analyses, we derive more realistic estimates of the real extent of the infection as well as more accurate indicators of how fast the infection propagates. We then isolate the dominant factors causing the abnormal severity of the disease in Italy. Finally, we use the death count&mdash;the only data estimated to be reliable enough&mdash;to predict the total number of people infected and the interval of time when the infection in Italy could end

Gravitational lensing detection of an extremely dense environment around a galaxy cluster

Galaxy clusters form at the highest-density nodes of the cosmic web. The clustering of dark matter halos hosting these galaxy clusters is enhanced relative to the general mass distribution, with the matter density beyond the virial region being strongly correlated to the halo mass (halo bias). Halo properties other than mass can further enhance the halo clustering (secondary bias). Observational campaigns have ascertained the halo bias, but efforts to detect this secondary bias for massive halos have been inconclusive. Here, we report the analysis of the environment bias in a sample of massive clusters, selected through the Sunyaev-Zel'dovich effect by the Planck mission, focusing on the detection of the environment dark matter correlated to a single cluster, PSZ2 G099.86+58.45. The gravitational lensing signal of the outskirts is very large and can be traced up to 30 megaparsecs with a high signal-to-noise ratio (about 3.4), implying environment matter density in notable excess of the cosmological mean. Our finding reveals this system to be extremely rare in the current paradigm of structure formation and, implies that enhancing mechanisms around high-mass halos can be very effective. Future lensing surveys will probe the surroundings of single haloes, enabling the study of their formation and evolution of structure

The Three Hundred project: The gizmo-simba run

We introduce \textsc{Gizmo-Simba}, a new suite of galaxy cluster simulations within \textsc{The Three Hundred} project. \textsc{The Three Hundred} consists of zoom re-simulations of 324 clusters with $M_{200}\gtrsim 10^{14.8}M_\odot$ drawn from the MultiDark-Planck $N$-body simulation, run using several hydrodynamic and semi-analytic codes. The \textsc{Gizmo-Simba} suite adds a state-of-the-art galaxy formation model based on the highly successful {\sc Simba} simulation, mildly re-calibrated to match $z=0$ cluster stellar properties. Comparing to \textsc{The Three Hundred} zooms run with \textsc{Gadget-X}, we find intrinsic differences in the evolution of the stellar and gas mass fractions, BCG ages, and galaxy colour-magnitude diagrams, with \textsc{Gizmo-Simba} generally providing a good match to available data at $z \approx 0$. \textsc{Gizmo-Simba}'s unique black hole growth and feedback model yields agreement with the observed BH scaling relations at the intermediate-mass range and predicts a slightly different slope at high masses where few observations currently lie. \textsc{Gizmo-Simba} provides a new and novel platform to elucidate the co-evolution of galaxies, gas, and black holes within the densest cosmic environments.Comment: 20 pages, 12 figures, matched to published version in MNRA