Simulating mock observations for weak lensing analysis and galaxy clusters mass estimates

The purpose of this thesis is learning how to accomplish a weak lensing analysis and estimate the mass of a galaxy cluster. For this task, I performed simulations in order to obtain mock observations with the Subaru Telescope of galaxies distorted by a massive galaxy cluster. Their distortion was quantified according to the Kaiser-Squires-Broadhurst (KSB) method. Chapter 1 is an introduction to crucial concepts regarding this thesis, in the fields of cosmology, galaxy clusters and gravitational lensing. Chapter 2 discusses the process of the simulation, its inputs and outputs and the analysis of the distortion of galaxy shapes. Chapter 3 regards the results of the analysis on the real galaxy cluster MACS J1206, the comparison with its model and how to get its mass by means of a fit with a Navarro-Frenk-White (NFW) mass distribution. Chapter 4 reports the application of the same analysis to MACS J1206 observed in different filters and two simulated clusters: Ares and Hera. Chapter 5 sums up the key points of the whole work

Cosmology with clusters of galaxies in the eROSITA era

The nature of dark matter and dark energy is one of the most intriguing scientific questions of this century. Tiny density perturbations in the early Universe evolved under the action of gravity, growing into the structures we see nowadays, such as galaxies and clusters. Such growth throughout cosmic time depends on the nature and abundance of these mysterious dark components. Clusters of galaxies provide a great tool for studying the cosmological evolution of the Universe. Galaxy clusters are the most massive virialized objects in the Universe, they reside in the nodes of the cosmic web, and are a direct tracer of the large scale structure of the Universe. Their abundance as a function of mass and redshift (the halo mass function) provides a stringent test for different cosmological models and tight constraints on the total amount of matter and the amplitude of the density perturbations in the Universe, but it also depends on the nature of dark energy. The eROSITA X-ray telescope will provide the largest X-ray-selected sample of galaxy clusters ever, with the potential of studying dark matter and dark energy with unprecedented precision. A detailed understanding of the sources detected by eROSITA and the uncertainties in the data is fundamental to reach this goal. The first aim of this thesis is to produce and study a digital twin of the first eROSITA all-sky survey (eRASS1), to characterize the source catalog and test the science pipelines. We use state of the art models to predict the X-ray emission from clusters of galaxies and AGN, and model the X-ray background using real data as a starting point. With this setup, we run an X-ray software simulator to produce mock detected photons, accounting for technical details such as the instrument response and the observation strategy. We run the eROSITA Standard Analysis Software System (eSASS), which produces a source catalog with very similar properties to the one obtained from real data. We match the input and output catalogs with an accurate algorithm based on the origin of each photon. We detect all the brightest clusters and AGN in the simulation. The fraction of detected sources primarily depends on flux and exposure time. Secondary effects, such as the source size and the central emissivity, are relevant for clusters. We provide a detailed study of the trade-off between completeness and purity. We find that progressive thresholds of detection likelihood get rid of the background fluctuations in the source catalog, while cuts in extension likelihood are necessary to remove bright point sources contaminating the cluster sample. We discuss different selections according to a given science goal. For example, the inclusion of the majority of sources in the sample is best, if one wants to find interesting objects to study the astrophysics of faint clusters and groups. Instead, a more secure cluster sample with low contamination is required for a cosmological experiment. Once the cluster sample is selected, accurate halo mass function models are key to reaching precise constraints on cosmological models. The second aim of this thesis is to calibrate a model of the mass function that also includes variables related to the dynamical state of dark matter halos. We use the dark matter-only MultiDark suite of simulations and the high-mass objects hosting clusters of galaxies therein. We measure the mean relations of concentration, offset parameter (Xoff ), and spin as a function of dark matter halo mass and redshift. We investigate the distributions around the mean relations. We confirm the recent discovery of the concentration upturn at high masses and provide a model that predicts the concentration for different values of mass and redshift with one single equation. We find that the concentration of low-mass halos shows a faster redshift evolution compared to high-mass halos, especially in the high-concentration regime. We find that the offset parameter is systematically smaller at low redshift, in agreement with the relaxation of structures at recent times. The individual models are combined into a comprehensive framework, which predicts the mass function as a function of spin and offset. Our model recovers the fiducial mass function with great accuracy at redshift 0 and accounts for redshift evolution up to z ∼ 1.5. The generalized mass function framework allows marginalizing over selection effects related to the dynamical state of dark matter halos in a cluster count experiment. However, a link between observations and theoretical models is lacking. The third goal of this thesis is to study the dynamical state of clusters detected by eROSITA using the offset between the X-ray and the optical centers. We aim to connect the offset measured in eROSITA observations to predictions by hydrodynamical simulations and N-body models, assessing the astrophysical effects affecting the displacements. We measure the offset for clusters observed in the eROSITA Final Equatorial-Depth Survey (eFEDS) and eRASS1. We focus on a subsample of 87 massive eFEDS clusters at low redshift. We compare the displacements in this sample to those predicted by the TNG and the Magneticum simulations. We link the observations to the offset parameter Xoff measured for dark matter halos in N-body simulations, using the hydrodynamical simulations as a bridge. We find that on average the eFEDS clusters show a smaller offset compared to eRASS1 because the latter contains a larger fraction of massive and disturbed structures. The offset measured in the eFEDS subsample is in agreement with the predictions from TNG and Magneticum, and the distribution of the offset parameter from dark matter only simulations. However, the tails of the distributions are different. Baryonic effects cause a decrement (increment) in the low (high) offset regime compared to the Xoff distribution from dark matter-only simulations. Finally, we find a correlation between the offset predicted by hydro simulations and Xoff measured in their parent dark matter-only run and calibrate a relation between them, which allows us to recover the full Xoff distribution with excellent precision. The work developed in this thesis is essential to characterize the real eRASS1 sample, hat will soon be available to the public. The development of the innovative mass function framework and its link to data with the offset between different definitions of the cluster center will allow the minimization of uncertainties in cluster count experiments due to selection effects related to the cluster dynamical state

A REGIONAL-SCALE ROCK GLACIER INVENTORY IN TRENTINO(ITALIAN ALPS)

none6A number of rock glacier inventories were implemented in the framework of PermaNET (Permafrost long-term monitoring network), a project part of the European Territorial Cooperation and co-funded by the European Regional Development Fund (ERDF) in the scope of the Alpine Space Programme (www.alpine-space.eu). Rock glaciers are regarded as one of the most prominent permafrost-related landforms in the alpine territories. A new statistical model and a permafrost distribution map for the entire Alps are partly based on the rock glacier inventories carried out within the project and, in this framework, a new inventory was completed also in the province of Trento. This region is located in the southern part of the Alps and 20% of its territory lies above an altitude of 2000 m a.s.l. The rock glacier inventory is based on analyses carried out in a GIS using a recent (2006) orthophoto (resolution of 0.5m) and a DEM (grid resolution of 2m). First, the rock glaciers were identified using i) the orthophotos and ii) an hillshade derived from the DEM. Then, the outline of the landforms were digitized in the GIS as polygon shapes. The characteristics of the rock glaciers were included in an attribute table linked to the shapes. Our database consist of several descriptive parameters, including that of the Permafrost Evidences Database (PED) of the PermaNET project. However, in agreement with other project partner (e.g. ARPA Valle d'Aosta), we used a number of supplementary parameters, in order to achieve a more complete description of the landforms. The database was partially filled in during the landform digitalization, but most of the information (particularly the morphometric parameters) were obtained from analyses performed in the GIS. In summary, a first group of descriptive parameters of each rock glacier include: location (mountain group and coordinates), altitude (mean and range), slope, length, width, perimeter and area. Other parameters describe additional characteristics, such as: geometry (lobate or tongue shape); general morphology (simple, complex); surface morphology (presence of longitudinal and transverse ridges and furrows and/or hollows and pits); lithology of the feeding area; debris source (talus, till); degree of vegetation coverage, relationships with the local vegetation boundaries and with the glaciers/perennial snowfields located above the rock glacier. Particular attention was paid to the definition of the activity status of the rock glaciers, that were classified as intact (active and inactive landforms containing frozen material) or relict (landforms without frozen material). The assessment was based on i) several evidences visible in the orthophotos and in the DEM, ii) direct field observations carried out in our previous works and iii) field data (i.e. topographic surveys). We used particularly restrictive criteria for classifying the activity status of the rock glaciers from the orthophotos, and this may have resulted in a slightly lower percentage of intact landforms compared to other inventories. Our inventory includes a total of 705 rock glaciers, 134 (19%) classified as intact, the others as relict. They are located at an average altitude 2280 m a.s.l., with a considerable distinction between relict (average altitude of 2190 m a.s.l.) and intact (average altitude of 2660 m a.s.l.) landforms. 50.3% of the rock glaciers face towards N, NE and NW, while 35.2% face towards S, SE and SW. The landforms density (n of rock glacier/km2) is notably different in the various mountain groups of the province, and this seems to be related to the different lithologies that characterize the region. The average surface of the rock glaciers is about 4.7 hectares (0.047 km2). The total area covered by the rock glaciers (33.3 km2) is 1.2% of the entire area of the province located above 1500 m a.s.l., indicating as these landforms are prominent in the periglacial environment of this region.noneSEPPI R.; CARTON A.; ZUMIANI M.; DALL'AMICO M.; ZAMPEDRI G.; RIGON R.Seppi, R.; Carton, Alberto; Zumiani, M.; Dall'Amico, M.; Zampedri, G.; Rigon, R

Osservazioni e studi sul permafrost in Trentino: il progetto PermaNET

Nell’articolo sono presentate le attività di ricerca svolte sul permafrost in Trentino e i principali risultati del progetto PermaNET (Permafrost Long-term Monitoring Network). Sono stati realizzati un catasto dei rock glacier e una carta dell’indice di diffusione del permafrost derivata da un nuovo modello statistico della sua localizzazione. Inoltre, sono state avviate numerose attività di monitoraggio: tra queste, sono in corso misure di temperatura della superficie del suolo e sono proseguite misure topografiche per quantificare lo spostamento di due rock glacier attivi. Sono stati inoltre attrezzati due siti per la misura della temperatura del sottosuolo e dei parametri climatici esterni, allo scopo di valutare la condizione termica del permafrost in funzione dei cambiamenti climatici. La collaborazione al progetto ha consentito di migliorare considerevolmente la conoscenza di questo importante aspetto dell’ambiente alpino del Trentino

Case studies in the European Alps – Maroccaro rock glacier, Val di Genova, Italian Alps

In 2001 we started a topographic study on an active rock glacier (named Maroccaro rock glacier, acronym MaRG, coordinates: 46° 13’ 06” N, 10° 34’ 34” E) located in the Adamello-Presanella massif (Central Italian Alps). Since 2004, also the near-surface ground temperature was measured using a miniature data logger. Our data show that in eight years (2001-2009) MaRG has moved downslope with average velocities ranging from 0.02 to 0.21 m/year. The velocity reaches a maximum in the middle and the lower part of the rock glacier, and decreases towards the upper sector, where the surveyed boulders are almost stationary. A considerable different velocity from year to year has been observed, but no clear trends seem to emerge from the mean annual displacement rate. On the rock glacier the evolution of the ground temperature since 2004 is directly associated with the air temperature and the snow conditions, in terms of thickness and duration of the snowpack. The ground has warmed significantly both in 2007, after a very mild and little snowy winter, and in 2009, after a cold but exceptionally snowy winter. The displacement rate of MaRG seems to rapidly react to the ground temperature variations, apparently without any time delay. The exceptionally snowy winter 2008/09 seems to have played a significant role on the displacement rate, causing a ground temperature increase and, probably, an increase in velocity, which reached its maximum in that year

Case studies in the European Alps – Amola rock glacier, Val d'Amola, Italian Alps

Topographic measurements are in progress since 2001 on a glacier-derived, active rock glacier (named Amola rock glacier, acronym AmRG, coordinates: 46° 12’ 09” N, 10° 42’ 46” E) located in the Adamello-Presanella group, Central Italian Alps. In addition, data on the ground temperature measured few centimetres below the surface are available since 2004. The displacement data show that some areas of the rock glacier currently (2001-2009) move with velocities ranging from 10 to 20 cm/year, while other sectors can be defined as “dynamically inactive”. The average velocity is significantly variable from year to year, ranging from a minimum of 0.06 m/year (2007-2008) to a maximum of 0.13 m/year (2006-2007), and a slowing trend has been recorded in the last two years. In 2006-2007 a higher rate of displacement seems to be related to a rise in the mean air temperature that probably caused a corresponding rise in the ground temperature. However, in the last year of measurements (2008-2009), an increase in the ground temperature caused by the large amount of snow of the preceding winter, did not result in a corresponding increase of the displacement rate. The dynamic behaviour of this rock glacier reacts very fast to the external forcing, and its response seems to be modulated by the amount and evolution of the snow during winter, due to its effect on the ground temperature. Thus, not only the temperature but also the projected changes in the amount and distribution of precipitation, especially as snow, should be taken into account in assessing the response of this landform to future climate change

The SRG/eROSITA All-Sky Survey: Weak-Lensing of eRASS1 Galaxy Clusters in KiDS-1000 and Consistency Checks with DES Y3 & HSC-Y3

International audienceWe aim to participate in the calibration of the X-ray photon count rate to halo mass scaling relation of galaxy clusters selected in the first eROSITA All-Sky Survey on the Western Galactic Hemisphere (eRASS1) using KiDS-1000 weak-lensing (WL) data. We measure the radial shear profiles around eRASS1 galaxy clusters using background galaxies in KiDS-1000, as well as the cluster member contamination. Furthermore we provide consistency checks with the other stage-III WL surveys who take part in the eRASS1 mass calibration, DES Y3 and HSC-Y3. We determine the cluster member contamination of eRASS1 clusters present in KiDS-1000 based on source number density profiles, where we account for the obscuration caused by cluster galaxies. The extracted shear profiles, together with the contamination model and the lens sample selection, are then analysed through a Bayesian population model. We calibrate the WL mass bias parameter by analysing realistic synthetic shear profiles from mock cluster catalogues. Our consistency checks between KiDS-1000 and DES Y3 & HSC-Y3 include the comparison of contamination-corrected density contrast profiles employing the union of background sources around common clusters, as well as the individual scaling relation results. We present a global contamination model for eRASS1 clusters in KiDS-1000 and the calibration results of the X-ray photon count rate to halo mass relation. The results of the WL mass bias parameter show that the uncertainty of the multiplicative shear bias dominates the systematic error budget at low clusters redshifts while the uncertainty of our contamination model does at high ones. The cross-checks between the three WL surveys show that they are statistically consistent with each other. This enables for the first time cosmological constraints from clusters calibrated by three state-of-the-art WL surveys. (abridged

Full-sky photon simulation of clusters and active galactic nuclei in the soft X-rays for eROSITA

International audienceThe eROSITA X-ray telescope on board the Spectrum-Roentgen-Gamma (SRG) mission will measure the position and properties of about 100,000 clusters of galaxies and 3 million active galactic nuclei over the full sky. To study the statistical properties of this ongoing survey, it is key to estimate the selection function accurately. We create a set of full sky light-cones using the MultiDark and UNIT dark matter only N-body simulations. We present a novel method to predict the X-ray emission of galaxy clusters. Given a set of dark matter halo properties (mass, redshift, ellipticity, offset parameter), we construct an X-ray emissivity profile and image for each halo in the light-cone. We follow the eROSITA scanning strategy to produce a list of X-ray photons on the full sky. We predict scaling relations for the model clusters, which are in good agreement with the literature. The predicted number density of clusters as a function of flux also agrees with previous measurements. Finally, we obtain a scatter of 0.21 (0.07, 0.25) for the X-ray luminosity -- mass (temperature -- mass, luminosity -- temperature) model scaling relations. We provide catalogues with the model photons emitted by clusters and active galactic nuclei. These catalogues will aid the eROSITA end to end simulation flow analysis and in particular the source detection process and cataloguing methods