Radio halos in a mass-selected sample of galaxy clusters

A fraction of galaxy clusters host Mpc-scale Radio Halos (RH), generated by ultrarelativistic electrons in the magnetized intra cluster medium (ICM). In the current view they trace turbulent regions in merging clusters, where relativistic particles are trapped and accelerated. This model has clear expectations about the statistical properties of RHs. To test these expectations large mass-selected samples of galaxy clusters with adequate radio and X-ray data are necessary. We used the Planck SZ cluster catalogue as suitable starting point of our investigation, selecting clusters with M500>6x10^14 Msun at 0.08

Galaxy evolution in the VIMOS public extragalactic redshift survey (VIPERS)

In this work I present the first measurements of the galaxy stellar mass function (GSMF) from the first public release of the VIPERS catalogue, containing ∼55,000 objects. First, I present the survey design, its scientific goal, the redshift measurements and validation. Then, I provide details about the estimate of galaxy stellar masses, star formation rates, and other physical quantities. I derive the GSMF of different galaxy types (e.g. active and passive galaxies) and as a function of the environment (defined through the local galaxy density contrast). These estimates represent new observational evidence useful to characterise the mechanism of galaxy evolution.

Constraining mass and shape of galaxy clusters through large scale structures

The mass estimation of galaxy clusters is a crucial point for modern cosmology, and can be obtained by several different techniques. In this work we discuss a new method to measure the mass of galaxy clusters connecting the gravitational potential of the cluster with the kinematical properties of its surroundings. We explore the dynamics of the structures located in the region outside virialized cluster, We identify groups of galaxies, as sheets or filaments, in the cluster outer region, and model how the cluster gravitational potential perturbs the motion of these structures from the Hubble fow. This identification is done in the redshift space where we look for overdensities with a filamentary shape. Then we use a radial mean velocity profile that has been found as a quite universal trend in simulations, and we fit the radial infall velocity profile of the overdensities found. The method has been tested on several cluster-size haloes from cosmological N-body simulations giving results in very good agreement with the true values of virial masses of the haloes and orientation of the sheets. We then applied the method to the Coma cluster and even in this case we found a good correspondence with previous. It is possible to notice a mass discrepancy between sheets with different alignments respect to the center of the cluster. This difference can be used to reproduce the shape of the cluster, and to demonstrate that the spherical symmetry is not always a valid assumption. In fact, if the cluster is not spherical, sheets oriented along different axes should feel a slightly different gravitational potential, and so give different masses as result of the analysis described before. Even this estimation has been tested on cosmological simulations and then applied to Coma, showing the actual non-sphericity of this cluster.

Black Hole and Galaxy Growth over Cosmic Time: the Chandra COSMOS Legacy Survey

The study of supermassive black hole (SMBH) accretion during their phase of activity (hence becoming active galactic nuclei, AGN), and its relation to the host-galaxy growth, requires large datasets of AGN, including a significant fraction of obscured sources. X-ray data are strategic in AGN selection, because at X-ray energies the contamination from non-active galaxies is far less significant than in optical/infrared surveys, and the selection of obscured AGN, including also a fraction of heavily obscured AGN, is much more effective. In this thesis, I present the results of the Chandra COSMOS Legacy survey, a 4.6 Ms X-ray survey covering the equatorial COSMOS area. The COSMOS Legacy depth (flux limit f=2x10^(-16) erg/s/cm^(-2) in the 0.5-2 keV band) is significantly better than that of other X-ray surveys on similar area, and represents the path for surveys with future facilities, like Athena and X-ray Surveyor. The final Chandra COSMOS Legacy catalog contains 4016 point-like sources, 97% of which with redshift. 65% of the sources are optically obscured and potentially caught in the phase of main BH growth. We used the sample of 174 Chandra COSMOS Legacy at z>3 to place constraints on the BH formation scenario. We found a significant disagreement between our space density and the predictions of a physical model of AGN activation through major-merger. This suggests that in our luminosity range the BH triggering through secular accretion is likely preferred to a major-merger triggering scenario. Thanks to its large statistics, the Chandra COSMOS Legacy dataset, combined with the other multiwavelength COSMOS catalogs, will be used to answer questions related to a large number of astrophysical topics, with particular focus on the SMBH accretion in different luminosity and redshift regimes.

The relation between mass and concentration in x-ray galaxy clusters at high-redshift.

In this Thesis work we have studied the properties of high-redshift galaxy clusters through the X-ray emission from their intracluster gas. In particular, we have focused on the relation between concentration and mass that is related to the density of the universe at the formation time of the clusters and therefore, it is a powerful cosmological probe. Concentration is expected to be a decreasing function of mass but a complete characterization of this relation has not been reached yet. We have analysed 22 clusters observed withe the Chandra satellite at high redshift and we have investigated the concentration-mass relation.

Non-thermal properties of two galaxy filament candidates from JVLA observations

Large-scale structures can be considered an interesting and useful "laboratory" to better investigate the Universe; in particular the filaments connecting clusters and superclusters of galaxies can be a powerful tool for this intent, since they are not virialised systems yet. The large structures in the Universe have been studied in different bands, in particular the present work takes into consideration the emission in the radio band. In the last years both compact and diffuse radio emission have been detected, revealing to be associated to single objects and clusters of galaxies respectively. The detection of these sources is important, because the radiation process is the synchrotron emission, which in turn is linked to the presence of a magnetic field: therefore studying these radio sources can help in investigating the magnetic field which permeates different portions of space. Furthermore, radio emission in optical filaments have been detected recently, opening new chances to further improve the understanding of structure formation. Filaments can be seen as the net which links clusters and superclusters. This work was made with the aim of investigating non-thermal properties in low-density regions, looking for possible filaments associated to the diffuse emission. The analysed sources are 0917+75, which is located at a redshift z = 0.125, and the double cluster system A399-A401, positioned at z = 0.071806 and z = 0.073664 respectively. Data were taken from VLA/JVLA observations, and reduced and calibrated with the package AIPS, following the standard procedure. Isocountour and polarisation maps were yielded, allowing to derive the main physical properties. Unfortunately, because of a low quality data for A399-A401, it was not possible to see any radio halo or bridge.

Connection between x-ray and radio properties of cool-core galaxy clusters hosting radio mini-halos

Gli ammassi di galassie sono gli oggetti gravitazionalmente legati più grandi dell’Universo. Questi emettono principalmente in banda X tramite bremsstrahlung. Una frazione mostra anche emissione radio diffusa da parte di elettroni relativistici che spiraleggiano nel campo magnetico. Si possono classificare tre tipi di emissione: alon, relitti e mini-aloni radio (MH). I MH sono sorgenti radio su scale di ≥ 200 – 500 kpc, osservate al centro di ammassi caratterizzati dalla presenze di cool-core (CC). L’origine dei MH non è ancora chiara. Gli elettroni relativistici che emettono in banda radio hanno tempi di vita radiativi di molto inferiori a quelli necessari per diffondere sulle scale dell’emissione diffusa. Quindi non sono semplicemente iniettati dalle galassie presenti negli ammassi ed è necessario un meccanismo di accelerazione “in-situ” nell’ICM. I MH testimoniano la presenza di meccanismi che canalizzano parte del budget energetico disponibile nei CC nell’ICM.Quindi lo studio è importante per comprendere la fisica dell’ICM e l’interazione fra le componenti non termiche e termiche. I MH si formano attraverso la riaccelerazione delle particelle relativistiche ad opera della turbolenza del gas. L’origine di questa turbolenza tuttavia non è ancora ben compresa. Gli ammassi CC sono caratterizzati da un picco della brillanza X nelle regioni centrali e da un drop della temperatura verso il centro accompagnata da aumento della densità del gas. Si ritiene che questo sia dovuto al raffreddamento del gas che quindi fluisce nelle zone centrali. Recenti osservazioni in X risultan inconsistenti con il modello classico di CF, suggerendo la presenza di una sorgente di riscaldamento del gas su scale del core degli ammassi. Recentemente Zhuravleva (2014) hanno mostrato che il riscaldamento dovuto alla turbolenza prodotta dall'AGN centrale è in grado di bilanciare il processo di raffreddamento. Abbiamo assunto che la turbolenza responsabile del riscaldamento del gas è anche responsabile dell’accelerazione delle particelle nei MH. Nell’ambito di questo scenario ci si aspetta una correlazione tra la potenza del cooling flow, PCF, che è una misura del tasso di energia emessa dal gas che raffredda nei CC, e la luminosità radio, che è una frazione dell’energia della turbolenza che è canalizzata nell’accelerazione delle particelle. In questo lavoro di tesi abbiamo utilizzato il più grande campione disponibile di MH, allo scopo di studiare la connessione fra le proprietà dei MH e quelle del gas termico nei core degli ammassi che li ospitano. Abbiamo analizzato i dati di 21 ammassi e ricavato i parametri fisici all’interno del raggio di cooling e del MH. Abbiamo ricavato la correlazione fra luminosità radio, e PCF. Abbiamo trovato che le due quantità correlano in modo quasi-lineare confermando i risultati precedenti. Tale correlazione suggerisce uno stretto legame fra le proprietà del gas nei CC e l’origine dei MH.

Radio relics and magnetic fields in galaxy clusters

Radio relics are diffuse synchrotron sources generally located in the peripheries of galaxy clusters in merging state. According to the current leading scenario, relics trace gigantic cosmological shock waves that cross the intra-cluster medium where particle acceleration occurs. The relic/shock connection is supported by several observational facts, including the spatial coincidence between relics and shocks found in the X-rays. Under the assumptions that particles are accelerated at the shock front and are subsequently deposited and then age downstream of the shock, Markevitch et al. (2005) proposed a method to constrain the magnetic field strength in radio relics. Measuring the thickness of radio relics at different frequencies allows to derive combined constraints on the velocity of the downstream flow and on the magnetic field, which in turns determines particle aging. We elaborate this idea to infer first constraints on magnetic fields in cluster outskirts. We consider three models of particle aging and develop a geometric model to take into account the contribution to the relic transverse size due to the projection of the shock-surface on the plane of the sky. We selected three well studied radio relics in the clusters A 521, CIZA J2242.8+5301 and 1RXS J0603.3+4214. These relics have been chosen primarily because they are almost seen edge-on and because the Mach number of the shock that is associated with these relics is measured by X-ray observations, thus allowing to break the degeneracy between magnetic field and downstream velocity in the method. For the first two clusters, our method is consistent with a pure radiative aging model allowing us to derive constraints on the relics magnetic field strength. In the case of 1RXS J0603.3+4214 we find that particle life-times are consistent with a pure radiative aging model under some conditions, however we also collect evidences for downstream particle re-acceleration in the relic W-region and for a magnetic field decaying downstream in its E-region. Our estimates of the magnetic field strength in the relics in A 521 and CIZA J2242.8+5301 provide unique information on the field properties in cluster outskirts. The constraints derived for these relics, together with the lower limits to the magnetic field that we derived from the lack of inverse Compton X-ray emission from the sources, have been combined with the constraints from Faraday rotation studies of the Coma cluster. Overall results suggest that the spatial profile of the magnetic field energy density is broader than that of the thermal gas, implying that the ε_th /ε_B ratio decreases with cluster radius. Alternatively, radio relics could trace dynamically active regions where the magnetic field strength is biased high with respect to the average value in the cluster volume.

Action-based dynamical models of the Fornax dwarf spheroidal galaxy

Il lavoro presentato in questa Tesi si basa sul calcolo di modelli dinamici per Galassie Sferoidali Nane studiando il problema mediante l'utilizzo di funzioni di distribuzione. Si è trattato un tipo di funzioni di distribuzione, "Action-Based distribution functions", le quali sono funzioni delle sole variabili azione. Fornax è stata descritta con un'appropriata funzione di distribuzione e il problema della costruzione di modelli dinamici è stato affrontato assumendo sia un alone di materia oscura con distribuzione di densità costante nelle regioni interne sia un alone con cuspide. Per semplicità è stata assunta simmetria sferica e non è stato calcolato esplicitamente il potenziale gravitazionale della componente stellare (le stelle sono traccianti in un potenziale gravitazionale fissato). Tramite un diretto confronto con alcune osservabili, quali il profilo di densità stellare proiettata e il profilo di dispersione di velocità lungo la linea di vista, sono stati trovati alcuni modelli rappresentativi della dinamica di Fornax. Modelli calcolati tramite funzioni di distribuzione basati su azioni permettono di determinare in maniera autoconsistente profili di anisotropia. Tutti i modelli calcolati sono caratterizzati dal possedere un profilo di anisotropia con forte anisotropia tangenziale. Sono state poi comparate le stime di materia oscura di questi modelli con i più comuni e usati stimatori di massa in letteratura. E stato inoltre stimato il rapporto tra la massa totale del sistema (componente stellare e materia oscura) e la componente stellare di Fornax, entro 1600 pc ed entro i 3 kpc. Come esplorazione preliminare, in questo lavoro abbiamo anche presentato anche alcuni esempi di modelli sferici a due componenti in cui il campo gravitazionale è determinato dall'autogravità delle stelle e da un potenziale esterno che rappresenta l'alone di materia oscura.

Galactic fountain flows in high-resolution hydrodynamical simulations of galaxy disks

Feedback from the most massive components of a young stellar cluster deeply affects the surrounding ISM driving an expanding over-pressured hot gas cavity in it. In spiral galaxies these structures may have sufficient energy to break the disk and eject large amount of material into the halo. The cycling of this gas, which eventually will fall back onto the disk, is known as galactic fountains. We aim at better understanding the dynamics of such fountain flow in a Galactic context, frame the problem in a more dynamic environment possibly learning about its connection and regulation to the local driving mechanism and understand its role as a metal diffusion channel. The interaction of the fountain with a hot corona is hereby analyzed, trying to understand the properties and evolution of the extraplanar material. We perform high resolution hydrodynamical simulations with the moving-mesh code AREPO to model the multi-phase ISM of a Milky Way type galaxy. A non-equilibrium chemical network is included to self consistently follow the evolution of the main coolants of the ISM. Spiral arm perturbations in the potential are considered so that large molecular gas structures are able to dynamically form here, self shielded from the interstellar radiation field. We model the effect of SN feedback from a new-born stellar cluster inside such a giant molecular cloud, as the driving force of the fountain. Passive Lagrangian tracer particles are used in conjunction to the SN energy deposition to model and study diffusion of freshly synthesized metals. We find that both interactions with hot coronal gas and local ISM properties and motions are equally important in shaping the fountain. We notice a bimodal morphology where most of the ejected gas is in a cold $10^4$ K clumpy state while the majority of the affected volume is occupied by a hot diffuse medium. While only about 20\% of the produced metals stay local, most of them quickly diffuse through this hot regime to great scales.

Measuring energy spectra of TeV gamma-ray emission from the Cygnus region of our galaxy with Milagro

High energy gamma rays can provide fundamental clues to the origins of cosmic rays. In this thesis, TeV gamma-ray emission from the Cygnus region is studied. Previously the Milagro experiment detected five TeV gamma-ray sources in this region and a significant excess of TeV gamma rays whose origin is still unclear. To better understand the diffuse excess the separation of sources and diffuse emission is studied using the latest and most sensitive data set of the Milagro experiment. In addition, a newly developed technique is applied that allows the energy spectrum of the TeV gamma rays to be reconstructed using Milagro data. No conclusive statement can be made about the spectrum of the diffuse emission from the Cygnus region because of its low significance of 2.2 σ above the background in the studied data sample. The entire Cygnus region emission is best fit with a power law with a spectral index of α=2.40 (68% confidence interval: 1.35-2.92) and a exponential cutoff energy of 31.6 TeV (10.0-251.2 TeV). In the case of a simple power law assumption without a cutoff energy the best fit yields a spectral index of α=2.97 (68% confidence interval: 2.83-3.10). Neither of these best fits are in good agreement with the data. The best spectral fit to the TeV emission from MGRO J2019+37, the brightest source in the Cygnus region, yields a spectral index of α=2.30 (68% confidence interval: 1.40-2.70) with a cutoff energy of 50.1 TeV (68% confidence interval: 17.8-251.2 TeV) and a spectral index of α=2.75 (68% confidence interval: 2.65-2.85) when no exponential cutoff energy is assumed. According to the present analysis, MGRO J2019+37 contributes 25% to the differential flux from the entire Cygnus at 15 TeV.

OPPL-Galaxy, a Galaxy tool for enhancing ontology exploitation as part of bioinformatics workflows

Biomedical ontologies are key elements for building up the Life Sciences Semantic Web. Reusing and building biomedical ontologies requires flexible and versatile tools to manipulate them efficiently, in particular for enriching their axiomatic content. The Ontology Pre Processor Language (OPPL) is an OWL-based language for automating the changes to be performed in an ontology. OPPL augments the ontologists’ toolbox by providing a more efficient, and less error-prone, mechanism for enriching a biomedical ontology than that obtained by a manual treatment. Results We present OPPL-Galaxy, a wrapper for using OPPL within Galaxy. The functionality delivered by OPPL (i.e. automated ontology manipulation) can be combined with the tools and workflows devised within the Galaxy framework, resulting in an enhancement of OPPL. Use cases are provided in order to demonstrate OPPL-Galaxy’s capability for enriching, modifying and querying biomedical ontologies. Conclusions Coupling OPPL-Galaxy with other bioinformatics tools of the Galaxy framework results in a system that is more than the sum of its parts. OPPL-Galaxy opens a new dimension of analyses and exploitation of biomedical ontologies, including automated reasoning, paving the way towards advanced biological data analyses.

Can Jupiters be found by monitoring Galactic bulge microlensing events from northern sites?

In 1998 the EXPORT team monitored microlensing event light curves using a charge-coupled device (CCD) camera on the IAC 0.8-m telescope on Tenerife to evaluate the prospect of using northern telescopes to find microlens anomalies that reveal planets orbiting the lens stars. The high airmass and more limited time available for observations of Galactic bulge sources make a northern site less favourable for microlensing planet searches. However, there are potentially a large number of northern 1-m class telescopes that could devote a few hours per night to monitor ongoing microlensing events. Our IAC observations indicate that accuracies sufficient to detect planets can be achieved despite the higher airmass.

Enhanced reproducibility of SADI web service workflows with Galaxy and Docke

Background: Semantic Web technologies have been widely applied in the life sciences, for example by data providers such as OpenLifeData and through web services frameworks such as SADI. The recently reported OpenLifeData2SADI project offers access to the vast OpenLifeData data store through SADI services. Findings: This article describes how to merge data retrieved from OpenLifeData2SADI with other SADI services using the Galaxy bioinformatics analysis platform, thus making this semantic data more amenable to complex analyses. This is demonstrated using a working example, which is made distributable and reproducible through a Docker image that includes SADI tools, along with the data and workflows that constitute the demonstration. Conclusions: The combination of Galaxy and Docker offers a solution for faithfully reproducing and sharing complex data retrieval and analysis workflows based on the SADI Semantic web service design patterns.