Studio e Lavoro > Tesi di laurea

Recently, Dietl et al. (2024) detected and studied an X-ray filament with a length of over 13 Mpc connecting two galaxy clusters: Abell 3667 and Abell 3651. This is the first individual filament observed between two galaxy clusters that are significantly separated, and it is clearly located outside the intracluster medium. The system is in the southern hemisphere with a redshift of z=0.05-0.06 and has already been observed as part of the Polarization Sky Survey of the Universe Magnetism (POSSUM), a survey that will soon be made public and will significantly enhance our understanding of cosmic magnetic fields.

The goal of the thesis will be to use the catalog of polarized sources and their Faraday rotation data from the POSSUM survey to study the magnetic field of this newly detected filament. Specifically, the student will analyze, on a statistical basis, the differences in Faraday rotation dispersion between the galaxy clusters, the filaments, and the background, in order to estimate the magnetic field in this region.

The student will use 1-4 GHz observations of the CIZA J2242.8+5301, the famous cluster hosting the Sausage radio relic, performed with the Jansky Very Large Array (JVLA). The total intensity and polarized emission of cluster radio galaxies will be modeled using the QU-fitting and the RM-synthesis approach. Subsequently, the obtained information will be compared with semi-analytical and/or cosmological simulations of galaxy clusters in order to derive the magnetic field properties for this famous galaxy cluster. The student will develop important coding skills using different programming languages (python and IDL).

Within this context, we propose a Master Thesis aiming to explore how polycyclic aromatic hydrocarbons (PAHs), emitting in the mid-IR band and commonly used as indicators of star formation activity, can be used as a proxy to estimate molecular gas content in nearby galaxies. This thesis will be based on the DustPedia project, which is definitively characterizing the dust properties in the Local Universe by exploiting a database of multi-wavelength imagery and photometry that greatly exceeds the scope (in terms of wavelength coverage and number of galaxies) of any similar survey (Davies et al. 2017; Casasola et al. 2017, 2020, 2022). The DustPedia sample consists of 875 extended (D₂₅ > 1′) galaxies of all morphological types, at distances < 40 Mpc (z < 0.01). The rich DustPedia database contains maps and photometry from UV to sub-mm bands (41 bands, on average, per galaxy), in addition to millimeter CO data tracing molecular gas.

By exploiting the DustPedia sample and database, the student will explore global and spatially resolved relationships between PAH (traced at 8 and 12 micron) and CO emission, taking into consideration their mutual correlation with star-formation rate, with the ultimate aim of offering new, improved empirical predictors of molecular gas content based on PAH emission and star formation activity. This topic is especially timely in light of the enormous improvements in mid-IR science that are emerging from the revolutionary James Webb Space Telescope.

The student will analyze observations taken with the Hydrogen Epoch of Reionization Array, a custom-built radio interferometric arrays that observes the 21 cm line in the 6 < z < 30 range. The student will work on the data calibration and foreground separation with the ultimate goal of improving the current 21 cm power spectrum, providing a better constraint on the physical properties of the first stars and galaxies – e.g., the average mass of the dark matter halo where they formed, their X-ray properties, how their star formation process started and evolve with time.

The thesis will consist in the analysis of the available data from Large-aperture Experiment to Detect the Dark Age (LEDA), located in Owens Valley in California, and/or simulations of the Radio Experiment for the Analysis of Cosmic Hydrogen (REACH), deployed in the Karoo radio reserve in South Africa. Both experiments aim to measure the sky-averaged 21 cm signal in the 12 < z < 30 range.

The analysis will include the development of techniques to disentangle the signal from the much stronger Galactic and extra-galactic foregrounds and the characterization of the impact of the systematic effects.

As IM observations trace the underlying matter distribution of the Universe on large scales, a 21 cm detection would place tight constraints on cosmological parameters.

The student will take an active part in the MeerKLASS IM survey of the MeerKAT radio telescope.  The MeerKLASS data cover a  300~deg^2 sky patch with the goal to observe IM up to z ~ 0.4 and new data will be available soon. Thesis activities will include (but not necessarily limited to) data analysis, foreground separation, and simulations of the expected cosmological signal.

Our overall project consist in the systematic, multi-scale, multi-phase analysis of a volume-limited sample of typical local RGs. For the Thesis, the student will specifically focus on the analysis of the cold gas component in some sample sources using recently-acquired HI data from the Australia Telescope Compact Array (ATCA) and/or molecular gas (CO) data from the Atacama millimetre/sub-millimetre array (ALMA). In all the cases, the goal will be to study the cold gas distribution and kinematics, with a special focus on looking for signatures of external gas accretion with HI data and investigating inflows and outflows at pc scales with CO data.

By carrying out this project, the student will learn how to properly use softwares for the reduction and analysis of interferometric data (e.g. CASA) and tools for studying the gas distribution and kinematics (e.g. 3DBarolo, KinMS), as well as deal with multi-wavelength data from some of the most powerful facilities currently operating at mm and radio wavelengths. All the data will be provided fully calibrated, with also some basic imaging performed. For this work, basic knowledge in radio interferometry and Python would be desirable.

A novel interpretation has been suggested that several of these radio sources reside in double systems in different phases of their merging evolution with rapidly precessing jets which are unable to escape the inner region of the host galaxy.

The implication for this scenario is a transverse motion of the hot-spots respect the center of activity, in contrast with the reported evidence of proper motions of the hot spots expanding outwards. Indeed, some transverse motions have been already detected, and many of the reported expansion speeds need to be revised.

The thesis will consist in data reduction and analysis of VLBI data taken in various epochs for selected GPS radio sources, to possibly find new evidence for transverse motions of the hot-spots, and bring support to the precessing jet scenario.

(ii) probe the structure of the jet (pc to kpc scales);

(iii) determine the physical properties and variability in >10 years, potentially detecting proper motions – if so, it would be the most distant proper motion ever detected and can be used to infer q0;

(iv) use the results to make predictions for the next generation of radio telescopes (i.e. SKA and ngVLA).

This thesis project focuses on FBOT AT2018cow, which is thus far the nearest (60 Mpc) and best studied target with a rich multi-wavelength dataset. In particular, the student will work on a new deep X-ray observation taken about 6 yr after the transient discovery, with the goal to: (i) map the long-term evolution and spectrum in X-rays of this enigmatic source and (i) shed light on the possible connection of FBOTs with manifestations of super-Eddington accretion on BHs.

This thesis builds on the results of a previous UniBO master’s thesis, in which a Software to calculate the geometric coefficients for telescope pointing was developed. The proposed work will complete and extend that study by focusing on instrumental calibration.

The overall work consists of the following main activities:

• Study calibration procedures for interferometers and beamformers;
• Implementation and optimization of instrumental calibration software in Python;
• Comparison with the currently used MATLAB code;
• Perform observational tests to validate algorithms and characterize the array beam.

For this work, basic to intermediate programming skills in Python and MATLAB are required.