Probing the intracluster medium at high angular resolution via radio-interferometric measurements of the Sunyaev-Zeldovich effect

The work presented in this thesis is devoted to investigating the physics of galaxy clusters through the characterization of their Sunyaev-Zeldovich (SZ) effect signal observed by the Atacama Large Millimeter/Submillimeter Array (ALMA) and the Atacama Compact Array (ACA). The unparalleled capabilities of ALMA+ACA have definitely opened a millimeter-wave window on the physics of the intracluster medium. The pioneering observations of the SZ effect over scales of a few arcseconds demonstrated that ALMA+ACA can effectively provide a new observational tool, complementary to the more traditional X-ray observations, for probing the physical and thermodynamic state of the intracluster medium down to the smallest physical scales. Central for employing ALMA+ACA to map SZ structures are its outstanding sensitivity and angular resolving power. However, ALMA+ACA currently offers no sensitivity to any signal extending on scales larger than 1-2 arcminutes, as such information is severely filtered out through the interferometric response. A radio-interferometer can in fact provide measurements of signals with angular sizes solely corresponding to the inverse of the lengths of the individual baselines within the array. It follows that the pair of antennae at the smallest distance within an interferometer poses a hard limit on the maximum scale recoverable in a given observation. As galaxy clusters cover scales often larger than the field of view of ALMA, the result is a heavily high-pass filtered view of their SZ signature. In turn, both the proper interpretation of the reconstructed images and the analysis of the raw data become non trivial. To overcome the issue related to the large-scale filtering effect inherent to ALMA, it is key to combine the high-resolution ALMA+ACA measurements with complementary data or information. One possibility to tackle the lack of information on large scales is to consider SZ measurements from single-dish facilities. In fact, single-dish measurements generally have angular resolutions lower than radio-interferometric ones, but can recover sufficiently large angular scales to constrain the total SZ flux from a galaxy cluster. The reconstruction of the SZ signal from the joint analysis of radio-interferometric and single observations can thus be used to get insights into the physical state of small-scale structures within the intracluster medium as well as its global properties. The rich availability of SZ measurements of the renowned galaxy cluster RX J1347.5-1145 offered the opportunity to test such joint modelling approach. As the SZ effect provides information on the line-of-sight integral of the electron pressure distribution within a cluster, the joint study allowed to get a model of the intracluster pressure over an outstanding range of scales. Through the comparison with an independent analysis of X-ray measurements, this allowed for gaining novel insight into the thermodynamic properties of RX J1347.5-1145, as well as its formation history. The combination of SZ data with X-ray information is clearly central for obtaining a robust description of the intracluster gas and of any intracluster structures that attest to the dynamical nature of galaxy clusters. In particular, a joint SZ+X-ray high-resolution view of the shock fronts within galaxy clusters can help constraining a number of plasma properties fundamental to plasma physics on its own, as well as in the broader context of astrophysical processes, e.g., cluster and galaxy evolution, and the impact of merger and accretion processes of the cluster environment. Widely regarded as the "textbook example" of a cluster merger bow shock, the shock front in the "Bullet Cluster" (1E0657-56) represented the ideal test case for such an SZ study. The reconstruction of the shock properties specifically allowed for inferring the possible electron heating mechanisms taking place within the shocked gas. Finally, ALMA+ACA can serve as a powerful combination for providing direct and relatively inexpensive confirmation of galaxy clusters identified by other means (e.g., wide-field surveys at other wavelengths or with cosmic microwave background experiments) through the measure of their SZ signal. Although ALMA and ACA's mapping speeds are significantly lower than that of a SZ survey experiment, the angular resolution and sensitivity of ALMA+ACA allow one to easily measure the SZ effect from high-redshift systems. The study of a first pilot sample of galaxy cluster from the "Verification with the Atacama Compact Array - Localisation and Cluster Analysis" programme provided a first assessment of ACA's ability to get robust detections of high-redshift galaxy clusters and constraints on their masses.