Probing the Evolution of Dusty Star-Forming Galaxies at the Cosmic Noon via Strong Gravitational Lensing

The primary objective of this thesis is to explore the early stages of the evolution of Dusty Star-Forming Galaxies (DSFGs) by leveraging the physical phenomenon of strong gravitational lensing. This population of galaxies represents the ideal testing laboratories for galaxy evolution studies, as they constitute the bulk population at the peak of Cosmic Star Formation History and they have been identified as the progenitors of massive quiescent early-type galaxies. The magnification effect induced by a foreground lens, such as a low-redshift massive elliptical galaxy, offers a unique opportunity to investigate the intricate morphology of distant and compact galaxies such as DSFGs, overcoming the resolution and sensitivity limits imposed by the current instrumentation. Strong lensing therefore enables us to gain unprecedented insights into the processes that guided the evolution of star-forming progenitors toward becoming the massive elliptical galaxies we observe today. To achieve this objective, this work aims to explore the in-situ scenario for galaxy-black hole co-evolution by testing its predictive capabilities to self-consistently interpret the outcomes obtained from observational analyses. In my research, I employed a composite approach, combining the exploration of empirical relationships within samples of strongly lensed DSFGs with a detailed investigation into the morphological and physical characteristics of individual objects. Both methodologies benefit from the advantages offered by gravitational lensing. The former allows the study of fainter luminosity regimes, while the latter provides access to intricate structures of distant and compact objects like DSFGs. The investigation began with a sample of sub-millimeter-selected (candidate) strongly lensed DSFGs identified within the Herschel-ATLAS survey. The sample was originally selected based on a straightforward flux density threshold of S_500 μm > 100 mJy, resulting in redshifts spanning 1 ≲ z ≲ 4.5 and apparent Infrared (IR) luminosities in the range of 10^13≲ LIR /L⊙ ≲ 10^14. These properties make this sample an ideal testing ground for investigating the evolution of DSFGs during the cosmic noon and the interplay between black holes and their host galaxies. This work also emphasises the significance of multi-wavelength broad-band and spectroscopic observations in studying the evolution of massive star-forming progenitors of early-type galaxies, spanning from the UV/optical to the radio regime. To achieve this, I integrated data available in the literature, public surveys or telescopes, and high-quality archival and proprietary data. This included data from telescopes such as HST in the optical/NIR, the Spitzer and Herschel space observatories in the MIR-to-FIR range, interferometric ALMA (sub-)millimetric continuum and spectroscopic observations, and proprietary radio data from the ATCA telescope. My work complemented these high-quality multi-wavelength observations with modern analysis techniques, including lens modelling and source reconstruction methods, to reveal the unlensed structure of DSFGs down to sub-kpc scales, and Spectral Energy Distribution fitting to access the integrated physical properties of these objects. In this work, I investigated the interplay between galaxy formation and nuclear activity by examining the Far-Infrared/Radio correlation (FIRRC) of a sample of (candidate) strongly lensed DSFGs with radio counterparts. Gravitational lensing allowed for the observation of such a relation over a wide range of redshifts and luminosities. Our resulting trend of the FIRRC indicates a transition from an earlier phase of dust-obscured star formation to a later, radio-loud quasar phase. Simultaneously, the strong lensing effect enabled a detailed analysis of the reconstructed source-plane morphology and sizes, the ISM content (dust and gas), and integrated properties (luminosities, masses, ages, and kinematics) of an individual strongly lensed DSFG at z∼3. These results precisely pinpointed the evolutionary phase of the galaxy in accordance with the predictions yielded by the in-situ scenario. In conclusion, this research contributes significantly to our understanding of DSFGs by exploiting the gravitational lensing effect to investigate their evolution, morphology, and physical properties. It also highlights the importance of empirical relationships among samples and the detailed examination of individual objects as a multi-faceted approach to deepen our comprehension of galaxy evolution during the peak of the Cosmic Star Formation History.