Within the field of astronomy, understanding how galaxies grow and evolve from the Big Bang to the present day is a challenging and complex question. Radio observations - unhindered by dust... Show moreWithin the field of astronomy, understanding how galaxies grow and evolve from the Big Bang to the present day is a challenging and complex question. Radio observations - unhindered by dust attenuation - are a powerful tool in studying the formation of stars and subsequent buildup of galaxies. In this thesis, the distant star formation is studied using radio observations from the VLA COSMOS-XS survey specifically. In Chapter 2, we discuss the details of the sensitive COSMOS-XS survey and present the derived Euclidean-normalized source counts. In Chapter 3, we derive the dust-unbiased star formation rate density out to high redshift and present evidence for a significant underestimation of the star formation rate density based on ultraviolet observations. In Chapter 4, the focus shifts to the ‘optically dark’ population: extremely dust-obscured sources that are invisible even in deep ultraviolet imaging. We identify these sources with the COSMOS-XS survey and use them to quantify their contribution to the total star formation rate density. In Chapter 5, we present new ALMA observations of ‘optically dark’ sources and confirm the cosmic importance of ‘optically dark’ sources at high redshift. Show less
One of the key quests in astronomy is to study the growth and evolution of galaxies across cosmic time. Radio observations provide a powerful means of studying the formation of stars and subsequent... Show moreOne of the key quests in astronomy is to study the growth and evolution of galaxies across cosmic time. Radio observations provide a powerful means of studying the formation of stars and subsequent buildup of distant galaxies, in a way that is unbiased by the presence of dust. This thesis provides a detailed view of faint, star-forming galaxies in the early Universe through sensitive radio observations, and compiles several studies probing distant star formation with both radio synchrotron and free-free emission. In Chapter 2, we detect a large number of galaxies using sensitive new radio data from the Very Large Array, allowing us to separate radio emission from star formation and active galactic nuclei in the faint radio sky. In Chapter 3, we calibrate synchrotron emission as a tracer of star formation in distant starburst galaxies, while in Chapters 4 & 5 we turn towards radio free-free emission — a faint but very powerful tracer of star formation. Using sensitive new radio data at high frequencies, we perform the first detailed studies of free-free emission in distant galaxies. Show less
This thesis explores the theoretical and observational properties of distant massive galaxies that harbour active black holes in their centres and shine brightly at radio wavelengths. These radio... Show moreThis thesis explores the theoretical and observational properties of distant massive galaxies that harbour active black holes in their centres and shine brightly at radio wavelengths. These radio galaxies are some of the rarest objects in the Universe, and studying them reveals more about the formation and evolution of massive galaxies and black holes in the Universe. In Chapter 2, we model faint radio galaxies at record distances (high redshifts) using a simple model to characterise the overall evolution of radio galaxies. We find that our model replicates well the properties of radio galaxies that are nearer to us. This gives us confidence in the predictions at higher redshifts (larger distances), where data is scarce. In Chapter 3, we compile a list of promising distant radio galaxies using all-sky radio datasets. We present observations for these candidates at a high resolution. In Chapter 4, we report the discovery of the most distant radio galaxy observed till date, TGSS J1530+1049. The galaxy’s distance is confirmed using data from various telescopes. In Chapter 5, we present a detailed study of other distant radio galaxies from our initial sample, showing their properties to be different from brighter radio galaxies. Show less
