The origin and evolution of galaxies are closely linked to many different physical phenomena. Among them, the most important one is the environment they reside in. Isolated and cluster member... Show moreThe origin and evolution of galaxies are closely linked to many different physical phenomena. Among them, the most important one is the environment they reside in. Isolated and cluster member galaxies indeed are affected by different forces which affect their evolution. The main concern of this thesis is to understand such forces and how they are related to galaxy evolution. Therefore, this thesis covers various topics including black hole mass calculations, the black hole mass-stellar velocity dispersion relation, the nature of AGN emission in galaxy clusters and field galaxies, a detailed investigation of X-ray and optical galaxy overdensity phenomenon, and the dynamical processes in pre-merging galaxy clusters. Show less
In this thesis, the research focuses on the properties of dark matter and dark matter haloes and how they connect with the galaxies we can observe in the Universe. Because of the still unknown... Show moreIn this thesis, the research focuses on the properties of dark matter and dark matter haloes and how they connect with the galaxies we can observe in the Universe. Because of the still unknown nature of dark matter, we tend to study it using the properties of its distribution and its properties on galactic scales and beyond. The galaxy–dark matter connection is important for three main reasons, and understanding it helps with answering the largest questions in astrophysics and cosmology today. First question includes the understanding of the physics of galaxy formation. Secondly, the inference of cosmological parameters – if we want to robustly measure the cosmological parameters, we have to understand, how the galaxies interplay with the dark matter, and thirdly, the inference of evolution of matter distribution and properties of dark matter. We explore different aspects of the galaxy–dark matter connection that can be measured using gravitational lensing, more specifically, using galaxy-galaxy lensing as our primary probe. We use the halo model together with the halo occupation distributions to statistically describe the galaxy-halo connection and to constrain assembly bias in rich galaxy groups. The same theoretical framework is also used to constrain the nature of galaxy bias. Show less
In this thesis, we use low-frequency and high-frequency radio observations to address the following questions regarding quasars: is the radio loud/quiet quasar dichotomy real?; can deep low... Show moreIn this thesis, we use low-frequency and high-frequency radio observations to address the following questions regarding quasars: is the radio loud/quiet quasar dichotomy real?; can deep low-frequency radio observations be used to effectively select high-z quasars?; how does the faint radio-selected quasar population evolve with redshift?; is the environment of quasars related to the origin of their radio-emission. For this purpose, we use low-frequency and high-frequency radio imaging, spectroscopic quasar catalogs, and ancillary optical and infrared data. The second chapter of the thesis uses existing radio and spectroscopic catalogs of quasars to study the clustering properties of RQQs and RLQs. The third chapter uses a directional-dependent calibration algorithm known as facet-calibration to obtain a deep LOFAR 150 MHz mosaic of the NOAO Deep Wide-Field Survey Boötes field. The remaining chapters combine the catalog obtained from the deep LOFAR mosaic presented with ancillary optical/infrared data to study the selection of high-z quasars using LOFAR observations, and to investigate the evolution of radio-selected quasars with redshift. 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
This thesis presents pioneering work on the panchromatic emission of some of the most luminous galaxies in the early Universe: star forming galaxies and active galactic nuclei. Using state-of... Show moreThis thesis presents pioneering work on the panchromatic emission of some of the most luminous galaxies in the early Universe: star forming galaxies and active galactic nuclei. Using state-of-the-art statistical methods and new-generation radio-to-X-rays instruments, this thesis expands the parameter space covered by current multi-wavelength studies of galaxy evolution. In particular, this thesis pushes three different frontiers. The statistical frontier is explored by developing a sophisticated statistical tool to robustly recover the parameters required to model multi-wavelength emission. The wavelength frontier is pushed forward by exploring galaxy evolution from the new spectral window at low-frequency radio, opened by the LOFAR instrument. Finally, the resolution frontier will be pushed by exploring the distribution of emission components across the spectrum using a combination of high-resolution ALMA and HST imaging. Show less
Whereas the extreme conditions of the first minutes after the Big Bang have produced nearly all the hydrogen and helium in the Universe, heavier elements - or metals - are synthesised in the... Show moreWhereas the extreme conditions of the first minutes after the Big Bang have produced nearly all the hydrogen and helium in the Universe, heavier elements - or metals - are synthesised in the core of stars and in supernova explosions. Currently, however, the behaviour of supernovae (and their stellar progenitors) is not well understood, and could be better constrained by measuring accurately the relative amount of metals they produce. On the other hand, the very hot and diffuse gas - or intra-cluster medium (ICM), glowing in X-ray and detected in the large gravitational potential well of galaxy clusters and groups, is also rich in metals. This means that the building blocks of life, synthesised by billions of supernovae over cosmic times, are present even at the largest scales of the Universe, as they enrich the ICM. In this thesis, I show how measuring the abundances of O, Ne, Mg, Si, S, Ar, Ca, Cr, Mn, Fe, and Ni in a sample of nearby, relaxed galaxy clusters, groups, and ellipticals observed with XMM-Newton (the CHEmical Enrichment Rgs Sample) helps to better understand Type Ia and core-collapse supernovae, as well as the history and conditions of the ICM enrichment in general. Show less
This thesis uses novel observations from the Low Frequency Array to address open questions on the topic of galaxy evolution. The highest resolution images at ultra low radio frequencies are used to... Show moreThis thesis uses novel observations from the Low Frequency Array to address open questions on the topic of galaxy evolution. The highest resolution images at ultra low radio frequencies are used to investigate the physical processes present in the radio emission from distant galaxies. Detections of spectral features from carbon atoms in a nearby galaxy are also presented and used to constrain the temperature and density of cold gas that is a key component of all galaxies. Show less
Radio observations provide a unique view of black holes in the Universe. This thesis presents low frequency radio images and uses the radio sources in those images to study the evolution of black... Show moreRadio observations provide a unique view of black holes in the Universe. This thesis presents low frequency radio images and uses the radio sources in those images to study the evolution of black holes and galaxies through the age of the Universe. Show less
In this thesis the molecular emission of species such as CO, HCN and HNC and HCO+ are used to probe and quantify mechanical heating in star-forming galaxies. In the first part of the thesis photo... Show moreIn this thesis the molecular emission of species such as CO, HCN and HNC and HCO+ are used to probe and quantify mechanical heating in star-forming galaxies. In the first part of the thesis photo-dissociation models are used to find a diagnostic of mechanical heating at the level of molecular clouds. It was shown that mechanical heating leaves a strong signature in diagnostics that involve high-J to low-J transitions. In the second part of the thesis , synthetic line emission maps of molecular species are computed for model star-forming galaxies. The emission from these maps are used as input to photo-dissociation models in-order to constrain the physical properties, such as gas density and visual extinction, of star-forming galaxies. It was demonstrated that it is essential to consider mechanical heating in modelling the emission of star-forming galaxies using photo-dominated models. Show less
Over the past 15 years, the field of extragalactic astronomy has pushed to high redshift and our knowledge of natal galaxies has grown dramatically. Galaxies are now routinely detected at redshifts... Show moreOver the past 15 years, the field of extragalactic astronomy has pushed to high redshift and our knowledge of natal galaxies has grown dramatically. Galaxies are now routinely detected at redshifts z ! 6__7 (e.g. Bouwens et al. 2010; Labb_e et al. 2010; Oesch et al. 2010; Bouwens et al. 2011; McLure et al. 2011). However, there are fundamental concepts that are still poorly understood. How do galaxies get their gas? How does galactic feedback affect galaxy evolution? Show less
