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Exploring Radio WISE Selected Galaxies: An investigation into the properties of the most extreme galaxies in the universe.

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posted on 22.09.2022, 09:01 authored by Emily R. Ferris

This thesis presents analysis of ISAAC photometric and X-shooter spectroscopic observations of 30 selected high redshift galaxies at z = 0.880 - 2.853. Uncovered through cross matching sources from the WISE All-Sky catalogue with the NVSS radio source catalogue, Radio selected WISE Galaxies (RWGs) are extremely luminous with bolometric luminosities exceeding 1013 L⊙. With expected reddening of E(B-V) > 0.9 magnitudes, this dusty and obscured population of new and unique radio intermediate galaxies are critical to our understanding of the properties and evolution of high redshift, ultra luminous IR galaxies. Theorised to be a new stage galaxy evolution, RWGs represent a super active BH growth and feedback phase, which all AGN may experience, therefore allowing us to observe these sources and their environments the most extreme state, increasing our knowledge of this peak phase in galaxy and quasar evolution. 

I first measure the J and Ks band flux densities of 30 RWGs and use the MAGPHYS code to fit their SEDs, aiming to understand the size of the sources. I then present detections and spectral fitting of four broad multi-component emission lines (Hα, Hβ, [Oiii]λ5007 and Civ) across 18 RWGs, with three independent methods used to determine black hole and host galaxy masses. Following on, I discuss the assumptions made when calculating my black hole masses, aiming to quantify the expected super Eddington ratios of RWGs and the effect that high visual extinctions have on these measured masses, in order to fully understand how extreme and unique these sources are. Finally, I make use of the full 300 - 2480nm wavelength range of X-shooter’s three spectroscopic arms and fit multi Gaussian models to a total of 100 individual line profiles across 15 line variants and 23 RWGs. I use these measured emission and absorption line properties to investigate the characteristics of the line profiles in order to compare RWGs to a standard quasar population. Throughout this investigation I also find that RWGs remain a distinct population from similarly detected HotDOGs and are ∼ 1 dex smaller in mass and therefore likely a shorter evolutionary phase. Finally, I aim to uncover the driving mechanisms behind these unique radio galaxies by placing them on BPT diagrams and find a new selection criteria that can be used to help determine future RWGs.

History

Supervisor(s)

Andrew Blain; Michael Watson

Date of award

10/06/2022

Author affiliation

School of Physics and Astronomy

Awarding institution

University of Leicester

Qualification level

Doctoral

Qualification name

PhD

Language

en