Finding the first quasars at birth

Abstract

Recent discoveries confirming the existence of supermassive black holes, with masses in excess of a billion solar masses, forming less than a billion years after the Big Bang poses a major challenge to our understanding of the formation of the first galaxies and black holes in the universe.

Amongst the main candidate theories for the formation of supermassive black hole seeds, it remains unclear whether stellar mass primordial star black hole seeds or seeds formed in dense stellar clusters would have encountered sufficient gas reservoirs in their host environments to grow rapidly, and it is expected that they would struggle to reach the required mass in the available time, even under conditions of persistent Eddington growth.

In this thesis we will focus our attention on the promising direct collapse black hole scenario in which a monolithic collapse occurs in a hot atomically cooled primordial halo exposed to a sufficiently strong Lyman-Werner flux from a nearby star forming halo. A supermassive primordial star forms at the centre of the halo which grows under accretion rates of up 1 M_⊙ yr⁻¹ and reaches a mass of up to a few 10⁵ M_⊙, before collapsing directly to a black hole.
We present realistic synthetic spectra of supermassive stars in their birth envelopes calculated using the spectral synthesis code Cloudy, with data extracted from cosmological simulations in which they were modelled using the radiation hydrodynamics code Enzo. Spectra are calculated for two types of supermassive star predicted by stellar evolution models: cool, red hypergiants at 6000-8000 K with luminosities greater than 10¹⁰ L_⊙ and hot, blue stars with with surface temperatures of 20,000 - 40,000 K. We also calculate spectra for a direct collapse black hole at birth in its host environment that was born in cold accretion flows in which it is destined to grow to 10⁹ M_⊙ by z ∼ 7, again modelled using Enzo. We calculate near infrared AB magnitudes for these objects at source redshifts ranging from z = 20 down to 6 for various telescopes to be launched in the next decade, and determine out to which redshifts they are observable in the near infrared today given the instrumental detection limits.

Date of Award	Jul 2020
Original language	English
Awarding Institution	University of Portsmouth
Supervisor	Andrew Lundgren (Supervisor) & Daniel Whalen (Supervisor)