Thesis

Birds of a feather: seeking the earliest high-energy events in the Universe at the high- and low-energy ends of the spectrum

• Call:

  PT-CERN Call 2020/2

• Academic Year:

  2020/2021

• Domain:

  Astroparticle Physics

• Supervisor:

  José Afonso

• Co-Supervisor:

• Institution:

  FCUL (Universidade de Lisboa)

• Host Institution:

  IA - Instituto de Astrofísica e Ciências do Espaço

• Abstract:

  The existence of powerful Active Galactic Nuclei (AGN) has now been established well within the first Gyr of the Universe, through the observations of tens of optically or near-infrared selected Quasi Stellar Objects (QSOs) up to the currently highest redshift of z ∼ 8. Theoretical work has been developed showing how super-massive (M∼ 109 M⊙) black holes can exist at such early epochs, depending on the unknown but necessarily quick assembly and growth from a suitable seed. To understand what are these supermassive black holes (SMBH) seeds, how they lead to early AGN activity and how relevant this is to the early galaxy and structure formation, it is fundamental to detect AGN activity at the highest redshifts, well within the Epoch of Reionisation. Surprisingly, the sensitivity already exists to find such sources at both extremes of the electromagnetic spectrum, X-rays and radio wavelengths, but all efforts to detect them have so far been unsuccessful. This is presumably due to their expected rareness, but certainly also due to the lack of understanding of the high-energy physical processes present in these youngest extreme sources in the Universe. While wide area surveys to be performed with future telescopes such as Athena (in the x-rays) and SKA (in the radio) will overcome the former limitation, the latter suggests correct identification of such ”rosetta stone” sources will remain challenging, as we are unable to optimise our observations and detection strategies to these sources. Taking advantage of the strong Portuguese participation in these two future international observatories, this PhD project will explore the synergies allowed by the combination of the unique capabilities of Athena and SKA for the exploitation of the earliest AGN activity. Following-up on our recent work (Amarantidis+2019), the student will explore state-of-the-art galaxy and SMBH formation and evolution models, analyse the physical processes they assume, and implement new recipes for X-ray and radio emission processes - taking into account the most recent advances in our understanding of black hole accretion physics. This will lead to improved methodologies for the selection of very high redshift AGN, which will be tested in current deep X-ray and radio surveys. Finally, such methodologies will be used to optimise Athena and SKA observing strategies for the detection of the earliest examples of AGN activity.