High-redshift active galactic nuclei and their environment
Doctoral thesis, 2020

In order to understand the formation and evolution of local massive galaxies and to reveal the processes that engineered the tight correlations found between their supermassive black hole (SMBH) mass and bulge mass or velocity dispersion, the study of powerful, high-redshift active galactic nuclei (AGNs) and their environment is crucial. AGNs are luminous targets providing important clues to galaxy evolution, as their central SMBH is growing at high rates, which opens the opportunity to unfold how the growth of the black hole influences the growth of its host galaxy. Moreover, powerful high-z AGNs are hosted by massive galaxies and likely trace protoclusters, where the progenitors of present-day massive galaxies reside. Observations of high-z quasars and radio galaxies suggest that these AGNs live in overdense environment surrounded by star-forming Lyman-alpha emitters and submillimetre galaxies. At smaller scales several high-z quasars and radio galaxies have gas-rich and/or star-forming companion galaxies.

The aim of this thesis is to study the environment of high-z quasars and radio galaxies through submillimetre and CO spectral line observations and to contribute to the effort of uncovering the underlying processes that shape the evolution of massive galaxies. The thesis focuses on three case studies of high-z AGN-companion galaxy systems at z=2-3. These were selected based on the AGN host galaxy appearing as gas-poor, while the companion galaxy being very gas-rich. However, sensitive observations with the Atacama Large Millimeter/submillimeter Array and the Karl G. Jansky Very Large Array, tracing CO line emission and dust continuum emission, revealed that a significant amount of molecular gas and dust emission is associated with the host galaxies of the AGNs. My results highlight the importance of sensitive and high-resolution observations and demonstrate that high-z AGN systems are more complex and diverse, than it is implied by theoretical studies.

galaxies: evolution -- galaxies: high-redshift -- galaxies: active -- galaxies: Starburst -- -- Submillimeter: galaxies

Opponent: Dr. Alexandra Pope, Department of Astronomy, University of Massachusetts, USA

Author

Judit Fogasy

Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics, Extragalactic Astrophysics

SMM J04135+10277: a distant QSO-starburst system caught by ALMA

Monthly Notices of the Royal Astronomical Society,; Vol. 493(2020)p. 3744-3756

Journal article

Judit Fogasy, K. K. Knudsen, G. Drouart and B. Gullberg: ALMA detects molecular gas in the halo of the powerful radio galaxy TXS 0828+193

J. Fogasy, K. K. Knudsen and E. Varenius: VLA detects CO(1-0) emission in the z = 3.65 quasar SDSS

The Universe contains billions of galaxies, which come in may different sizes and colours. The main building blocks of these galaxies are stars, a central supermassive black hole (SMBH), dark matter and the interstellar medium. At present-day there are two main types of galaxies: spiral galaxies, which have both young and old stars and massive ellipticals, which have mainly old stars. In addition, observations of elliptical galaxies and the bulges of spiral galaxies revealed tight correlations between some properties of the host galaxy and the mass of its SMBH, which suggest co-evolution of the galaxies with their SMBHs.

In order to understand how galaxies formed and evolved into different types, and to reveal the processes that shaped their evolution, we need to look back in time to find their progenitors. Active galactic nuclei (AGNs) at cosmological distances are the prefect targets for this, as these are bright sources, where the central SMBH is actively growing. Moreover, such distant, powerful AGNs are hosted by massive galaxies and likely trace over-dense environments or protoclusters. 

The aim of this thesis is to study the environment of cosmologically distant quasars and radio galaxies, the possible progenitors of local massive galaxies. The thesis presents three case studies of AGN-companion galaxy systems found at 1.7-2.5 billion years after the Big Bang, and which were selected based on the AGN host galaxy appearing gas-poor, while the companion galaxy being very gas-rich. 

Much our previous knowledge of the gas and dust in distant AGNs and their host galaxies has been derived from low-resolution observations making it difficult to disentangle the contribution from companion galaxies. In my thesis we have challenged previous results using higher quality data at mm and radio wavelengths.These observations revealed that a significant amount of molecular gas and dust emission is associated with the host galaxies of the AGNs. My results highlight the importance of sensitive and high-resolution observations and demonstrate that high-z AGN systems are more complex and diverse, than it is implied by theoretical studies.

Subject Categories

Astronomy, Astrophysics and Cosmology

Roots

Basic sciences

ISBN

978-91-7905-326-0

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 4793

Publisher

Chalmers University of Technology

Online

Opponent: Dr. Alexandra Pope, Department of Astronomy, University of Massachusetts, USA

More information

Latest update

5/28/2020