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The Role of Quasars in the Formation of Massive Galaxies

  • Author(s): Vayner, Andrey
  • Advisor(s): Wright, Shelley A
  • et al.
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Abstract

This thesis studies actively accreting supermassive black holes (SMBH) known as quasars and their impact on the formation and evolution of massive galaxies. Theoretical work predicts that quasars are responsible for regulating the growth of the SMBH and its host galaxy. Winds driven by radiation pressure from the accretion disk and quasar jets are predicted to remove a substantial amount of gas from the host galaxy. Massive galaxies are observed to form the majority of their stars when the Universe was only 3.5 billion years old. During this epoch, the most massive SMBH already grew a substantial fraction of their mass. The SMBH is predicted to regulate the growth of the host galaxy during this co-evolutionary phase.

We have undertaken an extensive adaptive optics (AO) assisted integral field spectroscopy (IFS) survey of distant quasar host galaxies when the Universe was only 2.2-4.6 Gyr old. We conducted observations using the 10-meter W.M. Keck Observatory optical and infrared telescope. The survey aims to measure the gas-phase properties of quasar host galaxies such as metallicities, star formation rates, photoionization mechanisms, and search for galaxy-wide outflows potentially driven by the quasar. We detect outflows in all objects on scales from <1 kpc to 10 kpc. Half the outflows are consistent with being driven by a powerful energy-conserving shock, while the rest are either driven by radiation pressure or an isothermal shock. The outflows are the dominant source of gas depletion in these distant quasar host galaxies.

For the quasar 3C298, we have also conducted observations aimed at studying the molecular gas reservoir with the Atacama Large Millimeter Array (ALMA). In addition to detecting an ionized outflow in 3C298, we detect the first molecular outflow driven by a distant quasar. These observations show clear evidence for quasar driven outflows removing the molecular interstellar medium (ISM) through negative feedback.

The gas in the host galaxies is photoionized by a combination of O & B stars, the quasar, and radiative shocks. The chemical enrichment of the ISM is lower compared to the level observed in massive local galaxies. The quasar host galaxies appear to be under-massive relative to the mass of the SMBH based on local-scaling relations between the SMBH mass and galaxy mass. Substantial stellar growth and chemical enrichment are necessary if these galaxies are to grow and evolve into the most massive present-day elliptical galaxies.

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This item is under embargo until September 11, 2021.