Fredagskollokvium: The Physics behind Feedback from Quasars in Galaxy Evolution

Tiago Costa, Max Planck Institute for Astrophysics, Germany

Our leading model of galaxy formation hinges on strong energy injection by active

portrettbildet av en ung man
Dr. Tiago Costa, Max Planck Institute for Astrophysics. Photo: private.

galactic nuclei (AGN) powered by accreting supermassive black holes in order to explain the observed properties of galaxy populations. Even though "AGN feedback" is widely accepted as the chief source of energy operating in massive galaxies, the dominant physical mechanisms through which supermassive black holes supposedly shape galaxy evolution remain unidentified. This poor grasp of the physics underlying AGN feedback remains a major obstacle limiting

  1. a conclusive assessment of the role of AGN in galaxy evolution,
  2. the interpretation and constraining power of observational data,
  3. the development of realistic models for AGN feedback in state-of-the-art cosmological simulations.

In this talk, I will present results from numerical, (radiation-)hydrodynamic, cosmological simulations designed to test an array of specific AGN physical processes in massive galaxies at high-redshift (z > 2). These simulations make a strong case against "momentum-driven" feedback, ruling out direct radiation pressure from the AGN or large-scale outflows suffering strong cooling losses. The associated feedback is too weak, requiring unrealistically high black hole masses to effectively launch outflows. Our simulations single out two effective AGN feedback mechanisms. One is associated to radiation pressure arising from infrared photons trapped in dusty regions of the interstellar medium. This process has a strong impact on galactic nuclei, but can only operate effectively when AGN are highly obscured by dust. The most effective AGN feedback mechanism, I will argue, corresponds to "energy-driven" winds. Such outflows operate through hot, over-pressurised bubbles capable of ejecting gas from galaxies and of halting halo gas inflow through adiabatic expansion.

The talk will conclude with a discussion on the expected observational imprints of energy-driven bubbles, an analysis of their multi-phase structure as well as its origin, and an assessment of their impact on galaxy evolution.

gas, blue cloud, orange
In massive galaxies at high redshift (z > 2), large-scale cosmological inflows (blue) feed remarkably compact galaxies harbouring rapidly growing supermassive black holes in their nuclei. Energy released via radiation and winds by the associated active galactic nucleus (AGN) powers prodigious galactic superwinds (orange) capable of removing gas from the host galaxy (seen face-on in the inset plot) at rates of several thousands of solar masses per year. Outflows powered by AGN constitute a fundamental ingredient of galaxy evolution. Credits: Costa.

Please join via Zoom at

Meeting ID: 661 0643 6547
Passcode: 897682

Attendees will be muted during the colloquium, but will have the opportunity to ask questions at the end by clicking on the "raise hand” button.

Emneord: institute seminar, cosmology, fredagskollokvium, Kosmologi, Galaxy, AGN
Publisert 19. aug. 2021 17:00 - Sist endret 25. aug. 2021 13:45