Active Galactic Nuclei (AGN) feedback mechanisms are processes where energy released by supermassive black holes—through intense radiation or mechanical jets—heats or expels surrounding gas, regulating star formation and galaxy growth. It acts as a “thermostat,” preventing galaxies from becoming too massive and defining the co-evolution of galaxies and their central black holes. [1, 2, 3, 4]

Key AGN Feedback Mechanisms

• Quasar Mode (Radiative/Wind Mode): Occurs during high-rate accretion (near Eddington limit) when the AGN is young or active. Intense radiation pressure drives fast, wide-angle winds, removing cold gas and curbing star formation.
• Radio Mode (Mechanical/Jet Mode): Occurs at lower accretion rates, common in massive, mature elliptical galaxies. Relativistic jets push against the intracluster medium, forming bubbles and injecting heat that prevents surrounding gas from cooling, thus starving the galaxy of star-forming material.
• Positive Feedback: Instead of suppression, some jets or outflows compress cold gas clouds in the interstellar medium (ISM), potentially triggering star formation rather than halting it. [1, 2, 3, 4, 5]

Components and Effects

• Energy Injection: AGN inject energy and momentum directly into the ISM and circumgalactic medium (CGM), preventing gas cooling.
• Gas Outflows: Powerful outflows, sometimes called “ultrafast outflows” (UFOs), act to clear out the host galaxy.
• Morphological Impact: These mechanisms are crucial for reproducing the observed luminosity function of galaxies, acting as a key component of the. [1, 2, 3, 4, 5]

Contextual Role
These feedback loops are essential in cosmological simulations (e.g.,) to prevent galaxies from becoming too bright and massive, resolving the discrepancies between theoretical models and observations. [1, 2, 3]

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