The chapter discusses the observational evidence for Active Galactic Nucleus (AGN) feedback, which occurs when the energy and radiation generated by the accretion of matter onto a supermassive black hole in the center of a galaxy interact with the surrounding interstellar medium. This interaction can lead to the ejection or heating of gas, potentially terminating star formation and reducing the rate of black hole accretion. The feedback can be categorized into two main modes: the radiative or wind mode, and the kinetic or radio mode.
1. **Radiative or Wind Mode**: This mode operates when the AGN is highly luminous, often at or near the Eddington limit. It involves the interaction of quasar radiation with dust and gas, pushing cold gas out of the galaxy. The radiative pressure from the quasar can prevent the galaxy from accreting matter at its maximum rate, leading to a correlation between the black hole mass and the stellar velocity dispersion of the galaxy. Observational evidence for this mode includes the presence of AGN winds and outflows, which can be observed through absorption lines in quasar spectra and the velocity fields of galactic outflows.
2. **Kinetic or Radio Mode**: This mode is more common in massive elliptical galaxies and involves the mechanical energy of radio-emitting jets. These jets heat the hot intracluster medium, reducing radiative cooling and subsequent star formation. The energy flow is roughly continuous, maintaining a long-lived heating/cooling balance. Observational evidence for this mode includes the detection of bubbles in the hot gas surrounding galaxies in cool core clusters, which are powered by the jets from the central AGN.
The chapter also discusses the implications of AGN feedback for galaxy evolution, including the cosmic downsizing of AGN, where the most luminous and massive AGN were most numerous at high redshifts, and the secular evolution of galaxies over time. The feedback process is thought to play a crucial role in shaping the properties of galaxies, such as their bulge mass and stellar velocity dispersion.
Finally, the chapter highlights the importance of future observational studies using advanced telescopes and instruments to better understand the various modes of AGN feedback and their impact on galaxy evolution.The chapter discusses the observational evidence for Active Galactic Nucleus (AGN) feedback, which occurs when the energy and radiation generated by the accretion of matter onto a supermassive black hole in the center of a galaxy interact with the surrounding interstellar medium. This interaction can lead to the ejection or heating of gas, potentially terminating star formation and reducing the rate of black hole accretion. The feedback can be categorized into two main modes: the radiative or wind mode, and the kinetic or radio mode.
1. **Radiative or Wind Mode**: This mode operates when the AGN is highly luminous, often at or near the Eddington limit. It involves the interaction of quasar radiation with dust and gas, pushing cold gas out of the galaxy. The radiative pressure from the quasar can prevent the galaxy from accreting matter at its maximum rate, leading to a correlation between the black hole mass and the stellar velocity dispersion of the galaxy. Observational evidence for this mode includes the presence of AGN winds and outflows, which can be observed through absorption lines in quasar spectra and the velocity fields of galactic outflows.
2. **Kinetic or Radio Mode**: This mode is more common in massive elliptical galaxies and involves the mechanical energy of radio-emitting jets. These jets heat the hot intracluster medium, reducing radiative cooling and subsequent star formation. The energy flow is roughly continuous, maintaining a long-lived heating/cooling balance. Observational evidence for this mode includes the detection of bubbles in the hot gas surrounding galaxies in cool core clusters, which are powered by the jets from the central AGN.
The chapter also discusses the implications of AGN feedback for galaxy evolution, including the cosmic downsizing of AGN, where the most luminous and massive AGN were most numerous at high redshifts, and the secular evolution of galaxies over time. The feedback process is thought to play a crucial role in shaping the properties of galaxies, such as their bulge mass and stellar velocity dispersion.
Finally, the chapter highlights the importance of future observational studies using advanced telescopes and instruments to better understand the various modes of AGN feedback and their impact on galaxy evolution.