8.4 Feedback Mechanisms and Galaxy Co-evolution
3 min read•august 9, 2024
(AGN) wield immense power over their host galaxies. Through radiative and , they shape galactic evolution, regulating star formation and . This dynamic interplay between AGN and their surroundings is crucial for understanding galaxy formation.
mechanisms create a delicate balance in galactic ecosystems. By heating gas, driving , and altering the , AGN influence star formation rates and galaxy growth. This feedback loop connects the growth of supermassive black holes to their host galaxies' evolution.
AGN Feedback Mechanisms
Types of AGN Feedback
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Top images from around the web for Types of AGN Feedback
Frontiers | Probing the Gas Fueling and Outflows in Nearby AGN with ALMA View original
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Frontiers | The Many Routes to AGN Feedback View original
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Frontiers | Probing the Gas Fueling and Outflows in Nearby AGN with ALMA View original
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- AGN feedback describes how active galactic nuclei influence their host galaxies and surrounding environments
- occurs when intense radiation from AGN heats and ionizes surrounding gas
- Prevents gas from cooling and forming new stars
- Can drive gas outflows through
- Mechanical feedback involves physical ejection of material from the AGN
- Jets of relativistic particles push gas out of galactic centers
- Creates cavities in surrounding hot gas
- Outflows from AGN expel gas from galaxies at high velocities
- Can reach speeds of 1000 km/s or more
- Remove potential fuel for star formation
Mechanisms of AGN Feedback
- Radiation pressure exerts force on dust grains in surrounding gas
- Accelerates gas outward from the AGN
- Can clear central regions of galaxies
- raises temperature of gas near AGN
- Makes gas too hot to collapse and form stars
- Creates a zone of inhibited star formation
- by AGN radiation changes the ionization state of gas
- Alters cooling rates and chemistry of interstellar medium
- Can suppress star formation in affected regions
Effects on Galactic Environment
- AGN feedback creates bubbles and cavities in hot gas around galaxies
- Visible in X-ray observations of
- Prevent from depositing gas in galactic centers
- Feedback regulates growth of both the AGN and host galaxy
- Establishes a balance between accretion and outflows
- Leads to observed correlations between black hole and galaxy properties
- Impacts extend beyond host galaxy to intergalactic medium
- Can heat and enrich intergalactic gas with metals
- Influences evolution of galaxy groups and clusters
Impact on Galaxy Evolution
Quenching of Star Formation
- Star formation quenching occurs when AGN feedback halts or reduces star formation in galaxies
- Removes or heats gas needed for new star formation
- Can rapidly transition galaxies from star-forming to quiescent states
- AGN outflows expel large amounts of gas from galaxies
- Reduces fuel available for future star formation
- Can lead to long-term suppression of star formation
- Heating of galactic gas prevents it from cooling and collapsing to form stars
- Maintains gas in a hot, diffuse state
- Creates a stable configuration that inhibits new star formation
Co-evolution of Black Holes and Galaxies
- describes the linked growth of supermassive black holes and their host galaxies
- Observed in tight correlations between black hole mass and galaxy properties (bulge mass, velocity dispersion)
- Suggests a feedback mechanism regulating growth of both components
- AGN activity can trigger in some cases
- Compression of gas by AGN outflows can initiate intense star formation
- Often followed by a quenching phase as gas is depleted or expelled
- between galaxies can fuel both AGN activity and star formation
- Provides gas to feed central black hole and form new stars
- AGN feedback eventually terminates this phase of rapid growth
Regulation of Gas Flows
- Cooling flows in galaxy clusters deposit cool gas onto central galaxies
- Can fuel star formation and black hole growth in cluster centers
- AGN feedback disrupts these flows, preventing runaway growth
- balances radiative cooling in many galaxies and clusters
- Creates a stable equilibrium preventing overcooling of gas
- Maintains galaxies in a relatively quiescent state
- Feedback influences the gas content and distribution in galaxies over time
- Shapes the observed properties of galaxies across cosmic history
- Helps explain the observed (star-forming vs quiescent)
Key Terms to Review (20)
Active Galactic Nuclei: Active Galactic Nuclei (AGN) are extremely bright regions at the centers of some galaxies, powered by supermassive black holes that accrete matter at an incredible rate. The intense energy output from these regions is due to various processes, including the gravitational energy released as matter falls into the black hole, making AGN key players in understanding galaxy formation and evolution.
AGN Feedback: AGN feedback refers to the energetic influence of active galactic nuclei (AGNs) on their host galaxies, which can regulate star formation and affect the overall evolution of galaxies. This process involves the release of energy and momentum from accreting supermassive black holes at the centers of galaxies, shaping their environment through various feedback mechanisms. It plays a critical role in understanding how galaxies co-evolve with their central black holes and the surrounding interstellar medium.
Agn heating: AGN heating refers to the process by which Active Galactic Nuclei (AGNs) release immense amounts of energy, impacting their surrounding environments, particularly in galaxies. This energy is produced as matter falls into supermassive black holes, resulting in the emission of radiation across various wavelengths. AGN heating plays a crucial role in regulating star formation and influencing the evolution of galaxies over cosmic time.
Bimodality in galaxy populations: Bimodality in galaxy populations refers to the existence of two distinct groups of galaxies, typically separated by their properties such as color, morphology, and star formation rates. This concept highlights the dichotomy between early-type galaxies, which are generally red, elliptical, and passively evolving, and late-type galaxies, which are blue, spiral, and actively forming stars. Understanding this bimodal distribution is essential for studying how galaxies evolve over time and how they interact with their environments.
Black hole-galaxy co-evolution: Black hole-galaxy co-evolution refers to the interconnected growth and development of supermassive black holes and their host galaxies over cosmic time. This relationship implies that the formation and evolution of galaxies are influenced by the presence and activity of black holes, while black holes themselves are shaped by the characteristics and dynamics of their surrounding galaxies. These interactions highlight how feedback mechanisms, such as energy output from black hole accretion and galactic winds, play a critical role in regulating star formation and galaxy morphology.
Co-evolution of black holes and galaxies: The co-evolution of black holes and galaxies refers to the interconnected growth and development of supermassive black holes at the centers of galaxies alongside the evolution of their host galaxies. This relationship suggests that the formation and growth of galaxies are significantly influenced by the processes occurring in their central black holes, leading to a feedback loop where each affects the other over cosmic timescales.
Compton Heating: Compton heating refers to the process by which high-energy photons, such as X-rays or gamma rays, collide with electrons, resulting in the transfer of energy from the photons to the electrons. This energy transfer can increase the temperature of the gas in which these interactions occur, playing a crucial role in the thermal dynamics of various astrophysical environments, especially in feedback mechanisms that influence galaxy evolution.
Cooling Flows: Cooling flows refer to the process in which hot gas in galaxy clusters loses energy and cools down, leading to a flow of cooler gas towards the center of the cluster. This phenomenon is essential in understanding how galaxies evolve, as the cooling gas can fuel star formation and affect the dynamics of the cluster. The interaction between cooling flows and feedback mechanisms also plays a critical role in the co-evolution of galaxies and their surrounding environments.
Galactic environment: The galactic environment refers to the surrounding conditions and characteristics of a galaxy that influence its formation, evolution, and overall behavior. This includes the distribution of gas, dust, dark matter, and the presence of neighboring galaxies, all of which play crucial roles in shaping the processes within a galaxy. Understanding the galactic environment is essential for grasping how galaxies interact with their surroundings and how feedback mechanisms contribute to galaxy co-evolution.
Galaxy clusters: Galaxy clusters are large groups of galaxies held together by gravity, consisting of hundreds to thousands of individual galaxies, along with dark matter and hot gas. These clusters serve as important laboratories for studying galaxy formation and evolution, revealing the effects of feedback mechanisms on their development, the role they play in large-scale structure formation, and how they fit into the cosmic web.
Gas flows: Gas flows refer to the movement of gas, often in the form of hydrogen, helium, or other elements, through various regions of space and within galaxies. This movement is essential for understanding how galaxies evolve over time as it influences star formation, chemical enrichment, and the dynamics of galaxy interactions. Gas flows can be driven by gravitational forces, radiation pressure, or supernova feedback, leading to complex feedback mechanisms that play a critical role in galaxy co-evolution.
Interstellar Medium: The interstellar medium (ISM) is the matter that exists in the space between stars in a galaxy, consisting of gas, dust, and cosmic rays. This material plays a crucial role in the formation and evolution of stars and galaxies, acting as both a reservoir for star formation and a medium through which energy and matter are exchanged. The ISM is influenced by galactic magnetic fields and has significant interactions with cosmic rays, impacting the overall dynamics and chemistry of the galaxy.
Mechanical feedback: Mechanical feedback refers to the process by which physical forces or motions in a system lead to changes in that system's behavior or state. In astrophysical contexts, this feedback can influence star formation and galaxy evolution by regulating the energy and material outflows from stars, which in turn affect the surrounding interstellar medium and future star formation activity.
Mergers: Mergers refer to the process where two or more galaxies combine to form a single, larger galaxy. This process is a key mechanism in galaxy evolution and has significant implications for the development of quasars, the interaction of galaxies, and the broader cosmic structure.
Outflows: Outflows refer to the streams of material, such as gas and dust, that are expelled from a celestial object like a star or a galaxy. These outflows play a crucial role in various astrophysical processes, impacting star formation, the evolution of galaxies, and the dynamics of interstellar medium. They can be driven by mechanisms like stellar winds, supernova explosions, or active galactic nuclei, influencing both the immediate environment and larger scale galactic structures.
Photoionization: Photoionization is the process in which an atom or molecule absorbs a photon and subsequently ejects one or more of its electrons, resulting in the formation of a positively charged ion. This phenomenon plays a critical role in shaping the characteristics of the interstellar medium and influences the feedback mechanisms in galaxy co-evolution. It is especially important in regions with high-energy radiation, such as around young stars, where it can lead to significant changes in the surrounding gas and dust.
Quenching of star formation: Quenching of star formation refers to the process that leads to a significant decrease or complete halt in the formation of new stars in galaxies. This phenomenon is crucial for understanding galaxy evolution, as it impacts the growth, structure, and eventual fate of galaxies. Quenching can result from various mechanisms, including feedback processes from supernovae, active galactic nuclei, or environmental effects such as galaxy mergers and interactions.
Radiation Pressure: Radiation pressure is the force exerted by electromagnetic radiation on a surface, resulting from the momentum carried by photons. This phenomenon plays a crucial role in various astrophysical processes, including the dynamics of stars and the interaction between radiation and matter, influencing galaxy evolution and feedback mechanisms.
Radiative Feedback: Radiative feedback refers to the processes by which the energy emitted by stars and other celestial objects affects their surrounding environments and influences subsequent star formation and galaxy evolution. This interaction plays a crucial role in regulating the balance of energy within galaxies, affecting temperature, density, and the dynamics of gas clouds, thereby contributing to the co-evolution of galaxies and their stellar populations.
Starbursts: Starbursts are regions of intense star formation within galaxies, characterized by the rapid birth of massive stars over a short period of time. This phenomenon often occurs when galaxies interact or merge, triggering gravitational instabilities that compress gas and dust, leading to a surge in star creation. The resulting energy output from these massive stars can significantly influence the surrounding environment and contribute to galaxy evolution.