6.3 Galaxy mergers
12 min read•august 20, 2024
Galaxy mergers are cosmic collisions that shape the universe. These events, ranging from minor interactions to major collisions, play a crucial role in galaxy evolution. They influence star formation, morphology, and the growth of supermassive black holes.
Understanding galaxy mergers helps us unravel the history of cosmic structures. By studying their types, stages, and effects, we gain insights into how galaxies grow and change over time. From creating elliptical galaxies to triggering starbursts, mergers leave lasting impacts on the cosmic landscape.
Types of galaxy mergers
- Galaxy mergers play a crucial role in the evolution and growth of galaxies, shaping their morphology, star formation rates, and overall properties
- The classification of galaxy mergers is based on the gas content and mass ratio of the merging galaxies, which significantly influence the outcome and characteristics of the merger
Wet vs dry mergers
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- involve gas-rich galaxies with significant amounts of cold gas and ongoing star formation
- These mergers often trigger intense bursts of star formation (starbursts) due to the compression and cooling of gas during the interaction
- occur between gas-poor galaxies, typically involving elliptical galaxies or galaxies that have already exhausted their gas supply
- Dry mergers do not result in significant star formation enhancement and primarily lead to the growth of stellar mass and size of the merged galaxy
Minor vs major mergers
- Minor mergers have a mass ratio greater than 1:3, where a smaller galaxy merges with a larger one
- These mergers can cause tidal disturbances and trigger moderate star formation but do not drastically alter the morphology of the larger galaxy
- Major mergers involve galaxies of comparable mass, with a mass ratio less than 1:3
- Major mergers have a more profound impact on galaxy morphology, often resulting in the or significantly altering the structure of the merging galaxies
- These mergers can also trigger intense starbursts and lead to the rapid growth of the merged galaxy
Stages of galaxy mergers
- Galaxy mergers progress through distinct stages, each characterized by specific physical processes and observable features
- Understanding these stages is crucial for interpreting observations of merging galaxies and studying their evolution
Pre-merger galaxy pair
- Before the merger begins, galaxies may exist in close pairs or groups, gravitationally bound but not yet interacting strongly
- These pre-merger pairs can be identified through their proximity and similar redshifts, indicating a shared cosmic environment
- Studying pre-merger pairs helps constrain the initial conditions and properties of galaxies before the merger process commences
Tidal interactions and bridges
- As galaxies approach each other, start to distort their morphologies, leading to the formation of , bridges, and other features
- Tidal tails are elongated streams of stars and gas that extend from the galaxies, formed by the gravitational pull of the interacting galaxies
- are structures that connect the two galaxies, allowing the exchange of material between them
- These tidal features are key indicators of ongoing galaxy interactions and provide insights into the merger dynamics
Coalescence and final merger
- In the final stage of the merger, the galaxies coalesce into a single merged entity
- During this stage, the remaining gas and stars from both galaxies are redistributed, leading to a reorganization of the galaxy's structure
- The intense gravitational interactions can trigger a peak in star formation activity, known as a
- The properties of the merged galaxy, such as its morphology and star formation rate, depend on the initial conditions of the merging galaxies and the details of the merger process
Impact on galaxy morphology
- Galaxy mergers have a profound impact on the morphology of galaxies, transforming their appearance and structural properties
- The outcome of a merger depends on factors such as the mass ratio, gas content, and orbital parameters of the merging galaxies
Formation of elliptical galaxies
- Major mergers between two spiral galaxies can result in the formation of an elliptical galaxy
- During the merger, the ordered rotational motion of the stars in the spiral galaxies is disrupted, leading to a more random and pressure-supported system
- The merged galaxy typically has a smooth, featureless appearance and lacks the distinct spiral arms and disk structure of its progenitor galaxies
- This process is thought to be a primary mechanism for the formation of massive elliptical galaxies in the universe
Enhancement of spiral structure
- Minor mergers or can enhance the spiral structure in a galaxy
- The gravitational perturbations induced by the interacting galaxy can trigger the formation or amplification of spiral arms
- This process can lead to the appearance of grand-design spiral patterns, where the spiral arms are more prominent and well-defined compared to isolated galaxies
- Enhanced spiral structure is often associated with increased star formation activity along the spiral arms
Creation of irregular galaxies
- Some mergers result in the formation of irregular galaxies, which lack a well-defined structure and often exhibit asymmetric or chaotic morphologies
- Irregular galaxies can arise from mergers between galaxies of unequal masses or from complex, multi-galaxy interactions
- These galaxies may show signs of tidal debris, clumps of star formation, and distorted shapes that deviate from the regular spiral or elliptical morphologies
- Studying irregular galaxies provides insights into the diverse outcomes of galaxy mergers and the role of dynamical processes in shaping galaxy evolution
Effect on star formation rates
- Galaxy mergers can have a significant impact on the star formation rates (SFRs) of the involved galaxies
- The gravitational interactions and tidal forces during mergers can trigger or suppress star formation, depending on the specific conditions of the merger
Merger-induced starbursts
- Wet mergers, particularly major mergers, can induce intense bursts of star formation known as starbursts
- The between the merging galaxies compresses and shocks the gas, leading to the rapid collapse of molecular clouds and the formation of new stars
- Starbursts can increase the SFR by orders of magnitude compared to the pre-merger galaxies, resulting in a significant increase in the luminosity and infrared emission of the system
- Merger-induced starbursts are thought to play a crucial role in the rapid buildup of stellar mass in galaxies and the formation of massive elliptical galaxies
Quenching of star formation
- In some cases, galaxy mergers can lead to the suppression or
- This can occur through various mechanisms, such as the removal of gas from the galaxies via tidal stripping or galactic winds
- The intense gravitational interactions during mergers can also disrupt the gas distribution and prevent the formation of new stars
- Dry mergers, which involve gas-poor galaxies, do not typically result in enhanced star formation and may even contribute to the quenching of residual star formation
- The quenching of star formation in post-merger galaxies can lead to the formation of passive, red elliptical galaxies with little ongoing star formation activity
Role in galaxy evolution
- Galaxy mergers play a fundamental role in the hierarchical growth and evolution of galaxies over cosmic time
- Mergers are a key driver of galaxy assembly, influencing the mass, size, and morphology of galaxies
Hierarchical galaxy formation
- In the of , galaxies grow through a series of mergers and accretion events
- Smaller galaxies merge to form larger systems, which in turn can merge with other galaxies to create even more massive structures
- This process is thought to be a primary mechanism for the formation of massive galaxies, particularly elliptical galaxies
- Hierarchical galaxy formation is supported by observations of galaxy mergers at various cosmic epochs and the increasing prevalence of massive galaxies in the early universe
Growth of massive galaxies
- Galaxy mergers contribute to the growth of massive galaxies by combining the stellar populations and dark matter halos of the merging systems
- Major mergers can lead to a rapid increase in the stellar mass and size of the merged galaxy
- Minor mergers, while less dramatic, can still contribute to the gradual growth of galaxies over time
- The merger history of a galaxy can be inferred from its morphology, stellar populations, and kinematic properties
- Studying the merger-driven growth of galaxies helps constrain models of galaxy evolution and provides insights into the assembly of the most massive galaxies in the universe
Observational evidence
- Observational evidence of galaxy mergers can be found through various techniques, providing crucial insights into the merger process and its impact on galaxy evolution
- These observations span a wide range of wavelengths and reveal different aspects of merging systems
Disturbed galaxy morphologies
- One of the most direct indicators of ongoing galaxy mergers is the presence of disturbed or irregular morphologies
- Merging galaxies often exhibit tidal tails, bridges, and asymmetric features that deviate from the regular spiral or elliptical structures of isolated galaxies
- These morphological disturbances arise from the gravitational interactions between the merging galaxies and can be detected in optical and infrared imaging
- Studying the morphology of merging galaxies provides information about the merger stage, mass ratio, and orbital parameters of the interacting systems
Tidal tails and shells
- Tidal tails are elongated streams of stars and gas that extend from merging galaxies, formed by the tidal forces during the interaction
- These tails can reach distances of several hundred kiloparsecs and are often visible in deep optical imaging
- Tidal shells are another feature associated with galaxy mergers, appearing as concentric arc-like structures surrounding the merged galaxy
- Shells are thought to form from the phase-wrapping of stars and gas during the merger process and can persist for several billion years after the merger
- The presence and properties of tidal tails and shells provide valuable information about the merger history and dynamics of galaxies
Ultra-luminous infrared galaxies (ULIRGs)
- (ULIRGs) are systems with extremely high infrared luminosities, typically exceeding solar luminosities
- ULIRGs are often associated with gas-rich major mergers, where the intense star formation activity is obscured by dust, leading to strong infrared emission
- The high infrared luminosity of ULIRGs is attributed to the merger-induced starburst, which can consume gas at rates of hundreds to thousands of solar masses per year
- Studying ULIRGs provides insights into the extreme environments and physical processes that occur during major mergers and their role in galaxy evolution
- Many ULIRGs are also found to host active galactic nuclei (AGN), suggesting a link between mergers, starbursts, and the growth of supermassive black holes
Simulations of galaxy mergers
- Numerical play a crucial role in understanding the complex physical processes and outcomes of galaxy mergers
- These simulations allow researchers to study mergers in a controlled environment, explore parameter spaces, and make predictions that can be compared with observations
Numerical simulation techniques
- Various numerical techniques are employed to simulate galaxy mergers, including N-body simulations, hydrodynamical simulations, and semi-analytic models
- N-body simulations focus on the gravitational dynamics of stars and dark matter, treating them as collisionless particles
- Hydrodynamical simulations incorporate the gas component and solve the equations of fluid dynamics alongside gravity, enabling the study of gas dynamics, star formation, and feedback processes
- Semi-analytic models combine dark matter halo merger trees with analytical prescriptions for baryonic physics to simulate galaxy formation and evolution on cosmological scales
Reproducing observed merger properties
- Simulations of galaxy mergers aim to reproduce the observed properties of merging systems, such as their morphology, star formation rates, and gas distribution
- By tuning the initial conditions and physical parameters of the simulations, researchers can match the observed features of specific merging galaxies or populations
- Simulations have been successful in reproducing tidal tails, bridges, and other morphological disturbances observed in merging galaxies
- They have also provided insights into the triggering and evolution of merger-induced starbursts, the formation of elliptical galaxies, and the growth of supermassive black holes
- Comparing simulations with observations helps constrain the physical models and improves our understanding of the merger process and its impact on galaxy evolution
Merger rates and environment
- The frequency and properties of galaxy mergers depend on various factors, including redshift and the large-scale environment in which galaxies reside
- Studying merger rates and their dependence on these factors provides insights into the cosmic history of galaxy assembly and the role of mergers in shaping galaxy populations
Dependence on redshift
- Merger rates are known to evolve with redshift, with higher merger frequencies observed in the early universe compared to the present day
- Observations have shown that the fraction of galaxies undergoing mergers increases significantly at higher redshifts (z > 1), reaching values of 20-30% or more
- This trend is consistent with the hierarchical model of galaxy formation, where mergers are more common in the early universe as galaxies assemble and grow over time
- The decline in merger rates towards lower redshifts reflects the decreasing availability of merger partners and the stabilization of galaxy structures
Role of galaxy clusters
- The large-scale environment, particularly galaxy clusters, plays a significant role in shaping merger rates and properties
- Galaxy clusters are the largest gravitationally bound structures in the universe, containing hundreds to thousands of galaxies
- The high galaxy densities and relative velocities in clusters can influence the frequency and nature of galaxy mergers
- Mergers in clusters are often more frequent than in isolated environments due to the increased likelihood of galaxy interactions
- However, the high relative velocities of galaxies in clusters can also make mergers less efficient, as encounters may be too fast for significant tidal interactions to occur
- The merger rate in clusters is also affected by the dynamical state of the cluster, with merging clusters exhibiting enhanced merger activity compared to relaxed clusters
Supermassive black hole growth
- Galaxy mergers play a crucial role in the growth and evolution of supermassive black holes (SMBHs) residing at the centers of galaxies
- Mergers can trigger the accretion of gas onto SMBHs, leading to their rapid growth and the activation of active galactic nuclei (AGN)
Black hole mergers
- When two galaxies with central SMBHs merge, the black holes themselves can eventually coalesce into a single, more massive SMBH
- The merger of SMBHs is a multi-stage process, beginning with the initial galaxy merger and culminating in the final of the black holes
- During the galaxy merger, the SMBHs sink to the center of the merged galaxy through and form a binary system
- The binary SMBH system can further shrink through stellar interactions and gravitational wave emission, ultimately leading to their merger
- The merger of SMBHs can release a tremendous amount of energy in the form of gravitational waves and can result in the recoil of the merged SMBH
Merger-driven gas inflow
- Galaxy mergers can drive the inflow of gas towards the central regions of the merged galaxy, fueling the growth of SMBHs
- The gravitational torques and tidal forces during the merger can cause gas to lose angular momentum and flow inwards, forming an accretion disk around the SMBH
- This merger-driven gas inflow can trigger a phase of rapid SMBH growth, as the black hole accretes matter at high rates
- The enhanced accretion activity can lead to the activation of an AGN, with the SMBH powering luminous emission across the electromagnetic spectrum
- Merger-driven SMBH growth is thought to be a key mechanism for explaining the observed correlations between SMBH mass and host galaxy properties, such as the relation
Future merger prospects
- Looking ahead, several exciting prospects exist for studying galaxy mergers in the local universe and beyond
- These future merger events offer unique opportunities to observe the merger process in unprecedented detail and gain new insights into galaxy evolution
Milky Way-Andromeda collision
- One of the most anticipated future merger events is the collision between our Milky Way galaxy and the Andromeda galaxy (M31)
- Current measurements suggest that the Milky Way and Andromeda are on a collision course, with the merger expected to occur in approximately 4-5 billion years
- The Milky Way-Andromeda collision will be a , given the comparable masses of the two galaxies
- Simulations predict that the merger will result in the formation of a giant elliptical galaxy, often referred to as "Milkomeda" or "Milkdromeda"
- The merger will have significant implications for the structure and evolution of the Local Group of galaxies and will provide a unique opportunity to study a major merger event in our cosmic neighborhood
Merger relics in nearby galaxies
- Many nearby galaxies show evidence of past merger events, known as merger relics
- These relics can include tidal tails, shells, and other morphological features that persist long after the merger has concluded
- Studying merger relics in nearby galaxies allows us to reconstruct their merger histories and understand the long-term impact of mergers on galaxy evolution
- Advances in observational techniques, such as deep imaging and integral field spectroscopy, are enabling detailed studies of merger relics and their properties
- By combining observations of merger relics with simulations, we can gain insights into the merger process and its role in shaping the galaxies we observe today
- Future observations of nearby galaxies with upcoming facilities, such as the James Webb Space Telescope and the Extremely Large Telescopes, will provide unprecedented views of merger relics and further our understanding of galaxy evolution
Key Terms to Review (31)
Active Galactic Nucleus: An active galactic nucleus (AGN) is a region at the center of some galaxies that emits an exceptionally high amount of energy, often outshining the rest of the galaxy. This phenomenon is typically associated with supermassive black holes that accrete matter, leading to the emission of intense radiation across various wavelengths, including radio, infrared, optical, and X-rays. AGNs are crucial in understanding galaxy evolution and play a significant role in the structure and dynamics of galaxies.
Albert Einstein: Albert Einstein was a theoretical physicist known for developing the theory of relativity, fundamentally changing our understanding of space, time, and gravity. His contributions have laid the groundwork for modern astrophysics and cosmology, influencing concepts such as redshift, gravitational lensing, and the cosmological constant.
Coalescence: Coalescence refers to the process where two or more entities combine to form a single, unified entity. In the context of galaxies, it specifically describes how galaxies merge over time due to gravitational attraction, leading to the formation of larger galactic structures. This phenomenon plays a crucial role in shaping the evolution of galaxies and is a fundamental aspect of cosmic interactions.
Cosmic evolution: Cosmic evolution refers to the gradual development of the universe from its initial state shortly after the Big Bang through various phases, including the formation of galaxies, stars, and planets. It encompasses the changes and processes that have occurred over billions of years, leading to the diverse structures and phenomena we observe today, such as galactic cannibalism and galaxy mergers, which play significant roles in shaping galaxies and their interactions over cosmic time.
Creation of irregular galaxies: The creation of irregular galaxies refers to the formation of galaxies that do not have a distinct, regular shape, often resulting from gravitational interactions and mergers with other galaxies. These galaxies typically exhibit chaotic structures, lacking the defined arms or elliptical shapes seen in spiral and elliptical galaxies. Irregular galaxies are essential for understanding galaxy evolution, as they can provide insights into the processes that shape galactic morphology and star formation.
Distorted galaxies: Distorted galaxies are galaxies that have undergone significant changes in their structure and appearance due to gravitational interactions with other galaxies. These interactions often occur during galaxy mergers, where the gravitational forces can pull and stretch the shapes of the galaxies involved, leading to features like tidal tails, bridges, and irregular forms. Such distortions provide valuable insights into the dynamics of galaxy formation and evolution, revealing the complex processes that shape our universe.
Dry mergers: Dry mergers refer to the process of two galaxies merging with minimal gas content, resulting in a primarily stellar interaction. These types of mergers typically happen in older galaxies where the gas has already been depleted due to star formation or feedback processes, and they primarily involve the gravitational interplay of the stars within the galaxies rather than significant new star formation. Dry mergers often lead to the formation of larger elliptical galaxies, and they play a crucial role in galactic evolution over cosmic time.
Dynamical Friction: Dynamical friction is a process that occurs in gravitational systems, where the motion of stars or other celestial bodies is influenced by their interactions with surrounding matter, leading to a gradual loss of energy and orbital decay. This phenomenon plays a crucial role in various astrophysical processes, such as the evolution of galaxy structures, the merging of galaxies, and the interactions between galaxies in a cluster.
Enhancement of spiral structure: Enhancement of spiral structure refers to the phenomenon where interactions during galaxy mergers amplify the existing spiral arms in galaxies, making them more pronounced and intricate. This enhancement often occurs as gravitational forces redistribute gas, dust, and stars, leading to increased star formation activity along the newly defined spiral arms, which can significantly alter the galaxy's appearance and dynamics.
Formation of elliptical galaxies: The formation of elliptical galaxies refers to the processes that lead to the development of these galaxy types, characterized by their smooth, featureless light profiles and an absence of significant amounts of gas and dust. These galaxies typically form through the merging of smaller galaxies, where the gravitational interactions can strip gas and create a more uniform distribution of stars, resulting in the dense and spheroidal structure observed in elliptical galaxies.
Galactic Cannibalism: Galactic cannibalism is the process where a larger galaxy merges with and consumes a smaller galaxy. This phenomenon plays a key role in the evolution and growth of galaxies over time, often leading to the formation of elliptical galaxies as they acquire mass from their smaller counterparts. As galaxies collide and merge, they can significantly alter their structures and star formation activities, influencing the overall dynamics of the universe.
Galaxy formation: Galaxy formation is the process through which galaxies evolve from small density fluctuations in the early universe into the vast structures we observe today. This complex process involves gravitational interactions, dark matter, star formation, and cosmic evolution, contributing to the diverse types of galaxies seen in the universe. Key factors in galaxy formation include the role of dark matter in shaping galaxy structures, the creation and dynamics of HII regions where new stars are born, the application of the virial theorem to understand galaxy stability, and how galaxy mergers influence their growth and morphology.
Gravitational interaction: Gravitational interaction refers to the force of attraction that exists between two masses due to their mass and the distance separating them. This force plays a crucial role in shaping the dynamics of celestial bodies, influencing their motion, behavior, and interactions with each other. Gravitational interactions are fundamental in understanding phenomena such as tidal effects and the merging of galaxies, which can lead to significant changes in their structures and compositions.
Hierarchical model: The hierarchical model is a framework that describes the formation and evolution of structures in the universe, particularly galaxies, in a tiered fashion. It suggests that smaller systems, like dwarf galaxies, merge together to form larger systems over time, leading to the complex structures we observe today. This model plays a crucial role in understanding galaxy mergers and galactic cannibalism, which are processes where larger galaxies grow by incorporating smaller ones.
Major merger: A major merger refers to the significant collision and subsequent amalgamation of two galaxies, typically of comparable size, leading to the formation of a single, larger galaxy. These mergers can significantly alter the structure, dynamics, and star formation activities within the involved galaxies and are crucial for understanding galaxy evolution.
Merger tree: A merger tree is a graphical representation that illustrates the hierarchical relationships and evolutionary paths of galaxies, detailing how they merge over time. It helps to visualize the history of galaxy formation, showing how smaller galaxies combine to form larger structures. Understanding merger trees is crucial for exploring the role of dark matter halos and the processes involved in galaxy mergers and galactic cannibalism.
Merger-induced starburst: A merger-induced starburst refers to a rapid and intense period of star formation that occurs when two galaxies collide and merge. During this process, the gravitational interactions between the galaxies trigger gas clouds to collapse and form new stars at an accelerated rate. This phenomenon is significant in understanding how galaxy mergers can influence the evolution of galaxies and contribute to the overall star formation history of the universe.
Minor merger: A minor merger is a type of galaxy merger where a smaller galaxy merges with a significantly larger galaxy, resulting in minimal disruption to the larger galaxy's structure. In these mergers, the smaller galaxy typically contributes less mass and fewer stars, making the event less impactful compared to major mergers. Such interactions can lead to the formation of new star clusters and influence the larger galaxy's evolution, but they do not drastically change its overall morphology.
Observational Surveys: Observational surveys are systematic methods of gathering data about celestial objects by observing them from a distance without manipulating any variables. In the study of galaxies, these surveys help astronomers collect vital information regarding the structure, composition, and behavior of galaxies, particularly during events like galaxy mergers. Observational surveys play a crucial role in understanding how galaxies evolve over time and how interactions between them influence their development.
Pre-merger galaxy pair: A pre-merger galaxy pair refers to two galaxies that are in close proximity to each other and are on a collision course, before the actual merger takes place. These pairs are significant because they provide critical insights into the processes of galaxy evolution and the interactions that occur before galaxies combine, including gravitational influences and star formation triggered by their mutual gravitational pull.
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 within a galaxy. This phenomenon can be caused by various mechanisms, including environmental factors such as galaxy mergers, which can trigger changes in gas dynamics and star formation rates, ultimately affecting the evolutionary trajectory of galaxies.
Simulations: Simulations are computational models that replicate complex systems or processes to study their behavior and outcomes under various conditions. In the context of galaxy mergers, simulations help astronomers understand how galaxies interact, merge, and evolve over time, revealing insights into their structure and dynamics.
Starburst activity: Starburst activity refers to an exceptionally high rate of star formation occurring in a galaxy, typically driven by interactions such as mergers or gravitational influences. This phenomenon leads to the rapid conversion of gas into new stars, often outpacing the galaxy's typical star formation rate by a significant margin. Starburst activity plays a critical role in shaping the evolution and structure of galaxies, especially during periods of hierarchical merging or galaxy mergers.
Tidal bridges: Tidal bridges are elongated structures of stars and gas that form between two galaxies as they interact gravitationally during a merger. These features arise from the tidal forces exerted by the gravitational pull of the merging galaxies, pulling material from one galaxy to another. Tidal bridges can provide insights into the dynamics of galaxy mergers and the transfer of mass and energy between galaxies.
Tidal Forces: Tidal forces are the gravitational interactions between celestial bodies that result in the distortion of their shapes, leading to phenomena such as tides on planets and moons. These forces are crucial in understanding how galaxies interact, affecting their morphology and environment, as well as playing a significant role in the dynamics of tidal interactions and galaxy mergers.
Tidal interactions: Tidal interactions refer to the gravitational effects that one astronomical body has on another, leading to changes in shape, structure, and sometimes even orbits. These interactions can significantly influence the evolution of galaxies, shaping their morphology and star formation rates, especially in the context of irregular galaxies, secular evolution, and galaxy mergers.
Tidal tails: Tidal tails are elongated structures of stars, gas, and dust that are pulled out from galaxies due to gravitational interactions during close encounters or mergers. These features are important indicators of tidal interactions, showcasing the effects of gravitational forces between galaxies as they influence each other’s shapes and distributions of matter. Tidal tails can reveal the history of galaxy mergers, highlighting processes like galactic cannibalism and hierarchical merging as galaxies evolve over time.
Timescale: Timescale refers to the duration of events in the universe, often measured in years, millions of years, or even billions of years. It is crucial for understanding cosmic processes, especially when studying events like galaxy mergers that can take extensive periods to unfold. Grasping timescales helps in appreciating how galaxies evolve and interact over time, influencing their structure and properties.
Ultra-luminous infrared galaxies: Ultra-luminous infrared galaxies (ULIRGs) are a class of galaxies that emit an exceptionally high amount of their energy in the infrared part of the electromagnetic spectrum, typically over 10^12 solar luminosities. These galaxies are often formed through intense star formation and are frequently linked to galaxy mergers, where the interaction between two or more galaxies can trigger significant bursts of star formation and activate their central supermassive black holes, resulting in the ULIRG phenomenon.
Vera Rubin: Vera Rubin was an influential American astronomer known for her pioneering work on the rotation curves of galaxies, which provided critical evidence for the existence of dark matter. Her groundbreaking observations helped reshape our understanding of galaxy dynamics and the structure of the universe, connecting closely to various concepts including galaxy formation and the cosmic web.
Wet mergers: Wet mergers refer to the process of merging galaxies where both galaxies involved retain significant amounts of gas and dust, leading to intense star formation during and after the collision. This type of merger is crucial in understanding galaxy evolution, as it often results in the creation of new stars and can dramatically change the structure of the merging galaxies. Wet mergers are especially relevant in discussions about galactic cannibalism, hierarchical merging, and the overall dynamics of galaxy mergers.