Galaxy Merger
Encyclopedia, Science News & Research Reviews
Introduction
Galactic mergers can occur when two (or more) galaxies collide. They are the most intense type of galactic interaction. Gravitational interactions between galaxies and friction between gas and dust have a large impact on participating galaxies. The precise effects of such coalescence depend on various parameters such as collision angles, velocities and relative sizes/compositions, and is currently a very active research area. Galactic mergers are important because the rate of galactic mergers is a fundamental measure of galactic evolution. Merger rates also provide astronomers clues about how galaxies have grown over time.
Scholarly Articles
...We report detected anomalies of interest including galaxy mergers, tidal features, and extreme star-forming galaxies.....
...An excess for the respective AGN host galaxies in the subsequently derived major merger fractions would then indicate that AGN are predominantly triggered by such galaxy mergers.....
...We crossmatch our sample of 10 CL galaxies with the largest existing MaNGA AGN catalog and identify seven in it; two of the remaining three are galaxy mergers and the final one is an AGN candidate.....
...Galaxy mergers can potentially amplify the magnetic fields from their progenitors, making the magnetic fields dynamically important.....
...Galaxy mergers are traditionally one of the favoured mechanisms for the transformation of spiral galaxies to spheroids and for quenching star formation.....
...In simulations, certain configurations of galaxy mergers are known to produce this type of rotation.....
...Both the presence of a molecular disc with ongoing star-formation in a starburst ring, and the signatures of a minor merger, are in agreement with the scenario where galaxy mergers produce gas destabilization, feeding both star-formation and AGN activity.....
...We find that while dynamical NS-PBH formation could account for the GW170817 event, the rate is highly dependent on unknown density contrast factors and could potentially be affected by galaxy mergers.....
...Galaxy mergers are a mechanism for rapid quenching of star formation.....
...Processes such as galaxy mergers, disk instabilities, and environmental effects can produce such strong star formation variability.....
...We link the SMBH population to the fraction of quasars fbin resulting from Galaxy mergers that pair SMBHs to a binary.....
...We trace the evolution of off-centre massive black holes (MBHs) in dwarf galaxies using cosmological hydrodynamical simulations, and show that the reason for off-centre locations is mainly due to galaxy–galaxy mergers.....
...The largest rates expected in galaxy mergers (104 − 105 M yr−1) become accessible once the accretor is supermassive (M & 104 M ).....
...In contrast, Type III profiles result from galaxy mergers, extended star-forming discs or the late formation of a steeper, inner disc.....
...Galaxy mergers are instrumental in dictating the final mass, structure, stellar populations, and kinematics of galaxies.....
...Galaxy mergers are thought to be one of the main mechanisms of the mass assembly of galaxies in the Universe, but there is still little direct observational evidence of how frequent they are at z & 4.....
...5$), indicating a population of young stars and/or an enhanced dust mass, probably due to relatively recent galaxy merger(s).....
...The search and study of close pairs of supermassive black holes (SMBHs) is important in the study of galaxy mergers which can possibly trigger active galactic nucleus (AGN) activity, and in the context of their evolution into the gravitational wave emitting regime.....
...This diversity indicates that a wide array of physical processes must be at work at this epoch, first and foremost, those of galaxy mergers.....
...At this point, we are very much in need of large datasets with high-quality high-resolution spectra and tailored high-resolution hydrodynamical simulations of galaxy mergers.....
...Starburst galaxies are often found to be the result of galaxy mergers.....
...Coalescing massive black hole binaries (MBHBs) of $10^{4-7} \rm M_{\odot}$, forming in the aftermath of galaxy mergers, are primary targets of the space mission LISA, the {\it Laser Interferometer Space Antenna}.....
...Binary supermassive black holes (SMBH) are expected to form naturally during galaxy mergers.....
...Large galaxy surveys have demonstrated that galaxy-galaxy mergers can dramatically change the morphologies, star formation rates (SFRs) and metallicities of their constituents.....
...The manifestation of feedback in shocks is particularly important to examine in galaxy mergers, where violent interactions of gas takes place in the interstellar medium during the course of the galactic collision.....
...Simulations show that galaxy mergers cause gas inflows, triggering nuclear starbursts, increasing the central stellar density.....
...In addition, we find some hints of gas inflow or galaxy-galaxy merger in the majority of our sample.....
...In this paper, we infer upper limits on the lifetime of binary black holes of |$10^{5-6}\, {\rm M_\odot }$| and up to |$10^8\, {\rm M_\odot }$|, forming in galaxy mergers, exploring two underlying stellar density profiles, by Dehnen and by Prugniel & Simien, and by exploiting local scaling relations between the mass of the black holes and several quantities of their hosts.....
...Galaxy mergers and interactions are expected to play a significant role leading to offsets between gas and stellar motions in galaxies.....
...The FIR sees a strong evolution in which disks dominate at $z\le 1$ and starbursts (triggered by both galaxy mergers and disk instabilities, in an even mix) dominate at higher redshifts, even out to $z=10$.....
...Galaxy mergers and interactions are an integral part of our basic understanding of how galaxies grow and evolve over time.....
...Galaxy mergers are expected to have a significant role in the mass assembly of galaxies in the early universe, but there are very few observational constraints on the merger history of galaxies at z > 2.....
...At high AGN luminosities, galaxy mergers and interactions play an important role in AGN triggering and feeding.....
...In a previous work, we investigated with direct N-BODY simulations the evolution of TDE rates of SMBHB systems in galaxy mergers of equal mass.....
...The average intrinsic X-ray spectral slope indicates efficient accretion, potentially driven by galaxy mergers, and the column densities suggest one-third of the sample has significant X-ray absorption.....
...Our model reproduces the distribution of local galaxy morphologies, with bulges formed predominantly through galaxy mergers for low-mass galaxies, disc-instabilities for galaxies with $M_\ast\simeq10^{10}$-$10^{11.....
...On the other hand, the flat dependence of the outside-in quenching on halo mass could be a mixed result of ram-pressure stripping and galaxy mergers.....
...I have used the Horizon-AGN simulation to study the effect of galaxy mergers on the stellar populations and central super-massive black holes of galaxies over cosmic time.....
...We measure the fraction of galaxy-galaxy mergers in two clusters at $z\sim2$ using imaging and grism observations from the {\it Hubble Space Telescope}.....
...We present image-based evolution of galaxy mergers from the Illustris cosmological simulation at 12 time-steps over 0.....
...The two extended components could be a galaxy with an internal absorption feature, a galaxy merger, or two galaxies at different redshifts.....
...Adopting literature estimates for (1) the excess rate of galaxy-galaxy mergers in intermediate/high-density environments and (2) the average amount of $j_\ast$ loss per merger event, we investigated the possibility that galaxy mergers are mainly responsible for the loss of angular momentum in higher density environments.....
...Finally, within the limited volume of Romulus25, we find no evidence for a connection between black hole growth and galaxy mergers, on any timescale and at any redshift.....
...These trends with $M_{\rm *}$ can be understood in the context of differential feedback efficiency by supernovae in low-mass galaxies, and by galaxy mergers, AGN feedback or halo mass quenching in higher-mass galaxies.....
...However, their growth might have been impacted by galaxy mergers and BH feedback so that they cannot be treated as tracers of the early seed BH population.....
...Supermassive black hole (SMBH) binaries form due to galaxy mergers and minor accretion events.....
...Galaxy mergers are a fundamental part of galaxy evolution.....
...The presence of two KDCs most probably are evidence of a major merger that has altered the structure of FCC47 significantly, indicating the important role of galaxy mergers in forming the complex kinematics in the galaxy-NSC system.....
...We also find that galaxy mergers are critical points from which large (as much as a factor of 2) variations in quantities such as the galaxy stellar mass can grow.....
Description
During the merger, the stars and dark matter of each galaxy become influenced by the approaching galaxy. As the merger approaches the late stages, the gravitational potential (and thus the shape of the galaxy) begins to change rapidly, leading to large changes in star orbits and the loss of traces of previous orbits. This process is called "violent relaxation". For example, when two disk galaxies collide, they begin with regular rotation of the stars in the planes of the two separate disks. During coalescence, that ordered motion is converted into random energy (“thermalization”). The resulting galaxy is dominated by stars orbiting the galaxy in a complex and randomly interacting orbital network, which is observed in elliptical galaxies. Mergers are also where extreme amounts of star formation take place. Depending on the gas content of each galaxy and its redshift, the star formation rate (SFR) during large-scale mergers can reach thousands of solar masses worth of new stars each year. A typical merged SFR is less than 100 new solar masses per year. This is large compared to our galaxy, which produces only a few new stars each year (about 2 new stars). In a galactic merger, stars rarely come close enough to actually collide, but the giant molecular cloud falls rapidly into the center of the galaxy, where it collides with other molecular clouds. These collisions cause these clouds to condense and form new stars. This phenomenon can be seen in the merger of galaxies in the nearby universe. But this process is more pronounced during the mergers that form most of the elliptical galaxies we see today, from billions of years ago when there was much more gas (and therefore more molecular clouds) within the galaxy. It is believed to have happened 10 billion years ago. Also, gas clouds away from the galactic center collide with each other, creating shocks that stimulate the formation of new stars within the gas clouds. As a result of all this violence, galaxies tend to have little available gas to form new stars after a merger. Thus, after a galaxy undergoes a massive merger and after billions of years, there are few young stars left in the galaxy (see Star Evolution). This is what we see in elliptical galaxies today, with little molecular gas or young stars. This is thought to be because elliptical galaxies are the end product of large-scale mergers, during which most of the gas is used up, and more stars form after the merger disappears. A galaxy merger can be simulated on a computer to learn more about it. galaxy formation. Accounting for all gravitational forces, hydrodynamics and dissipation of interstellar gas, star formation from gas, energy and mass released into the interstellar medium by supernovae, we can initially track galaxy pairs of any morphological type. . . A library of such galaxy merger simulations can be found on the GALMER website. A study led by Jennifer Lotz of the Space Telescope Science Institute in Baltimore, Maryland, created computer simulations to better understand images taken by the Hubble Space Telescope. Lotz's team attempted to explain a wide range of possible mergers, from merging pairs of galaxies of equal mass to interactions between giant and small galaxies. The researchers also analyzed the different orbits of the galaxies, their potential for collisions, and how the galaxies are oriented with respect to each other. In total, the group devised 57 different merging scenarios and studied merging from 10 different viewing angles. One of the largest galaxy mergers ever observed consisted of four elliptical galaxies in the cluster CL0958+4702. It may form one of the largest galaxies in the universe.
Categories
Galactic mergers can be classified into different groups depending on the properties of the merged galaxy, such as their number, relative size, and gas richness.
= By number =
Mergers can be classified by the number of galaxies involved in the process. binary merge Two interacting galaxies merge. multiple mergers Merge 3 or more galaxies.
= By size =
Mergers can be classified by the extent to which they change the size and shape of the largest galaxies involved. small merger A merger is small when one of the galaxies is significantly larger than the others. Larger galaxies often "eat" smaller galaxies, absorbing most of their gas and stars, but have little other significant effect on large galaxies. Our home galaxy, the Milky Way, is now thought to be absorbing several smaller galaxies in this way, including the Canis Major dwarf galaxy and possibly the Magellanic Cloud. The Virgo Stellar Stream is believed to be mostly the remnants of a dwarf galaxy that merged with the Milky Way. large-scale merger A massive merger of two spiral galaxies of roughly the same size. If they collide at the right angles and velocities, they will likely coalesce, driving off much of the dust and gas through various feedback mechanisms, including a phase in which an active galactic nucleus exists. This is believed to be the driving force behind many quasars. The end result is an elliptical galaxy, and many astronomers hypothesize that this is the main mechanism that produces the ellipse. One study found that large galaxies merged on average once in the last 9 billion years. Smaller galaxies merged with larger galaxies more often. Note that the Milky Way and Andromeda galaxies are predicted to collide in about 4.5 billion years. The expected result of the merger of these galaxies is that they will be similar in size and thus larger, transforming them from two "grand design" spiral galaxies into a (possibly) giant elliptical galaxy.
= By gas richness =
Mergers can be classified according to the degree to which the gas (if any) carried in and around the merging galaxies interacts. wet merge Wet mergers occur between gas-rich galaxies (“blue” galaxies). Wet mergers typically cause massive star formation, transform disk galaxies into elliptical galaxies, and trigger quasar activity. dry merger Mergers between gas-poor galaxies (“red” galaxies) are called dry. Dry mergers typically do not significantly alter the rate of star formation in galaxies, but they may play an important role in increasing stellar mass. wet amalgamation Wet mergers occur when enough gas is present to drive significant star formation, but not enough to form globular clusters, by combining the same two galaxy types described above (“blue” galaxies and “red” galaxies). galaxies). mixed merger Mixed mergers occur when gas-rich and gas-poor galaxies (“blue” and “red” galaxies) merge.
Merger history trees
Standard cosmological models predict that a single galaxy formed from the successive coalescence of several or many dark matter halos, in which the gas cooled to create a star at the center of the halo. Forming into optically visible objects historically identified as galaxies. 20th century. Modeling of the mathematical graphs of the coalescence of these dark matter halos, and thus of the corresponding star formation, was initially either by analyzing purely gravitational N-body simulations or by numerical realizations of statistical (“semi-analytical”) formulas. processed by using At the 1992 Observational Cosmology Conference in Milan, Lukema, Quinn, and Peterson presented the first coalescence history tree of dark matter halos extracted from cosmological N-body simulations. These coalescence history trees were combined with formulas for star formation rate and evolutionary assemblage synthesis to yield composite luminosity functions (statistics for the number of intrinsically bright or faint galaxies) for galaxies at various cosmological epochs. rice field. Given the complex dynamics of dark matter halo coalescence, a fundamental problem in modeling coalescence history trees is to define when a halo at one time step is a descendant of a halo at a previous time step. Roukema's group decided to define this relationship by requiring that the halo at the later time step contains exactly 50% or more of the particles in the halo at the earlier time step. This guaranteed that any halo could have at most one descendant between two time steps. This galaxy formation modeling approach rapidly computes models of galaxy ensembles with synthetic spectra and corresponding statistical properties comparable to observations. Separately, Lacey and Cole showed at the same 1992 conference how to combine the Press-Schecter formalism with dynamic friction to generate Monte statistically. Carlo realized the coalescence history tree of the dark matter halo and the formation of the corresponding stellar nucleus (galaxy) of the halo. Kaufman, White, and Gaidredoni extended this approach in 1993 to incorporate semi-analytical formulas for hypothetical cooling of gas, star formation, reheating of gas from supernovae, and the transformation of disk galaxies into elliptical galaxies. rice field. Subsequently, both the Kaufmann group and Okamoto and Nagashima adopted a merged history tree approach derived from N-body simulations.
Examples
Some of the galaxies in the process of merging, or believed to have formed through a merger, are: antenna galaxy mouse galaxy Centaur A NGC 7318
See also
Collision of the Andromeda Star and the Milky Way Galaxy bulge (astronomy) Formation and evolution of galaxies interacting galaxies List of stellar streams mass defect pea galaxy
External links
Andromeda Caught in Galactic Collision – NBC News "GALMER: Galaxy Merger Simulation"
supermassive black hole
Scholarly Articles
...We consider the possible mechanisms driving this variability, and conclude that orbital motion of two supermassive black holes – result from a recent galaxy merger – is a possible explanation.....
...A galaxy merger is expected to cause the formation of a supermassive black hole (SMBH) binary, which itself eventually coalesces through the anisotropic emission of gravitational waves.....
...Supermassive black hole binaries (SMBHBs) should form frequently in galactic nuclei as a result of galaxy mergers.....
...The most accepted scenario for the evolution of massive galaxies across cosmic time predicts a regulation based on the interplay between AGN feedback, which injects large amounts of energy in the host environment, and galaxy mergers, being able to trigger massive star formation events and accretion onto the supermassive black holes.....
...The flat stellar density cores of massive elliptical galaxies form rapidly due to sinking supermassive black holes (SMBH) in gas-poor galaxy mergers.....
...We present here a self-consistent cosmological zoom-in simulation of a triple supermassive black hole (SMBH) system forming in a complex multiple galaxy merger.....
...Although thousands of galaxy mergers are known, only a handful of sub-kiloparsec-scale supermassive black hole (SMBH) pairs have been confirmed so far, leaving a huge gap between the observed and predicted numbers of such objects.....
...Binary supermassive black hole (SMBH) systems result from galaxy mergers, and will eventually coalesce due to gravitational wave (GW) emission if the binary separation can be reduced to.....
...Galaxy mergers occur frequently in the early Universe1 and bring multiple supermassive black holes (SMBHs) into the nucleus, where they may eventually coalesce.....
active galactic nuclei
Scholarly Articles
...While theory and simulations indicate that galaxy mergers play an important role in the cosmological evolution of accreting black holes and their host galaxies, samples of Active Galactic Nuclei (AGN) in galaxies at close separations are still small.....
...Observational searches for dual active galactic nuclei (dAGNs) at kiloparsec separations are crucial for understanding the role of galaxy mergers in the evolution of galaxies.....
..., dual active galactic nuclei) and candidates have been found in galaxy mergers, only three kpc-scale triple AGN candidates are known.....
...Major galaxy mergers can trigger nuclear activities and are responsible for high-luminosity quasi-stellar objects/active galactic nuclei (QSOs/AGNs).....
...Research over the past decade has shown diminishing empirical evidence for major galaxy mergers being a dominating or even important mechanism for the growth of supermassive black holes in galaxies and the triggering of optically or X-ray selected active galactic nuclei (AGN).....
...The question of whether galaxy mergers are linked to the triggering of active galactic nuclei (AGN) continues to be a topic of considerable debate.....
Dwarf Galaxy Merger
Scholarly Articles
...Here we present a detailed multiwavelength investigation of star formation and BH activity in the low-metallicity dwarf–dwarf galaxy merger Mrk 709.....
...We suggest that the Virgo Overdensity (VOD) of stars in the stellar halo is the result of a radial dwarf galaxy merger that we call the Virgo Radial Merger.....
...A natural assumption for modeling the gravitational potential is that GCs accreted in the same dwarf galaxy merger event move at the present time on similar orbits in the host galaxy and should therefore have similar actions.....
...We describe a population of young star clusters (SCs) formed in a hydrodynamical simulation of a gas-rich dwarf galaxy merger resolved with individual massive stars at sub-parsec spatial resolution.....
Rich Galaxy Merger
Scholarly Articles
...These results imply that, like in the non-rotating case, the final masses of the progenitors of direct collapse black holes range in distinct intervals depending on the scenario considered: 10^5 Msun < M < 10^6 Msun for primordial atomically cooled haloes; 10^6 Msun < M < 10^9 Msun for metal-rich galaxy mergers.....
...Prograde metal-poor stars originate largely from a single LMC/SMC-mass gas-rich galaxy merger, typically 7 − 12.....
...To answer this question, we performed a series of numerical simulations of gas-rich galaxy mergers at high redshift.....
...Dynamical black hole mass measurements in some gas-rich galaxy mergers indicate that they are overmassive relative to their host galaxy properties.....
Major Galaxy Merger
Scholarly Articles
...OH megamasers (OHMs) are rare, luminous masers found in gas-rich major galaxy mergers.....
...These events, which we call 'off-center', can only be produced from a close encounter between CO binaries and SMBHBs; hence the detection of such merger events would indicate the existence of nearby SMBHBs, and in particular with high mass ratio, produced in the aftermath of a major galaxy merger.....
...Major galaxy mergers can trigger nuclear activities and are responsible for high-luminosity quasi-stellar objects/active galactic nuclei (QSOs/AGNs).....
...Research over the past decade has shown diminishing empirical evidence for major galaxy mergers being a dominating or even important mechanism for the growth of supermassive black holes in galaxies and the triggering of optically or X-ray selected active galactic nuclei (AGN).....
Frequent Galaxy Merger
Scholarly Articles
...Morphological features seen in nearby galaxies, such as stellar disks, bulges, and spiral arms, require time to form and would be disturbed by the frequent galaxy mergers that occurred at early times.....
...Morphological features seen in nearby galaxies, such as stellar disks, bulges, and spiral arms, require time to form and would be disturbed by the frequent galaxy mergers that occurred at early times.....
Nearby Galaxy Merger
Scholarly Articles
...Rather, the dwarfs interact with gas thrown off by nearby galaxy mergers or streams extending from neighboring galaxies.....
...The hard X-ray spectrum of the Northeast nucleus is consistent with a heavily absorbed AGN, making Mrk 273 another example of a dual AGN in a nearby galaxy merger.....
Galaxy Merger Rate
Scholarly Articles
...The detection of a gravitational-wave background at nanohertz frequencies can tell us if and how supermassive black holes merge, and inform our knowledge of galaxy merger rates and supermassive black hole masses.....
...At intermediate length scales (10 kpc-1 Mpc) WAVES will probe the size and mass distribution of galaxy groups, as well as the galaxy merger rates, in order to directly measure the assembly of dark matter halos and stellar mass.....
...We find the GW amplitude is very sensitive to the galaxy merger rate.....
...The observation of gravitational-waves from merging supermassive black holes will be transformative: the detection of a low-frequency gravitational-wave background can tell us if and how supermassive black holes merge, inform our knowledge of galaxy merger rates and supermassive black hole masses, and enable the possibility of detecting new physics at nanohertz frequencies.....
Galaxy Merger Fraction
Scholarly Articles
...We study the galaxy merger fraction and its dependence on star formation mode in the 5.....
...We estimate the evolution of the galaxy–galaxy merger fraction for M ⋆ > 1010.....
...From this analysis, we propose a new set of criteria to select close pairs of galaxies along with a new corrective term to be applied to the computation of the galaxy merger fraction.....
Galaxy Merger Simulation
Scholarly Articles
...To achieve that, we choose a set of minor merger models from the publicly available GalMer library of galaxy merger simulations.....
...We present a comprehensive suite of high-resolution (parsec-scale), idealised (non-cosmological) galaxy merger simulations (24 runs, stellar mass ratio ~2.....
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Definition & Meaning
Galaxy
Noun
- a splendid assemblage (especially of famous people tufted evergreen perennial herb having spikes of tiny white flowers and glossy green round to heart-shaped leaves that become coppery to maroon or purplish in fall (astronomy
Merger
Noun
- the combination of two or more commercial companies an occurrence that involves the production of a union