Galaxy interactions are the dominant trigger for local type 2 quasars
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J C S Pierce↗
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Search for interacting galaxy clusters from SDSS DR-17 employing optimized friends-of-friends algorithm and multimessenger tracers
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Tejas Oak↗
The Galaxy activity-interaction connection. II - Radio observations
VLA results are presented for southern interacting galaxies at 6 and 20 cm, with a view to the detection and classification of the nature of radio emission in a set of advanced-interaction disk galaxies. Maps of radio emission are given for the 42 interacting systems in the sample, as well as 10 control systems, and radio properties are compared with optical and IR properties; the radio in all of the present interacting galaxies are attributable to properties associated with a burst of star formation due to galaxy interaction.
Smith, Eric P.↗
The dynamical interaction between galaxies and intracluster gas in clusters of galaxies
The interaction between the hot gas inferred to exist in clusters of galaxies and the interstellar medium of a spherical galaxy has been studied by means of time-dependent numerical hydrodynamics. Galaxies moving at transonic speeds with respect to the ambient medium lose 80% to 90% of their interstellar gas before a crossing time has elapsed. The amount of gas remaining is consistent with current observational limits to the gas content of elliptical galaxies. Negligible heating of the intracluster gas results from this process. Implications of these results for spiral galaxies with halos, radio sources in clusters of galaxies, and globular clusters in galactic halos are discussed.
Lea, S. M.↗
The galaxy activity-interaction connection. I - Optical observations
As part of an investigation into the triggering of nuclear radio emission in interacting galaxies, new multicolor, broadband data are presented from a subset of Arp-Madore Catalog galaxies selected on the basis of their optical morphology - systems with loops and/or tails. The CTIO 4 m is used to obtain images in B, V, R, and I for the purpose of performing synthetic aperture photometry. Isophotal ellipse fitting to the more regular objects in the sample is also performed to quantify their isophotal deviation from purely elliptical morphologies. Color index maps for the galaxies are constructed, and the optical morphologies, broadband colors, and detailed photometric properties as well as the IRAS fluxes for the galaxies are discussed. These data are used to obtain a rough measure of the level of activity present in these systems.
Smith, Eric P.↗
Two-dimensional caustics in disturbed galaxy disks
Interacting galaxies show a variety of exotic morphologies besides the well-known rings, spirals, and bars. It is proposed that many of these can be identified with nonlinear, caustic structures that are known from singularity theory to be generic in collisionless dynamics. A simple kinematical model for stellar orbits is used to study the development of caustic waveforms in galaxy disks following impulsive, nonaxially symmetric (collisional) disturbances. It appears that all of the caustics known from singularity theory to be generic in two dimensions develop as transient forms in at least some moderately off-center collisions. The more complex, higher-order caustics appear most prominently in the more off-center and larger amplitude disturbances. It is further suggested that the highly nonlinear caustic waves may play an important role in interaction-induced star formation.
Struck-Marcell, Curtis↗
Global effects of interactions on galaxy evolution
Recent observations of the evolutionary properties of paired and interacting galaxies are reviewed, with special emphasis on their global emission properties and star formation rates. Data at several wavelengths provide strong confirmation of the hypothesis, proposed originally by Larson and Tinsley, that interactions trigger global bursts of star formation in galaxies. The nature and properties of the starbursts, and their overall role in galactic evolution are also discussed.
Kennicutt, Robert C., Jr.↗
Bar-spheroid interaction in galaxies
N-body simulation and linear analysis is employed to investigate the secular evolution of barred galaxies, with emphasis on the interaction between bars and spheroidal components of galaxies. This interaction is argued to drive secular transfer of angular momentum from bars to spheroids, primarily through resonant coupling. A moderately strong bar, having mass within corotation about 0.3 times the enclosed spheroid mass, is predicted to shed all its angular momentum typically in less than about 10 exp 9 yr. Even shorter depletion time scales are found for relatively more massive bars. It is suggested either that spheroids around barred galaxies are structured so as to inhibit strong coupling with bars, or that bars can form by unknown processes long after disks are established. The present models reinforce the notion that bars can drive secular evolution in galaxies.
Hernquist, Lars↗
Infrared images of merging galaxies
Infrared imaging of interacting galaxies is especially interesting because their optical appearance is often so chaotic due to extinction by dust and emission from star formation regions, that it is impossible to locate the nuclei or determine the true stellar distribution. However, at near-infrared wavelengths extinction is considerably reduced, and most of the flux from galaxies originates from red giant stars that comprise the dominant stellar component by mass. Thus near infrared images offer the opportunity to study directly components of galactic structure which are otherwise inaccessible. Such images may ultimately provide the framework in which to understand the activity taking place in many of the mergers with high Infrared Astronomy Satellite (IRAS) luminosities. Infrared images have been useful in identifying double structures in the nuclei of interacting galaxies which have not even been hinted at by optical observations. A striking example of this is given by the K images of Arp 220. Graham et al. (1990) have used high resolution imaging to show that it has a double nucleus coincident with the radio sources in the middle of the dust lane. The results suggest that caution should be applied in the identification of optical bright spots as multiple nuclei in the absence of other evidence. They also illustrate the advantages of using infrared imaging to study the underlying structure in merging galaxies. The authors have begun a program to take near infrared images of galaxies which are believed to be mergers of disk galaxies because they have tidal tails and filaments. In many of these the merger is thought to have induced exceptionally luminous infrared emission (cf. Joseph and Wright 1985, Sanders et al. 1988). Although the optical images of the galaxies show spectacular dust lanes and filaments, the K images all have a very smooth distribution of light with an apparently single nucleus.
Wright, G. S.↗
The Oort cloud and the Galaxy - Dynamical interactions
The results of recent dynamical studies of the Oort cloud and its interaction with the Galaxy are discussed. Various studies which used Monte Carlo simulations to investigate the evolution of comets in the Oort cloud and the manner in which they are injected into the planetary region are reviewed. Work done on perturbation of cometary orbits by stars, interstellar clouds, and the Galaxy is examined. The growing consensus that there is a massive inner Oort cloud with a population up to 100 times that of the dynamically active outer cloud is addressed. Variations on the Oort hypothesis are discussed. It is argued that speculations about the existence of a small unseen solar companion star or a tenth planet causing periodic comet showers from the inner Oort cloud are not supported by dynamical studies or analyses of the terrestrial and lunar cratering record. Evidence for Oort clouds around other stars is summarized.
Weissman, Paul R.↗
H II regions in the dwarf galaxy UGC-A 86
The uncertain nature of the dwarf irregular galaxy UGC-A 86 (VIIZw009) makes it a very interesting object for studying star formation at the low end of the galaxy luminosity function. Saha and Hoessel (1991) find that this object is composed of two main parts, one of which appears more resolved than the other. The more resolved component has an excess of blue stars, suggesting that it is currently undergoing star formation. Thus, they argue that UGC-A 86 could be either a superposition of unrelated galaxies, two interacting galaxies, or a single galaxy. However, surface photometry performed by Richter et al. (1991) indicates that it is a single galaxy with an exponential luminosity profile. Richter et al. also find UGC-A 86 to be extremely dusty and to be associated with the infrared source IRAS 3550+6657. The uncertainty is compounded by the large ambiguity in the distance, though a heliocentric H1 velocity of 80 plus or minus 7 km s(sup -1) suggests that it is either a member of the Local Group or perhaps the IC 342 group. A distance of 1.5 Mpc and a reddening of E(B - V) = 0.65 is adopted. UGC-A 86 in H-alpha was observed in order to measure its current star formation rate. This is part of a larger project to study the star formation rates and histories of a complete sample of dwarf galaxies in the Local Group and other nearby groups. The H region luminosity function and size distribution for UGC-A 86 are presented and compared with previous observations of similar dwarf galaxies.
Miller, Bryan W.↗
Theoretical models of gas dynamics and star formation in interacting ring galaxies
A series of one and two dimensional hydrodynamic simulations of a ring wave in interstellar gas disks was completed. These calculations included nonlinear source terms to model the effects of interstellar interactions and star formation, as well as the spatial-temporal gas flow. Toomre's kinematical model was merged with the Arnold, Shandarin, and Zeldovich 'pancake' theory of caustics in galaxy formation. The resulting theory can describe almost all the structure in restricted three-body simulations of single-pass collisions, even with multi-component potentials. Off-center galactic collisions were studied to understand the dynamics involved. Multi-color optical and near-infrared observations of faint tidal features were performed in about two dozen interacting galaxies selected from the Arp atlas. This sample provided evidence for ongoing star formation in tidal structures, and even enhancements of star formation in some cases. The task of assembling the data for gas-rich, late-type galaxies, was undertaken to see if a more coherent picture of the gas distribution would emerge from the more complete data. Analytic solutions of the equations with subsonic flows to balance gas consumption for expulsion form a galactic fountain were also derived.
Struck-Marcell, Curtis↗
Dynamical interactions of galaxy pairs
Here the author briefly reviews the dynamics of sinking satellites and the effect of companions on elliptical galaxies. The author then discusses recent work on interacting disk systems, and finally focuses on a favorite interacting pair, NGC 5194/5195.
Athanassoula, E.↗
Nuclear winds in active elliptical galaxies. I - Interaction
The interaction of a supersonic wind generated by an active nucleus, a nuclear wind, with the hot interstellar medium of an elliptical host galaxy is investigated. We survey the basic time and spatial scales of this interaction through a study covering the range of probable wind and galaxy parameters. The evolving wind/ISM interaction is detailed, with the conclusion that a true equilibrium state is never possible due to long cooling times. Alteration of the wind by mass loading is considered, and a relationship between nuclear winds and central stellar clusters in this context is outlined. The nuclear wind will fundamentally alter the interstellar medium of the host galaxy. Powerful radio galaxies and quasars can evacuate the entire ISM of their host galaxy. In an isolated elliptical galaxy, winds from moderately powerful radio galaxies will either be confined to within about a kpc or evacuate the entire hot ISM. Even in the relatively high pressure ISM of elliptical galaxies winds containing only 1 percent-10 percent of the radiant luminosity of the active nucleus will extend to the narrow-line region. Therefore, nuclear winds are likely to control the properties of the narrow-line emission.
Smith, Steven J.↗
Star formation and dynamics in starburst nuclei
A simple model is presented for gas inflow through a disk galaxy driven by interacting galaxies through the action of a non-axisymmetric disturbance acting on the disk whose gas is modelled as an ensemble of gas clouds. Cloud collisions, as well as being a vital process in forcing gas inflow to the center of the disk, are also assumed to generate massive stars. This ever increasing rate of gas flow toward the center of the galaxy and the associated rapid increase in cloud collisions lead to a centrally concentrated starburst. Starbursts have important consequences for the immediate environment of galaxies. Mildly collimated outflows can be driven by a combination of multiple supernovae and OB star winds. Jets associated with activity in the galactic nucleus can interact strongly with a starburst environment.
Norman, Colin A.↗
Interacting binary galaxies. VI - The fast encounter of NGC 2672 and NGC 2673 (Karachentsev 175, Arp 167)
The isolated pair of interacting ellipticals NGC 2672/2673 (Arp 167; Karachentsev 175), whose line-of-sight relative velocity is about 520 km/s, is studied. This very unequal mass system features two low surface brightness plumes emerging from the secondary galaxy NGC 2673. Photometric data on the pair are described, and the distortions in the galaxies and their photometric properties are discussed. Spectroscopic observations of the pair and the velocity structures derived from these are addressed. A physical solution for the pair is presented and explained.
Balcells, Marc↗
Interacting binary galaxies. V - NGC 4782/4783 (3C 278): Unbound colliders, not a supermassive pair
CCD imaging data of the elliptical galaxies NGC 4782 and NGC 4783 have been analyzed along with published spectroscopic measurements in order to develop a viable interaction model for this system. The best-fit model suggests that the binary orbit was hyperbolic before the encounter, but that the energy loss during the collision has led to a loosely bound system. The total system mass in the region occupied by the luminous matter is shown to be 1.4 x 10 to the 12th solar masses. The results support the previous theory that the internal velocity dispersions of colliding galaxies tend to increase just past closest approach.
Borne, Kirk D.↗
The H I content of non-isolated galaxies
It seems obvious that the evolution of star formation rate and hence of gas content in galaxies strongly depends on their environment. It reveals itself in particular in enhanced star formation or even in a strong burst of activity of massive stars often observed in interacting galaxies. Nevertheless it should be noted that the time scale for the gas to be exhausted in these galaxies is unknown even approximately. To clarify a role of surroundings in the evolution of disk galaxies we should compare the H I content of isolated and non-isolated galaxies otherwise similar by their properties. It is concluded that there are no systematic differences between H I content in isolated and non-isolated late-type galaxies; in spite of the differences of star formation rates their hydrogen mass is determined by slowly evolving kinematic parameters of the disk. Enhanced star formation in interacting galaxies, if it lasts long enough, must have an initial mass function enriched in massive stars in order not to significantly reduce the supply of gas. Certainly these conclusions are not valid for galaxies which are members of rich clusters such as Virgo or Coma, where H I-deficiency really exists, possibly due to the interaction of interstellar H I with hot intergalactic gas.
Zasov, Anatoli V.↗