Showing papers on "Galaxy merger published in 1990"
TL;DR: In this paper, a systematic alignment of 20-60 faint background galaxy images has been detected, centered on foreground galaxy clusters of high velocity dispersion, and the background galaxy population is selected by its extreme blue B-R color.
Abstract: A gravitational lens distorts most background galaxies by stretching along a circle centered on the lens. This systematic alignment of 20-60 faint background galaxy images has been detected, centered on foreground galaxy clusters of high velocity dispersion. The background galaxy population is selected by its extreme blue B-R color. At a limiting surface brightness of 29 B mag/sq arcsec, there are over 30 background galaxies/sq arcmin per mag anywhere in the sky, which is sufficient to map statistically the dark matter distribution in a foreground cluster. The dark matter is apparently correlated (center and radial extent) with the cluster red light, suggestive of a baryonic origin or dissipative coupling. The existence of a high percentage of lens-distorted faint blue galaxies sets a lower limit of approximately 0.9 to this background galaxy population mean redshift. 13 refs.
343 citations
TL;DR: In this article, the authors explored the consequences of binary star mergers on the assumption that a merger can be approximated by a mass-transfer event which occurs on a time scale shorter than that given by the Eddington accretion limit.
Abstract: The theory of binary star evolution suggests that about 10 percent of all main-sequence binary systems should evolve into a close pair of light white dwarfs which merge within a Hubble time. This paper explores the consequences of such mergers on the assumption that a merger can be approximated by a mass-transfer event which occurs on a time scale shorter than that given by the Eddington accretion limit. The evolution of He + He mergers and of CO + He and of hybrid + He mergers are discussed. The birthrate of helium degenerate pairs which merge in less than a Hubble time is estimated, and the space density of low-luminosity merger products currently present in the Galaxy is predicted. It is shown that the evolutionary tracks of models of simulated mergers pass through the region in the H-R diagram occupied by subdwarfs, but that the predicted space density of merger products exceeds by over a factor of three the space density of subdwarf estimated form the known sample of such stars. 61 refs.
114 citations
TL;DR: The mechanism proposed by Kormendy (1984) for the formation of counterrotating cores in elliptical galaxies is investigated using self-consistent numerical simulations of mergers between a high and a low-luminosity elliptical galaxy as discussed by the authors.
Abstract: The mechanism proposed by Kormendy (1984) for the formation of counterrotating cores in elliptical galaxies is investigated using self-consistent numerical simulations of mergers between a high- and a low-luminosity elliptical galaxies. The conditions for a counterrotation to appear are determined, observational properties of the remnants are described, and the evolution of the structural and kinematic parameters of the larger galaxy is analyzed. It is shown that a counterrotation results only when the merging orbits are retrograde, due to a large change in the secondary spin during the merger.
113 citations
TL;DR: In this article, the expected evolution of quasars is calculated using the dynamics of merging galaxies and the assumption that the birth rate of quasar is proportional to the rate of mergers.
Abstract: The expected evolution of quasars is calculated using the dynamics of merging galaxies and the assumption that the birth rate of quasars is proportional to the rate of mergers. The merger rate is described using a modification of the Press-Schechter theory. As a specific model, the luminosity of a quasar is assumed to be proportional to its host galaxy's halo mass, and the amount of gas supplied per merger is independent of the quasar's luminosity, implying a lifetime that is inversely proportional to luminosity. The main strength of the model is its relation to the dynamics of clustering. Its main weaknesses are the poorly constrained relations between host galaxies and quasars. 64 refs.
92 citations
TL;DR: In the near-infrared, extinction and the effects of hot young stars are much reduced as mentioned in this paper, and they have obtained? images of six galaxies which are believed to be mergers of disk galaxies.
Abstract: THEORETICAL studies indicate that in collisions between disk galaxies, dynamical friction and subsequent relaxation will eventually produce a mass distribution indistinguishable from that of an elliptical galaxy. However, there are also theoretical and observational arguments against this process1,2. Schweizer's pion-eering paper3, which showed that the V-light profile of the merging galaxy NGC7252 is indeed well fitted by the r1/4 de Vaucouleurs law, remains the only observational evidence in support of this idea. In most candidate mergers the optical structure is complicated because of emission from star-forming regions and obscuration by dust lanes, and there is no overall resemblance to ellipticals. In the near-infrared, extinction and the effects of hot young stars are much reduced. Accordingly we have obtained ? images of six galaxies which are believed to be mergers of disk galaxies. Two of the six, NGC2623 and Arp220, appear to obey the r1/4 law to the limits of our images, offering new support for the idea that mergers of spirals can evolve into elliptical-like objects.
82 citations
TL;DR: In this paper, the expected ionization produced during galaxy formation is analyzed in terms of highly model-independent metal production arguments and it is concluded that (if such galaxies are dust-free and transparent to ionizing photons) then at least 4(H 0/50 km/s Mpc)-cubed percent of galaxy formation would have to have occurred in this redshift range.
Abstract: The absence of any continuous Ly-alpha opacity from the intergalactic medium at z = 3-4.5 can be understood if a significant population of star-forming galaxies is present at these redshifts. It is shown that such galaxies can be present within the galaxy populations at B = 22 to 27. The expected ionization produced during galaxy formation is analyzed in terms of highly model-independent metal production arguments and it is concluded that (if such galaxies are dust-free and transparent to ionizing photons) then at least 4(H0/50 km/s Mpc)-cubed percent of galaxy formation would have to have occurred in this redshift range.
74 citations
TL;DR: In this article, high-resolution CO observations of the merging galaxies NGC 4038/39 (the "Antennae") have been made with the Owens Valley Millimeter Wave Interferometer.
Abstract: High-resolution CO observations of the merging galaxies NGC 4038/39 (the 'Antennae') have been made with the Owens Valley Millimeter Wave Interferometer. Three concentrations of CO emission were detected. In addition to masses of a few x 100 million solar masses at each nucleus, approximately 1.2 x 10 to the 9th solar masses of molecular gas was discovered in a 32 arcsec x 22 arcsec region where the two galaxies overlap. Within this region are four distinct clumps. These coincide with H-alpha, 10 microns, and radio continuum peaks, suggesting that they are extremely active sites of star formation. The galaxy interaction appears to have concentrated gas at the nuclei of NGC 4038 and NGC 4039 and to have engendered enhanced star formation activity in the region where their disks overlap. From estimates of the SFR in this overlap region, it is suggested that the gas will be completely depleted in 240 million yr.
74 citations
01 Jan 1990
TL;DR: In this article, a review of the early history of the subject and recent progress in understanding the six main types of galactic collisions is presented, with a focus on three issues: (1) the fascinating parallels that exist between the 1 Gyr old merger remnant NGC7252 and elliptical galaxies; (2) what new light the study of young (≲100 Myr) and old (≳ Gyr) starbursts is shedding on the formation of E and SO galaxies; and (3) the still fragmentary, but growing, evidence that even the bul
Abstract: Over the past two decades, our perception of galactic collisions and mergers has changed dramatically: once thought to be interesting but rare events, they are now perceived as some of the dominant processes governing galaxy formation and evolution. I shall first briefly review the early history of the subject and our recent progress in understanding the six main types of galactic collisions. Then I shall focus on three issues: (1) the fascinating parallels that exist between the 1 Gyr old merger remnant NGC7252 and elliptical galaxies; (2) what new light the study of young (≲100 Myr) and old (≳ Gyr) starbursts is shedding on the formation of E and SO galaxies; and (3) the still fragmentary, but growing, evidence that even the bulges of disk galaxies may have formed through mergers. As we shall see, it now seems likely that the present position of a galaxy in Hubble’s morphological sequence was determined mainly by the number and severity of mergers in its past history.
71 citations
TL;DR: The compact group H31 was identified by Hickson in 1982; it consists of four galaxies in close proximity, at least two of which (A and C) are interacting as mentioned in this paper.
Abstract: The compact group H31 was identified by Hickson in 1982; it consists of four galaxies in close proximity, at least two of which (A and C) are interacting. Red and H-alpha frames and long-slit spectroscopy identify at least three other close members of the group; an H I envelope encloses all galaxies. Nuclear spectra of galaxies A and C show velocity patterns characteristic of interacting galaxies as well as the broad 4650 A feature indicative of W-R stars. These features reveal that large numbers of massive stars formed more than 10 exp 6.5 yr ago. Other observed characteristics all suggest that H31 is in the process of merging to a single galaxy. H31 thus supports computations which indicate that galaxies in compact groups merge to form a single remnant. 52 refs.
56 citations
TL;DR: In this article, the IRAS data for a sample of nearby radio galaxies (z less than 0.13) are analyzed, and it is shown that most of the long-wavelength infrared emission comes from cool interstellar dust for almost all of the galaxies; these galaxies may contain large amounts (10 to the 8th - 10 to the 10th solar masses of interstelar matter).
Abstract: The IRAS data for a sample of nearby radio galaxies (z less than 0.13) are analyzed. Comparison of the infrared, radio, and optical data suggests that most of the long-wavelength infrared emission comes from cool interstellar dust for almost all of the galaxies; these galaxies may contain large amounts (10 to the 8th - 10 to the 10th solar masses of interstelar matter. About 15 percent of the galaxies show evidence for a hotter thermal component emitting at the shorter IRAS wavelengths; this could be due to dust in the inner regions of the galaxy heated by the active galactic nucleus.
TL;DR: In this paper, the evolution of black hole systems in multiple mergers of galaxies has been investigated, using a particular galaxy merger process with a continuous distribution of the black hole masses.
Abstract: The evolution of black hole systems in multiple mergers of galaxies has been investigated, using a particular galaxy merger process with a continuous distribution of the black hole masses. Two types of escapes represented the most common line of evolution: the nearly symmetric escapes and the one-sided escapes. Symmetric escapes dominate at low velocities, and one-sided escapes dominate at high velocities. An exception to this rule is made by those one-sided escape trails where the escape speed is low; the number of such trails is only about 10 percent of the number of symmetric escape trails. In the present form of the slingshot model, the degree of symmetry of the black hole separations from the center of the galaxy is very close to the degree of symmetry by which the lobes of the 3C double radio sources are placed relative to the center of the radio galaxy. 46 refs.
TL;DR: In this paper, a three-dimensional model is developed for gas clouds orbiting in the gravitational potential of a galaxy which, at some later time, is perturbed by the gravitational influence of another galaxy.
Abstract: A three-dimensional model is developed for gas clouds orbiting in the gravitational potential of a galaxy which, at some later time, is perturbed by the gravitational influence of another galaxy. As the strength of the interaction increases, the interstellar medium becomes more disturbed. The clouds collide at an increased rate and with larger velocities, so that the fraction of collisions which disrupt the clouds rises rapidly as the strength of the interaction increases. On the other hand, no large increases in the rate at which massive clouds are built up are found. Since interacting galaxies are observed to have star formation efficiencies which are about five times higher than those in isolated galaxies, it is concluded that the star formation induced by the interaction of two galaxies is related to the high-velocity, disruptive cloud-cloud collisions. 46 refs.
TL;DR: In this article, the available distances of galaxies are combined to produce a unified view of galaxy motions within the so-called great attractor (GA) region, including 253 galaxies within 40 deg of the nominal GA center.
Abstract: The available distances of galaxies are combined to produce a unified view of galaxy motions within the so-called great attractor (GA) region. The data base includes 253 galaxies within 40 deg of the nominal GA center. Spirals and ellipticals are grouped into clusters to reduce Malmquist bias. Checks are made for systematic errors in the motions of ellipticals that are correlated with cluster richness, structural parameters of the galaxies, or errors in Galactic absorption, and no significant effects on the observed large-scale motions are found. Other evidence strongly supporting the current distance indicators is reviewed, and arguments are presented in favor of the cosmic background radiation defining the correct velocity rest frame. The basic conclusion of the study is the affirmation of the fundamental correctness of the present body of measured galaxy motions. 49 refs.
01 Jan 1990
TL;DR: In this article, the authors review two topics which gave important new clues to the structure and formation of elliptical galaxies in the past two years: isophotal shapes and core kinematics.
Abstract: This review confines to two topics which gave important new clues to the structure and formation of elliptical galaxies in the past two years: isophotal shapes and core kinematics.
TL;DR: In this paper, a simulation de n corps is realized for the rest of galaxies coalescentes, based on the profil de la loi r 1/4 and l'evolution du rayon en fonction de la masse.
Abstract: Une simulation de n corps est realisee pour les restes de galaxies coalescentes. Le profil de la loi r 1/4 et l'evolution du rayon en fonction de la masse sont analyses
01 Jan 1990
TL;DR: In this article, the authors present the results of an imaging survey aimed at finding and cataloguing various kinds of fine structure in 74 nearby E + S0 galaxies, including ripples (shells), strongly boxy isophotes, X-structure, and plumes.
Abstract: We present the results of an imaging survey aimed at finding and cataloguing various kinds of fine structure in 74 nearby E + S0 galaxies More than half of the objects feature at least one of the following: ripples (“shells”), strongly boxy isophotes, X-structure, and plumes, thus suggesting a multi-component origin (mergers, accretions) for these galaxies The presence of fine structure correlates with spectral line strengths measured by Faber et al (1990): ellipticals with ripples, plumes, etc, tend to have stronger-than-average Hβ lines and weaker-than-average CN and Mg2 indices for their luminosity, suggesting that — compared to their featureless counterparts — they may have experienced more recent star formation
TL;DR: Using the recently completed Southern Sky Redshift Survey, in conjunction with measurements of the central surface brightness, the existence of segregation in the way galaxies of different morphology and surface brightness are distributed in space is investigated.
Abstract: Using the recently completed Southern Sky Redshift Survey, in conjunction with measurements of the central surface brightness, the existence of segregation in the way galaxies of different morphology and surface brightness are distributed in space is investigated. Results indicate that there is some evidence that low surface brightness galaxies are more randomly distributed than brighter ones and that this effect is independent of the well-known tendency of early-type galaxies to cluster more strongly than spirals. Presuming that the observed clustering was established at the epoch of galaxy formation, it may provide circumstantial evidence for biased galaxy formation. 24 refs.
TL;DR: In this paper, the outer rings of both NGC 6028 and Hoag-type galaxies may be formed through mechanisms related to the oval structures of the central cores, and a countereffect of the ring formation relating to a possible dissolution of barred structures is discussed briefly.
Abstract: Surface photometry has been done on the nearest and brightest Hoag-type galaxy, NGC 6028, which is known to be a peculiar galaxy consisting of a luminous core surrounded by a faint, apparently detached ring. Most of the Hoag-type galaxies are found to have oval-shaped cores, and it is suggested that the outer rings of both NGC 6028 and Hoag-type galaxies may be formed through mechanisms related to the oval structures of the central cores. A countereffect of the ring formation relating to a possible dissolution of barred structures is discussed briefly. The accretion hypothesis for the origin of outer rings is considered, and possible interactions between the accreting gas and the hot, X-ray emitting gas around elliptical galaxies are discussed. 60 refs.
01 Jan 1990
TL;DR: In this article, the effects of mass loss and initial abundance on the chemical yield of, and the evolution of, the high-mass stars are investigated, and it is shown that this is likely to be a bimodal process.
Abstract: The star-gas cycle is central to an understanding of the evolution of disk galaxies. In this paper, we investigate three key aspects. First, the effects of mass loss and initial abundance on the chemical yield of, and the evolution of, the high-mass stars. Second, we investigate star formation, and demonstrate that this is likely to be a bimodal process. The stars with masses 1M⨀ are formed predominantly in cloud-cloud collisions which destroy the parent clouds. Massive stars regulate the phase structure of the ISM in the galactic disks. The final sections investigate the chemical evolution of both our solar neighbourhood, and of the Magellanic Clouds. The hazy concept of “metallicity” is inappropriate to an understanding of chemical evolution. However, the metallicity - metallicity relationships may be used to put useful constraints on past populations of stars in these systems, and to lay the basis for a clearer understanding of the chemical evolution of other disk systems.
TL;DR: In this article, a study of the internal velocity structure of NGC 3656, a galaxy with several morphological signatures of being in an advanced merger stage, is presented, showing that the inner 1 kpc rotates around an axis roughly perpendicular to the rotation axis in the main body of the galaxy.
Abstract: A study is presented of the internal velocity structure of NGC 3656, a galaxy with several morphological signatures of being in an advanced merger stage Rotation curves obtained for two slit-position angles show that the inner 1 kpc rotates around an axis roughly perpendicular to the rotation axis in the main body of the galaxy There are indications that the galaxy is not dynamically relaxed at intermediate radii The presence of an orthorotating core in a dynamically young galaxy with a dust disk and a shell system provides strong evidence linking kinematically peculiar cores to mergers However, relating the various merger signatures in this system is not straightforward, as the core and the dust disk rotate around axes perpendicular to each other, which may indicate an independent origin
TL;DR: In this article, the IR-excess object NGC 6240 was observed with broadband BVR, Gunn z, i, H-alpha, forbidden N II (658.3-nm), and K images obtained at ESO and KPNO.
Abstract: Observations of the IR-excess object NGC 6240 are presented, including (1) broadband BVR, Gunn z, i, H-alpha, forbidden N II (658.3-nm), and K images obtained at ESO and KPNO; (2) 350-690-nm and 550-1100-nm long-slit spectra obtained at La Palma and ESO; and (3) 628.0-697.5-nm fiber-array spectra of the inner region obtained with the 4-m Mayall telescope at KPNO. The results are presented graphically and characterized in detail. Strong optical line emission is attributed to shocks between clouds in large-scale chaotic motion, and evidence found for an active Seyfert-1-type nucleus. There is only a moderate amount of star formation, and two central light concentrations are interpreted as the remnant nuclei of merging galaxies. It is suggested that the observed luminosity of NGC 6240 could be maintained for tens of Myr (without dominant starburst activity) by the energy stored in gas motion, assuming that the proportion of ionized gas is less than 0.0001. 41 refs.
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TL;DR: The main components of our Galaxy are (1) the disk (thin and thick), which is rapidly rotating; (2) the bulge; (3) the metal weak halo, which rotates very slowly, and (4) the dark corona, which provides most of the mass Near the sun, there is no rotationally intermediate population as discussed by the authors.
Abstract: The main components of our Galaxy are (1) the disk (thin and thick), which is rapidly rotating; (2) the bulge; (3) the metal weak halo, which rotates very slowly, and (4) the dark corona, which provides most of the mass Near the sun, there is no rotationally intermediate population
01 Jan 1990
TL;DR: In this article, the authors present results on mergers of equal-mass disk/halo galaxies and show how a merging encounter can funnel large amounts of gas to the remnant center, fueling a starburst or an active galactic nucleus.
Abstract: Self-consistent numerical models of interacting disk galaxies are now providing detailed answers to some key dynamical questions. Here I present recent results on mergers of equal-mass disk/halo galaxies. Such collisions produce remnants with many of the properties of ordinary elliptical galaxies. In particular, the remnants exhibit de Vaucouleurs’ luminosity profiles, tri-axial shapes supported by anisotropic velocities, and little or no rotation. Models including gas dynamics show how a merging encounter can funnel large amounts of gas to the remnant center, fueling a starburst or an active galactic nucleus.
01 Jan 1990
TL;DR: Toomre et al. as mentioned in this paper pointed out that it seems almost inconceivable that there was not a great deal of merging of sizable bits and pieces (including quite a few lesser galaxies) early in the career of every major galaxy, no matter what it looks like now.
Abstract: The conjecture about mergers that is cited above has been discussed in more detail by Chandrasekhar (1942) in his theory of dynamical friction. As Toomre (1977) points out: “It seems almost inconceivable that there wasn’t a great deal of merging of sizable bits and pieces (including quite a few lesser galaxies) early in the career of every major galaxy, no matter what it looks like now.” Observations by Zepf and Koo (1989) suggest that such interactions between galaxies may have been much more frequent in the past than they are now. If this view is correct then the galaxies we see today might bear little resemblance to the original population of primordial galaxies. It is noted in passing that most tidally distorted galaxies have nearby optical companions. It follows (van den Bergh 1969) that only a small fraction of all galaxies can consist entirely of dark matter.
TL;DR: In this article, the group of mostly faint galaxies surrounding the dumbbell galaxy NGC 4782/3 is examined and an estimate for an upper limit of the mass of the galaxies is obtained using the virial theorem.
Abstract: The group of mostly faint galaxies surrounding the dumbbell galaxy NGC 4782/3 is examined. Assuming that the group mass is negligible compared to the dumbbell galaxy, an orbit-independent estimate for an upper limit of the mass of the galaxies is obtained using the virial theorem. Spectroscopic observations of 13 galaxies in the group suggest that the group has mass values in the range (1.8-6) X 10 to the 13th/h solar mass. If mass is distributed as luminosity, the dumbbell galaxy has a total mass in the range (0.8-3) X 10 to the 13th/h solar mass. 21 refs.
01 Jan 1990
TL;DR: In this paper, the presence of a large complex of HI clouds moving at high velocity perpendicular to the disk of a spiral galaxy M101 has been detected, and it was shown that capture and infall of gas-rich, dwarf irregular galaxies may explain the M101 results.
Abstract: Recent observations of the nearby spiral galaxy M101 have revealed the presence of a large complex of HI clouds moving at high velocity perpendicular to the disk of that galaxy. Capture and infall of gas-rich, dwarf irregular galaxies may explain the M101 results. Observations of a number of systems with gas-rich companions, such as NGC 3359, or with associated, peculiar HI structures suggest that recurrent, episodic gas infall into galaxies may be taking place.
TL;DR: In this article, the authors presented the first systematic survey at optical wavelengths of galaxies with detected radio jets using CCD imaging and found that about 50% of the galaxies with radio jets have a large nearby companion and/or show peculiar optical morphology not detected in isolated ellipticals.
Abstract: This paper presents the first systematic survey at optical wavelengths of galaxies with detected radio jets using CCD imaging. About 50 percent of the sample of low-redshift galaxies with radio jets have a large nearby companion and/or show peculiar optical morphology not detected in isolated ellipticals. Forty-five percent of the objects have a companion galaxy at a distance shorter than 20 kpc. The multicomponent galaxies in the sample form a very homogeneous group with little gas and dust, while the isolated galaxies have more heterogeneous radio properties, with large amounts of gas and warm dust in a large fraction of these galaxies. Intrinsic differences between the multicomponent galaxies and the isolated ones are explained in terms of a different parent galaxy and interaction processes. It is concluded that, at least among galaxies with radio jets, the amount of gas available and the interactions could control the energy generation, producing a very well-defined type of radio source. 48 refs.