M. Thomasson's research while affiliated with Iowa State University and other places

Publications (54)

Article
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Hubble Space Telescope (HST) images of the galaxies NGC 2207 and IC 2163 show star formation and dust structures in a system that has experienced a recent grazing encounter. Tidal forces from NGC 2207 compressed and elongated the disk of IC 2163, forming an oval ridge of star formation along a caustic where the perturbed gas rebounded after its inw...
Article
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BIMA 12CO J = 1 → 0 observations are presented of the spiral galaxies NGC 5394 and NGC 5395 that have undergone a recent, grazing encounter. In NGC 5394 approximately 80% of the CO emission detected by BIMA is concentrated in the central 800 pc (FWHM) starburst region, and the rest is from a portion of the inner disk south and west of the central s...
Article
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H I, radio continuum, Fabry-Perot Hα, and 12CO J = 1 → 0 observations and broadband optical and near infrared images are presented of the interacting spiral galaxies NGC 5395 and NGC 5394. Kinematically, there are three important, separate components to the H I gas associated with this galaxy pair: (1) the main disk of NGC 5395, (2) a long, norther...
Article
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IC 2163 and NGC 2207 are interacting galaxies that have been well studied at optical and radio wavelengths and simulated in numerical models to reproduce the observed kinematics and morphological features. Spitzer IRAC and MIPS observations reported here show over 200 bright clumps from young star complexes. The brightest IR clump is a morphologica...
Chapter
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We use computer simulations of tidal interactions of spiral galaxies and find that the stronger the tidal perturbation by a companion, the more disk gas clouds are thrown into nucleus-crossing orbits and the greater their collision velocities in the disk. More intense and hotter IR emission would result, matching observations by Telesco, Wolstencro...
Article
IC 2163 and NGC 2207 are interacting galaxies that have been well studied at optical and radio wavelengths and simulated in numerical models to reproduce the observed kinematics and morphological features. Spitzer IRAC and MIPS observations reported here show over 200 bright clumps from young star complexes. The brightest IR clump is a morphologica...
Article
We present numerical hydrodynamical models of the collision between the galaxies IC 2163 and NGC 2207. These models extend the results of earlier work where the galaxy discs were modeled one at a time. We confirm the general result that the collision is primarily planar, that is, at moderate inclination relative to the two discs, and prograde for I...
Article
We propose IRAC and MIPS observations of the interacting galaxies IC 2163 and NGC 2207 in order to find and measure the properties of embedded young massive clusters (YMC), determine the luminosities and masses of clusters and gas in an extraordinary region that may contain a black hole inside a YMC, measure the dust temperatures and column densiti...
Article
In previous work we have established a relationship between the shape of the arms in grand-design spiral galaxies and the distribution of mass in their discs. Here we apply this relationship to derive disc mass distributions for five selected galaxies. Our preliminary results indicate that the disc mass--luminosity ratio is low, on average about 3...
Article
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We made radio, optical, and CO observations of three pairs of spiral galaxies involved in recent, grazing encounters and compared our data with numerical simulations. The tidal structures seen in the galaxy undergoing a prograde, in-plane encounter share a number of key features which are adequately explained by our simulations. It is shown that th...
Article
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Hubble Space Telescope observations in U, B, V, and I passbands of the interacting spiral galaxies IC 2163 and NGC 2207 are used to measure extinctions in the cloud and intercloud regions and ages and luminosities of the star-forming regions. The extinction in the part of NGC 2207 seen in projection against IC 2163 was determined by using the metho...
Article
The Hubble Heritage Project has the aim of providing the public with pictorially striking images of celestial objects obtained with NASA's Hubble Space Telescope. The Heritage team has made a 3-color mosaic of the interacting spiral galaxies IC 2163 and NGC 2207 from three pointings of the WFPC2 camera in UBVI passbands. The scientific investigator...
Article
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IC 2163 has a central eye-shaped ("ocular") structure with two long tidal arms indicative of a very recent, close, tidal encounter. It is partially obscured by its spiral companion NGC 2207. Numerical models (Elmegreen et al. 1995, ApJ, 453,139) suggest that perigalacticon occurred 40 Myr ago. We use UBVI images taken with the WFPC2 camera of HST t...
Article
We obtained H I , radio continuum, and 12 CO J = 1 → 0 observations at resolutions of 12″ to 33″ (= 2.9 - 8 kpc), and B, I, J, and K–band images, of the galaxy NGC 2535 and its small starburst companion NGC 2536. NGC 2535 has an ocular (eye-shaped) structure indicative of a recent, close, nonmerging encounter. Our observations reveal widespread hig...
Article
We present HI, CO and optical observations of the ocular galaxy NGC 2535 and its starburst companion NGC 2536. NGC 2535 has an ocular (eye--shaped) structure with two long tidal arms. Such morphologies are indicative of a very recent, close, non--merging encounter. They have been reproduced in numerical models when the orbit of the companion is pro...
Article
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Observations with the Hubble Space Telescope reveal an irregular network of dust spiral arms in the nuclear region of the interacting disk galaxy NGC 2207. The spirals extend from ~50 pc to ~300 pc in galactocentric radius, with a projected width of ~20 pc. Radiative transfer calculations determine the gas properties of the spirals and the inner di...
Article
A method to calculate the disc surface density of grand-design spiral galaxies is presented and applied to three galaxies: M 51, NGC 2997, and NGC 1566. Previous numerical simulations, of spontaneous and tidally induced spiral patterns in galaxies, have shown that the shape of the spiral arms is independent of the origin of the pattern. Furthermore...
Article
Full-text available
H I, radio continuum, and 12CO J=1→0 observations at resolutions of 12" to 33" (=2.9-8 kpc), and B, I, J, and K-band images, are presented of the galaxy NGC 2535 and its small starburst companion NGC 2536. NGC 2535 has an ocular (eye-shaped) structure with two long tidal arms indicative of a recent, close, nonmerging encounter. Our observations rev...
Article
We made VLA HI observations of the young, interacting galaxy pair NGC 2535/36 in C and D Arrays (resolution = 12'' = 2.9 kpc). NGC 2535 has an "ocular" structure similar to that in IC 2163, which we studied previously. In NGC 2535, the intrinsic HI velocity dispersion is high, 30 km s(-1) over much of the disk, as compared to less than 10 km s(-1)...
Article
We use N-body simulations to study the non-linear evolution of spontaneous and tidally induced spiral patterns in galaxies on time-scales of several rotation periods of the disc. We find that the patterns can sometimes survive with an almost constant amplitude for five revolutions or more, and tend to be regenerated after disappearing temporarily....
Chapter
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Current research on the origin and evolution of active galaxies is comprehensively surveyed in this collaborative volume. Both of the proposed types of central activity - active galactic nuclei and starbursts - are analysed with a particular emphasis on their relationship to the large-scale properties of the host galaxy. The crucial question is wha...
Article
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Ten H I clouds with masses larger than 10 exp 8 solar masses in the interacting galaxies IC 2163/NGC 2207 are identified. Twenty-eight other interacting pairs of galaxies with large knots or star formation structures in their optical images are also tabulated. It is suggested that interactions can lead to the formation of greater than 10 solar mass...
Article
The present study of the nonaxisymmetric magnetic field present in M81 uses several mean-field dynamo models in disk geometry, and is mindful of the possibilities that M81 may have undergone a close encounter with a companion galaxy, and that the spiral structure may give a nonaxisymmetric structure to the disk turbulence, and therefore to the turb...
Article
We have modelled the tidal interaction between M 81 and NGC 3077, and found that the spiral arms of M 81 and the bridge of H I between M 81 and NGC 3077 can be the results of a close encounter between the two galaxies. A good fit to observations is found with a model where NGC 3077 moves in an approximately parabolic prograde orbit in the plane of...
Article
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An algorithm for star formation and gas heating is included in numerical simulations of galaxy disks. With a high disk mass and an inner Q-barrier, the simulations spontaneously generate and then maintain for several revolutions a long-lived two-arm spiral wave mode that resembles a grand design galaxy. Eventually a multiple arm pattern appears bec...
Article
Gerola et al. (1983) propose that isolated dwarf galaxies can form during galaxy interactions. As evidence of this process, Mirabel et al. (1991) find 10(exp 9) solar mass clouds and star formation complexes at the outer ends of the tidal arms in the Antennae and Superantennae galaxies. We describe observations of HI clouds with mass greater than 1...
Article
We discuss some aspects of the interrelationship between the dynamo problem for galaxies and their dynamics. First, we consider the generation of magnetic fields in the presence of fountain flows and galactic winds. Next, we discuss the distortion of a steady magnetic field by tidal effects and other transient spiral features. Finally, we give an e...
Conference Paper
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The galaxies NGC 2207 and IC2163 are undergoing a close tidal encounter that increased the HI velocity dispersion to 40 km/s and formed 10 giant HI clouds with masses in excess of 100 million solar masses each. Simulations of the interaction form a giant gas cloud with the mass of a dwarf galaxy in the outer part of a tidal arm, suggesting that tid...
Article
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We present calculations showing how both transient effects associated with nonaxisymmetric seed fields, and an interaction with a companion, can produce BSS type magnetic structure in a spiral galaxy.
Article
Recent H I observations of the M 81 group made with the Very Large Array (VLA) (Yun 1992; Yun et al. 1993) have revealed a previously unknown structure: a long 'bridge' of gas stretching from NGC 3077 towards the northwest. In a previous paper (Thomasson & Donner 1993), we presented a model of the tidal interaction between M 81 and NGC 3077, aimed...
Article
Full-text available
We discuss some aspects of the interrelationship between the dynamo problem for galaxies and their dynamics. First, we consider the generation of magnetic fields in the presence of fountain flows and galactic winds. Next, we discuss the distortion of a steady magnetic field by tidal effects and other transient spiral features. Finally, we give an e...
Article
We present calculations showing how both transient effects associated with nonaxisymmetric seed fields, and an interaction with a companion, can produce BSS type magnetic structure in a spiral galaxy.
Article
Full-text available
Galaxy interactions that agitate the interstellar medium by increasing the gas velocity dispersion and removing peripheral gas in tidal arms should lead to the formation and possible ejection of self-gravitationally bound cloud complexes with masses in excess of 10(8) Msun. Some of these complexes may eventually appear as independent dwarf galaxies...
Article
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N-body simulations are used to study the effect of spiral heating, viscous heating, and cooling by inelastic collisions on the molecular cloud ensemble velocity dispersion. The simulations include inelastic collisions between clouds as well as long-range gravitational forces. The theory for heating and cooling of the cloud population is described,...
Article
A long-lived two-armed spiral has been generated in an N-body computer simulation of a galaxy with a static bulge and halo and an active disk composed of 60,000 particles. The spiral lasts for about three pattern revolutions without severe distortion and persists for at least two more revolutions with distortions and bifurcations resulting from an...
Article
A long-lived two-armed spiral has been generated in an N-body computer simulation of a galaxy with a static bulge and halo and an active disk composed of 60,000 particles. The spiral lasts for about three pattern revolutions without severe distortion and persists for at least two more revolutions with distortions and bifurcations resulting from an...
Article
A companion can induce a variety of morphological changes in a galaxy. The author uses N-body simulations to study the effects of different kinds of perturbations on the dynamics of a disk galaxy. The model is two-dimensional, with a disk consisting of about 60,000 particles. Most of the particles (80%) represent the old stellar population with a h...
Article
The authors present an N-body simulation of an isolated galaxy with a long-lived two-armed spiral pattern. The galaxy consists of a static bulge and halo and a self-gravitating disk. The disk contains both gas clouds and an old stellar population. A two-armed spiral pattern develops in the initially featureless disk and lasts for several pattern re...
Chapter
Discs occur in a wide variety of astronomical contexts, ranging in size from planetary ring systems to galaxies. Because the dynamical problems posed by each type of disc are remarkably similar, the Astronomy Department of the University of Manchester decided to bring together experts in each area for a conference in December 1988. This book is a c...
Article
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We study, theoretically and withN-body simulations, the formation of spiral structures in retrograde galaxy encounters. A one-armed leading spiral dominates in a disc if (i) the tidal perturbation from the retrograde companion is large enough, and (ii) the disc is surrounded by a massive halo. From the literature we find that very few spirals in a...
Article
The authors study interactions between disc galaxies, in particular the case of a main system and a small perturber. Here they look at the behaviour using a responsive disturber in contrast to the more common approximation of a rigid mass distribution.
Article
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We study, theoretically and with N-body simulations, the formation of spiral patterns in retrograde galaxy encounters. A one-armed leading spiral dominates in a disk if the tidal perturbation from the companion is large and the disk is surrounded by a massive halo. Otherwise, a trailing pattern forms. The leading arm is made up of particles in slig...
Article
The cold component in a two-component N-body model of disk galaxies has previously been shown to heat up as the disk evolves. Here inelastic collisions between the "cold" particles, representing gas clouds, have been tried as a cooling mechanism, and found to work well. This model is then used to study both tidally perturbed and isolated galaxies....
Article
Full-text available
The tidal spiral arms in galaxies are studied using the two-dimensional polar coordinate N-body program of Miller (1976, 1978) and a two-component disk galaxy perturbed by a point-mass model. The density wave theory, which explains spiral arms in the presence of differential rotation, and the components of the model and computer program are discuss...

Citations

... The pair M51 -NGC 5195 is an archetypical system of this process, that has served also as a benchmarking model for numerical simulations of interacting galaxies, (Howard & Byrd 1990;Salo & Laurikainen 1993, 2000aDobbs et al. 2010;Querejeta et al. 2016); for more general examples of simulations of the influence of satellites on the disk structure see, e.g. (Sundelius et al. 1987;Hernquist 1987;Donner & Thomasson 1994;Huang & Carlberg 1997;Oh et al. 2008;Kazantzidis et al. 2009;Purcell et al. 2011;Struck et al. 2011;Widrow et al. 2014;Oh et al. 2015;D'Onghia et al. 2016). It has been conjectured that the presently observed spiral structure in our own Galaxy might have been dynamically excited by one or more companion flybys, (see e.g. ...
... The gravitational binding energy in a galaxy disk heats the stellar population during swing-amplified shear instabilities that make flocculent spiral arms (e.g., Fuchs & von Linden 1998). It can also heat the gas (Thomasson, Donner & Elmegreen 1991;Bertin & Lodato 2001;Gammie 2001) and feed turbulence (Huber & Pfenniger 2001;Wada, Meurer & Norman 2002). Continued collapse of the gas may feed more turbulence on smaller scales (Semelin et al. 1999, Chavanis 2002, Huber & Pfenniger 2002. ...
... This can be a viable explanation only because for galaxies the turbulent decay time might be slow enough, especially in their outer parts, if those fields are helical and non-kinematic Bhat et al., 2013). Moss et al. (1993) presented a model that incorporated a realistic representation of the so-called peculiar motions of M81 that were proposed to be the result of a recent close encounter with a companion galaxy. These peculiar motions are flows relative to the systematic differential rotation and have been obtained from an earlier stellar dynamics simulation by . ...
... Figure B.2: Colour inverted image of NGC 2535 obtained from http://www.skyserver.sdss.org/dr17/VisualTools/navi NGC 2535 is currently undergoing tidal interactions with NGC 2536 (Kaufman et al. (1997)). Similar to NGC 428, this also has a very prominent HI tidal stream. ...
... This scenario is supported by recurrent, short-lived transient spiral patterns (Sellwood, 2011). Notwithstanding, there are also N-body simulations that produce long-lived, quasi-steady patterns (e.g., Elmegreen and Thomasson, 1993;Zhang, 1996;D'Onghia et al., 2013;Saha and Elmegreen, 2016), some of which employing a large number of particles (Fujii et al., 2011). On the observational side, Martínez-García and González-Lópezlira (2013) analyzed a sample of normal or weakly barred galaxies and verified that at least 50% of the objects present azimuthal age/color gradients across spiral arms, which are signatures of long-lived spirals. ...
... Different methods are currently employed to simulate global evolution of collisionless point-mass systems of galaxies by N -body experiments. One algorithm for a simulation code that has found wide use was developed by Hohl and Hockney (1969), Hohl (1971Hohl ( , 1972, Miller (1971), Hockney and Brownrigg (1974), Quirk (1972), Athanassoula and Sellwood (1986), Combes et al. (1990), Pfenniger and Friedli (1993), Merritt and Sellwood (1994), Donner and Thomasson (1994), and others. The method samples the density field with a usually uniform grid. ...
... This further confirms an earlier claim by Sofue (1998), who described M82 as a low-mass galaxy with a strong central concentration of mass and hardly any evidence for a dark matter halo. The smallest of the three galaxies, NGC 3077, was found to have lost its gas during a close encounter with M81 (e.g., Brouillet et al. 1991;Thomasson & Donner 1993;Yun et al. 1993) and high resolution observations show that as much as 90% of the galaxy's atomic gas is situated in a prominent tidal arm (Walter et al. 2002a). ...
... It is well known now that the quasistationary hypothesis requires mechanisms to amplify the effect that maintains the waves (Mark 1976), since the tight winding waves experience rapid radial dispersion that propagates with the group velocity (Toomre 1969); these kinds of waves would be absorbed in the Lindblad resonances (Lynden-Bell & Kalnajs 1972). However, a feedback cycle produced by the Q-barrier reflecting a propagating wave might cause spiral modes to live longer (Bertin et al. 1989a(Bertin et al. , 1989bThomasson et al. 1990;Elmegreen & Thomasson 1993;Saha & Elmegreen 2016), but the wave is not steady (Sellwood 2011). ...
... The images shown in Fig. 1 belong to this set. We focused on manually deleting clumps embedded inside massive galaxies and on recovering galaxies that are either clearly disjoint from their neighbours or in tidal tails, to avoid rejecting tidally formed candidates 56 . We highlight that every galaxy lacking dark matter studied in this paper was recovered during this step. ...
... The spiral galaxies IC 2163 and NGC 2207 are involved in a grazing encounter (Elmegreen et al. 1995a(Elmegreen et al. , 1995bStruck et al. 2005). A prominent starburst region called Feature i by Elmegreen et al. (2000) lies in an outer arm of NGC 2207 on its anticompanion side. Feature i is the most luminous 8μm, 24μm, 70μm, Hα, and radio continuum source in NGC 2207/IC 2163 (Elmegreen et al. 2001(Elmegreen et al. , 2006Kaufman et al. 2012) and accounts for 23% of the total 24 μm emission from the galaxy pair (Elmegreen et al. 2006(Elmegreen et al. , 2016. ...