The least-action method, cold dark matter, and omega

Dunn, A.; Laflamme, Raymond

doi:10.1086/187821

Cited by 22 publications

(41 citation statements)

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“…It would be more accurate, however, to consider the objects as representing the dark matter halos of galaxies (which as far as is known interact only through gravity). The point-mass approximation provides a reasonable simulation of gravitational e †ects, since multipole moments decay rapidly with distance (Dunn & LaÑamme 1995 found them to be quite unimportant), and in any case the conclusions of this study are not a †ected by the detailed form of the gravitational potential used.…”

Section: Introductionmentioning

confidence: 64%

The Least‐Action Principle: Theory of Cosmological Solutions and the Radial Velocity Action

Whiting

2000

ApJ

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Formulating the equations of motion for cosmological bodies (such as galaxies) in an integral, rather than di †erential, form has several advantages. Using an integral, the mathematical instability at early times is avoided, and the boundary conditions of the integral correspond closely with available data. Here it is shown that such a least-action calculation for a number of bodies interacting through gravity has a Ðnite number of solutions, possibly only one. Characteristics of the di †erent possible solutions are explored. The results are extended to cover the motion of a continuous Ñuid. We give a method for generalizing an action so as to use velocities, instead of positions, in boundary conditions, which reduces in particular cases to those given by Giavalisco et al. and Schmoldt & Saha. The velocity boundary condition is shown to have no e †ect on the number of solutions.

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Section: Introductionmentioning

confidence: 64%

The Least‐Action Principle: Theory of Cosmological Solutions and the Radial Velocity Action

Whiting

2000

ApJ

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“…The problem has long been debated with controversial results (White et al 1988;Davis & Peebles 1983;Natarajan & Springel 2004;Dunn & Laflamme 1995).…”

Section: Limitations and Assumptionsmentioning

confidence: 99%

Planar distribution of the galaxies in the Local Group: a statistical and dynamical analysis

Pasetto

Chiosi

2006

A&A

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Aims. Basing on the projected distribution of the galaxies in the Local Group, Sawa & Fujimoto found that they all seem to distribute on a rather thin plane containing the two mayor local galaxies of the Local Group, Milky Way and Andromeda, and all their dwarf satellites. As their conclusion could be severely biased by projectional distortion effects, we re-analyse the whole issue using a different approach. In brief, adopting known data on positions and distances, we make use of the analytical geometry and look for the plane that minimizes the distances of all galaxies to it. A planar distribution is indeed found that, however, does not coincide with the plane found by Sawa & Fujimoto. Why? The second part of this study is devoted to answer this question and to find a dynamical justification for the planar distribution. Methods. To this aim, we apply the Hamilton Method (Minimum Action) to investigate the dynamics of the two major system of the Local Group, Milky Way and Andromeda, under the action of external forces exerted by nearby galaxies or groups external to the Local Group. Results. We find that the planar distribution is fully compatible with the minimum action and that the external force field is likely parallel to the plane. It pulls the galaxies of the Local Group without altering their planar distribution. Special care is paid to evaluate the robustness of this result. Conclusions. In this paper we have examined the spatial distribution of galaxies in the Local Group. They are confined to a plane that can be statistically and dynamically understood as the result of the Minimum Action. The planar distribution seems to be stable for a large fraction of the Hubble time. The external force field, that has likely been constant over the same time interval, does not alter the planar distribution as it is nearly parallel to it. Effects due to undetected halos of sole Dark Matter are briefly discussed. They could be a point of uncertainty of the present study.Key words. stellar dynamics -Local Group -galaxies: dwarf IntroductionRecent reviews of the state-of-art of our understanding of the structure, past history, galaxy content, and stellar populations in individual galaxies of the Local Group (LG) are by van den Bergh (1999), Mateo (1998) andGrebel (2001). However, our present knowledge of the proper motions of Andromeda (M 31) and most galaxies of the LG is dramatically insufficient and inadequate to correctly reconstruct the past and present structure of the LG. As a matter of facts, no orbital parameters can be derived with adequate precision to constrain the space of velocities for all known objects. As a consequence of it, the dynamical evolution of the LG galaxies, and the dynamical origin of the dwarf satellites orbiting around and interacting with the two major galaxies, i.e. Milky Way (MW) and M 31, are not clear.Over the years, many authors addressed these issues both observationally and theoretically, with the aim of understanding the evolution of the LG galaxies. Since the first obser...

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“…However, it seems that the dominant members of the IC 342/Maffei Group may be massive enough and near enough to the Local Group to have had an influence on its dynamical history (McCall 1989;Valtonen et al 1993), thereby calling into question the binary hypothesis of LG timing. Peebles (1990) and Dunn & Laflamme (1995) extended this approach by tracing the orbits of the LG galaxies back in time, under the "least action principle". These analyses rely heavily on having a full census of LG galaxies and on accurate distances to them.…”

Section: Dynamics Of the Local Groupmentioning

confidence: 99%

The Universe behind the Milky Way

Kraan-Korteweg

Lahav

2000

Astronomy and Astrophysics Review

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Abstract. Due to the foreground extinction of the Milky Way, galaxies appear increasingly fainter the closer they lie to the Galactic Equator, creating a "zone of avoidance" of about 25% in the distribution of optically visible galaxies. A "whole-sky" map of galaxies is essential, however, for understanding the dynamics in our local Universe, in particular the peculiar velocity of the Local Group with respect to the Cosmic Microwave Background and velocity flow fields such as in the Great Attractor region.Various dynamically important structures behind the Milky Way have only recently been made "visible" through dedicated deep surveys at various wavelengths. The wide range of observational searches (optical, near infrared, far infrared, radio and X-ray) for galaxies in the Zone of Avoidance are reviewed, including a discussion on the limitations and selection effects of these partly complementary approaches. The uncovered and suspected large-scale structures are summarized. Reconstruction methods of the density field in the Zone of Avoidance are described and the resulting predictions compared with observational evidence. The comparison between reconstructed density fields and the observed galaxy distribution allow derivations of the density and biasing parameters Ω 0 and b.

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The least-action method, cold dark matter, and omega

Cited by 22 publications

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The Least‐Action Principle: Theory of Cosmological Solutions and the Radial Velocity Action

The Least‐Action Principle: Theory of Cosmological Solutions and the Radial Velocity Action

Planar distribution of the galaxies in the Local Group: a statistical and dynamical analysis

The Universe behind the Milky Way

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