The least action principle and the spin of galaxies in the Local Group

Dunn, A.; Laflamme, Raymond

doi:10.1093/mnras/264.4.865

Cited by 22 publications

(32 citation statements)

References 12 publications

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“…Even if the equations and the proper motion of M 31 given by Raychaudhury & Lynden-Bell (1989) are not fully correct (e.g. see Dunn & Laflamme 1993), the fundamental result still remains: the LG is not isolated and the proper motion of M 31 is not null.…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Introductionmentioning

confidence: 99%

“…Following the same methodology, Dunn & Laflamme (1993) independently derived the value for the proper motion of M 31 (µ l , µ b ) = (0.126, 0.0048) mas/yr. Despite this great improvement in the knowledge of the LG, new problems arose regarding its cosmological origins as noted by Governato et al (1997).…”

Section: Introductionmentioning

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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“…A dwarf galaxy in these closer samples, which experiences a far stronger direct interaction with the HG, does not respond significantly to the weaker external field acting on it. On the other hand, the collisionless description is suited to deal with the effects of distant galaxy groups (see the list in Table 1) and hence the influence of the external field on the other dwarf galaxies far away from a HG (see e.g., Raychaudhury & Lynden-Bell 1989;Peebles 1990;Dunn & Laflamme 1993;Peebles 1994).…”

Section: Causal or Casual?mentioning

confidence: 99%

Tidal effects on the spatial structure of the Local Group

Pasetto

Chiosi

2009

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Aims. The spatial distribution of galaxies in the Local Group (LG) is the footprint of its formation mechanism and the gravitational interactions among its members and the external massive galaxies or galaxy groups. Using a 3D-geometrical description of the spatial distribution of all the members of the LG (not only the satellites of the MW and M 31) based on present-day data of positions and distances, we found in our previous study that all galaxies (MW, M 31, their satellites, and even the most distant objects) are confined within a slab of about 200 kpc thickness. Examining how external galaxies or groups would gravitationally affect (and eventually alter) the planar structure (and its temporal evolution) of the LG, they found that the external force field acts parallel to the plane determined by geometry and studied this with the Least Action Principle. Methods. In this paper, we thoroughly investigated the role played by the tidal forces exerted by external galaxies or galaxy groups on the LG galaxies (the most distant dwarfs in particular) in shaping their large-scale distribution. We studied in particular an idea based on the well-known effect of tidal interactions, according to which a system of mass-points can undergo not only tidal stripping but also tidal compression and thus become flatter. Results. Excluding the dwarf galaxies tightly bound to the MW and M 31, the same tidal forces can account for the planar distribution of the remaining dwarf galaxies. We analytically recover our previous results and prove that a planar distribution of the LG dwarf galaxies is compatible with the external force field. We also highlight the physical cause of this result.

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“…Various strategies have been followed, ranging from a complete neglect of external forces (Peebles 1989), or taking account of the influence of merely a few nearby objects (Peebles 1989(Peebles , 1990Dunn & Laflamme 1993, towards methods involving approximate descriptions of external influences. The latter mostly incorporated the wider external influence through a frozen, linearly evolving, external tidal field estimated on the basis of the present-day locations of an extended sample of objects deemed representative for the external matter distribution (e.g.…”

Section: Cosmic Force Fields and Supercluster Dynamicsmentioning

confidence: 99%

“…For practical reasons, the original implementation had to be restricted to systems of at most a few dozen objects. Almost exclusively, the Local Group of galaxies formed the focus of these LAP studies (Peebles 1989(Peebles , 1990(Peebles , 1994Dunn & Laflamme 1993).…”

Section: Lap and External Forcesmentioning

confidence: 99%

Local supercluster dynamics: external tidal impact of the PSCzsample traced by optimized numerical least action method

Romano-Díaz¹,

Branchini²,

Weygaert³

2005

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Abstract. We assess the extent to which the flux-limited IRAS PSCz redshift survey encapsulates the complete or major share of matter inhomogeneities responsible for the external tidal forces affecting the peculiar velocity flow within the Local Supercluster and its immediate surroundings. We here investigate this issue on the basis of artificially constructed galaxy catalogs. Two large unconstrained N-body simulations of cosmic structure formation in two different cosmological scenarios form the basis of this study. From these N-body simulations a set of galaxy mock catalogs is selected. From these a variety of datasets is selected imitating the observational conditions of either the local volume-limited Local Supercluster mimicking NBG catalog or the deeper magnitude-limited PSCz catalog. The mildly nonlinear dynamics in the "mock" Local Supercluster and PSCz velocities are analyzed by means of the Least Action Principle technique in its highly optimized implementation of the Fast Action Method. By comparing the velocities in these reconstructions with the "true" velocities of the corresponding galaxy mock catalogs we assess the extent and nature of the external tidal influence on the Local Supercluster volume. We find that the dynamics in the inner 30 h −1 Mpc volume is strongly affected by the external forces. Most of the external forces can be traced back to a depth of no more than 100 h −1 Mpc. This is concluded from the fact that the FAM reconstructions of the 100 h −1 Mpc PSCz volume appear to have included most gravitational influences. In addition, we demonstrate that for all considered cosmological models the bulk flow and shear components of the tidal velocity field generated by the external distribution of PSCz galaxies provides sufficient information for representing the full external tidal force field.

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The least action principle and the spin of galaxies in the Local Group

Cited by 22 publications

References 12 publications

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

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

Tidal effects on the spatial structure of the Local Group

Local supercluster dynamics: external tidal impact of the PSCzsample traced by optimized numerical least action method

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