Lopsided spiral galaxies

Jog, Chanda J.; Combes, F.

doi:10.1016/j.physrep.2008.12.002

Cited by 111 publications

(137 citation statements)

References 183 publications

(344 reference statements)

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“…The significantly larger shift found for M 99 appears to conflict with the collisional simulations, but the concomitance of the inner density flatness with the halo shift in M 99 is an observational support to the simulations. A dynamical mechanism that motivates a disturbed DM halo, and maybe a misalignment with luminous matter, could be a tidal event (Jog & Combes 2009;van Eymeren et al 2011). A tidal interaction between M 99 and a massive companion has actually occurred in the past Gyr, maybe 750 Myr ago (Duc & Bournaud 2008).…”

Section: A Shifted Dark Matter Halo In M 99?mentioning

confidence: 99%

“…However, a tidal scenario only seems problematic to explain the amplitude of the v 02 asymmetry in the innermost regions. Such a scenario is expected to enhance the strength of lopsidedness with radius (e.g., Jog & Combes 2009), while a roughly constant kinematical asymmetry is measured within R ∼ 7 kpc. A mechanism other than a tidal event thus remains to be proposed for the origin of the innermost lopsidedness of the total mass distribution of M 99, including that of the dark matter component.…”

Section: A Shifted Dark Matter Halo In M 99?mentioning

confidence: 99%

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Asymmetric mass models of disk galaxies

Chemin

Huré

Soubiran

et al. 2016

A&A

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Mass models of galactic disks traditionally rely on axisymmetric density and rotation curves, paradoxically acting as if their most remarkable asymmetric features, such as lopsidedness or spiral arms, were not important. In this article, we relax the axisymmetry approximation and introduce a methodology that derives 3D gravitational potentials of disk-like objects and robustly estimates the impacts of asymmetries on circular velocities in the disk midplane. Mass distribution models can then be directly fitted to asymmetric line-of-sight velocity fields. Applied to the grand-design spiral M 99, the new strategy shows that circular velocities are highly nonuniform, particularly in the inner disk of the galaxy, as a natural response to the perturbed gravitational potential of luminous matter. A cuspy inner density profile of dark matter is found in M 99, in the usual case where luminous and dark matter share the same center. The impact of the velocity nonuniformity is to make the inner profile less steep, although the density remains cuspy. On another hand, a model where the halo is core dominated and shifted by 2.2−2.5 kpc from the luminous mass center is more appropriate to explain most of the kinematical lopsidedness evidenced in the velocity field of M 99. However, the gravitational potential of luminous baryons is not asymmetric enough to explain the kinematical lopsidedness of the innermost regions, irrespective of the density shape of dark matter. This discrepancy points out the necessity of an additional dynamical process in these regions: possibly a lopsided distribution of dark matter.

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Section: A Shifted Dark Matter Halo In M 99?mentioning

confidence: 99%

Section: A Shifted Dark Matter Halo In M 99?mentioning

confidence: 99%

Asymmetric mass models of disk galaxies

Chemin

Huré

Soubiran

et al. 2016

A&A

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“…1. Although it is possible to explain the small-scale lopsideness by internal mechanisms only (e.g., Jog & Combes 2009), the external ring's off-centering suggests a galaxy collision.…”

Section: Co Line Morphologiesmentioning

confidence: 99%

Molecular gas in NUclei of GAlaxies (NUGA)

Combes

Baker²,

Schinnerer³

et al. 2009

A&A

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We present high-resolution maps of the CO(1-0) and CO(2-1) emission from the LINER 2 galaxy NGC 1961. This galaxy is unusual among late-type (Sc) disk galaxies in having a very large radial extent and inferred dynamical mass. We propose a head-on collision scenario to explain the perturbed morphology of this galaxy -both the off-centered rings and the inflated radius. This scenario is supported by the detection of a steep velocity gradient in the CO(1-0) map at the position of a southwest peak in radio continuum and near-infrared emission. This peak would represent the remnant of the disrupting companion. We use numerical models to demonstrate the plausibility of the scenario. While ram pressure stripping could in principle be important for shocking the atomic gas and produce the striking head-tail morphology, the non detection of this small galaxy group in X-ray emission suggests that any hot intragroup medium has too low a density. A prediction of the collision model is the propagation of ring waves from the center to the outer parts, superposed on a probable pre-existing m = 2 barred spiral feature, accounting for the observed complex structure of rings and spokes. This lopsided wave accounts for the sharp boundary observed in the atomic gas on the southern side. Through dynamical friction, the collision finishes quickly in a minor merger, the best fit being for a companion with a mass ratio 1:4. We argue that NGC 1961 has a strongly warped disk, which gives the false impression of a nearly face-on system; the main disk is actually more edge-on, and this error in the true inclination has led to the surprisingly high dynamical mass for a morphologically late-type galaxy. In addition, the outwardly propagating ring artificially enlarges the disk. The collision de-stabilizes the inner disk and can provide gas inflow to the active nucleus.

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“…Indeed, more than a third of the spiral galaxies host large-scale lopsided asymmetry (Richter & Sancisi 1994;Rix & Zaritsky 1995;Bournaud et al 2005;Zaritsky et al 2013), see Jog & Combes (2009), for a discussion of the threshold of lopsidedness. Some of the mechanisms that are shown to generate lopsidedness in the outer galaxy are: cooperation of orbital streams to a lopsided pattern (Earn & Lynden-Bell 1996); response of an axisymmetric disc to a lopsided dark halo (Jog 1997(Jog , 1999; satellite infall onto a galaxy (Zaritsky & Rix 1997); a tidal encounter (Bournaud et al 2005;Mapelli et al 2008); asymmetric gas accretion (Bournaud et al 2005) or through internal disc instabilities (Saha et al 2007;Dury et al 2008).…”

Section: Introductionmentioning

confidence: 99%

Angular momentum transport and evolution of lopsided galaxies

Saha¹,

Jog²

2014

Monthly Notices of the Royal Astronomical Society

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The surface brightness distribution in the majority of stellar galactic discs falls off exponentially. Often what lies beyond such a stellar disc is the neutral hydrogen gas whose distribution also follows a nearly exponential profile at least for a number of nearby disc galaxies. Both the stars and gas are commonly known to host lopsided asymmetry especially in the outer parts of a galaxy. The role of such asymmetry in the dynamical evolution of a galaxy has not been explored so far.Following Lindblad's original idea of kinematic density waves, we show that the outer part of an exponential disc is ideally suitable for hosting lopsided asymmetry. Further, we compute the transport of angular momentum in the combined stars and gas disc embedded in a dark matter halo. We show that in a pure star and gas disc, there is a transition point where the free precession frequency of a lopsided mode, Ω − κ, changes from retrograde to prograde and this in turn reverses the direction of angular momentum flow in the disc leading to an unphysical behaviour. We show that this problem is overcome in the presence of a dark matter halo, which sets the angular momentum flow outwards as required for disc evolution, provided the lopsidedness is leading in nature. This, plus the well-known angular momentum transport in the inner parts due to spiral arms, can facilitate an inflow of gas from outside perhaps through the cosmic filaments.

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Lopsided spiral galaxies

Cited by 111 publications

References 183 publications

Asymmetric mass models of disk galaxies

Asymmetric mass models of disk galaxies

Molecular gas in NUclei of GAlaxies (NUGA)

Angular momentum transport and evolution of lopsided galaxies

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