Caustic rings of dark matter

Sikivie, P.

doi:10.1016/s0370-2693(98)00595-4

Cited by 125 publications

(193 citation statements)

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“…Caustic rings are the more likely candidate for detection in an analysis of galactic rotation curves because they have the higher density contrast and because they are located closer to the galactic center, where the rotation curves are measured. Furthermore, a specific proposal [7] has been made for the radii a n of caustic rings: …”

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confidence: 99%

Evidence for universal structure in galactic halos

Kinney

Sikivie

2000

Phys. Rev. D

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The late infall of dark matter onto a galaxy produces structure (such as caustics) in the distribution of dark matter in the halo. We argue that such structure is likely to occur generically on length scales proportional to l ∼ t0vrot, where t0 is the age of the universe and vrot is the rotation velocity of the galaxy. A set of 32 extended galactic rotation curves is analyzed. For each curve, the radial coordinate is rescaled according to r →r ≡ r(v0/vrot), where we choose v0 = 220 km/s. A linear fit to each rescaled rotation curve is subtracted, and the residuals are binned and averaged. The sample shows significant features nearr = 40 kpc andr = 20 kpc. This is consistent with the predictions of the self-similar caustic ring model of galactic halos.PACS numbers: 95.35.+d, 98.35.GiThe rotation curves of most spiral galaxies are approximately flat, i.e. (v(r) constant) for r much larger than the disk radius [1], where v(r) is the circular velocity of gas at radial coordinate r. The flatness of galactic rotation curves implies that galaxies are surrounded by halos of dark matter, and that the halo density falls off approximately as ρ DM (r) ∝ 1/r 2 . The curves are far from exactly flat, however. They have all sorts of irregularities which may be referred to as "bumps". When a bump occurs at r >> disk radius, it indicates structure in the dark matter distribution, i.e. a deviation from a perfect ρ DM ∝ 1/r 2 law. We are motivated by the possibility that such structures have universality and that a statistical analysis of well measured extended rotation curves may reveal that.In refs. [2,3], 32 extended galactic rotation curves were selected and analyzed to test the validity of a modification of Newtonian dynamics (MOND) as an explanation of the "dark matter problem", i.e. the discrepancy between the flatness of galactic rotation curves and the exponential fall-off of galactic luminous matter distributions. We analyze the same set of rotation curves with a different goal, namely to search for structure within dark matter halos. We adopt the conventional wisdom that a rotation curve is a tracer of the galactic mass distribution according to the laws of Newtonian dynamics. However, the selection criteria used by the authors of refs. [2,3] that each rotation curve is an accurate tracer of the radial force law, and that it extends far beyond the edge of the luminous disk -are appropriate from the point of view of our analysis. We do not know of another data set of comparable quality. We use the complete data set described there, without any cuts of our own.One broad argument why structure may be present in galactic halos is that the halos form as a result of the infall of the dark matter surrounding the galaxy [4]. If the dark matter particles are collisionless, they oscillate back and forth numerous times before they are virialized by inhomogeneities in the galactic mass distribution [5].

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confidence: 99%

Evidence for universal structure in galactic halos

Kinney

Sikivie

2000

Phys. Rev. D

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“…The caustic rings are closed tubes whose cross-section is a D −4 catastrophe [5,6]. They are located near where the particles with the most angular momentum in a given inflow are at their distance of closest approach to the galactic center.…”

Section: Flow Equations At a Caustic Ringmentioning

confidence: 99%

“…Our estimates are for ǫ = 0.2 because they can most readily be obtained from Ref. [5] in that case. Combining Eqs.…”

Section: A Density Everywhere Except the Cuspsmentioning

confidence: 99%

“…Outer caustics occur where a given outflow reaches its furthest distance from the galactic center before falling back in. The inner caustics are rings [5,6]. They are located near where the particles with the most angular momentum in a given inflow reach their distance of closest approach to the galactic center before going back out.…”

Section: Introductionmentioning

confidence: 99%

“…The self-similar infall model of galactic halo formation predicts that the caustic ring radii [5] {a n : n = 1, 2, . .…”

Section: Introductionmentioning

confidence: 99%

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Gravitational lensing and structural stability of dark matter caustic rings

Onemli

2006

Phys. Rev. D

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Gravitational lensing by the dual cusp (A −3 ) catastrophes of the cold dark matter (CDM) caustic rings at cosmological distances may provide the tantalizing opportunity to detect CDM indirectly, and discriminate between axions and weakly interacting massive particles (WIMPs). The infall of CDM onto isolated galaxies such as our own produces discrete number of flows and caustics in the halo CDM distribution. Caustics are places where the CDM particles are naturally focussed. In the CDM cosmology, caustics in the distribution of dark matter are plentiful once density perturbations enter the nonlinear regime. Our focus is upon the caustic rings which are closed tubes whose cross-section is an elliptic umbilic (D −4 ) catastrophe with three dual cusps. We call this cross-section a "tricusp." Caustic rings are located near where the particles with the most angular momentum in a given inflow reach their distance of closest approach to the galactic center before going back out. We reparameterize the CDM flow near a caustic ring, and obtain the ring equations in space, as single valued functions of an angular variable parameterizing the tricusp. A caustic ring has a specific density profile, a specific geometry and, therefore, precisely calculable gravitational lensing signatures that vary on the caustic surface, depending on the location of the line of sight. We calculate the image magnification of point-like sources as a function of the angular parameter of the tricusp for the line of sights that are parallel to the galactic plane of the caustic ring and near tangent to the surface. The magnification monotonically increases 1 as the line of sight approaches to the cusps where it diverges in the limit of zero velocity dispersion. If the velocity dispersion is small but nonzero, the divergence is cut off, because the caustic surface gets smeared over some distance in space and the cusps are smoothed out. The lensing effects are no longer infinite at the cusps, but merely large. To estimate the magnification numerically, for the rings at cosmological distances and for the ring closest to us (the fifth caustic ring of the Milky Way), we choose sample points near the cusps. We find that the lensing effects are largest at the outer cusp which lies in (or, near) the galactic plane.Around the outer cusp, the surface is curved toward the side with two extra flows. We call such a surface concave. In the limit of zero velocity dispersion, at a sample point near the outer cusp, we find 37% magnification for the CDM caustic rings at cosmological distances. This is about 250 times stronger than the lensing effect we predicted for the concave folds (considering the A 2 catastrophes enveloping the galaxy), and 37 times stronger than the largest lensing effect we predicted for the CDM caustics (considering the convex folds of the rings) before. In the presence of finite velocity dispersion, the lower and upper bounds of the effective velocity dispersions of the axion and WIMP flows in galactic halos may be used to constrai...

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Dark Matter Caustics

Sikivie¹,

Kinney²

The Role of Neutrinos, Strings, Gravity, and Variable Cosmological Constant in Elementary Particle Physics

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Caustic rings of dark matter

Cited by 125 publications

References 13 publications

Evidence for universal structure in galactic halos

Evidence for universal structure in galactic halos

Gravitational lensing and structural stability of dark matter caustic rings

Dark Matter Caustics

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