Rings and shells of "dark matter" as MOND artifacts

Abstract

MOND predicts that a mass, M, contained within its transition radius r_t=(MG/a0)^{1/2}, may exhibit a feature at about that radius in the form of a shell, or projected ring, in the deduced distribution of its phantom dark matter. This occurs despite the absence of any underlying feature in the true (``baryon'') source distribution itself. The phenomenon is similar to the appearance of an event horizon and other unusual physics ``in the middle of nothing'' near the transition radius of General Relativity $MG/c^2$. We consider the possibility that this pure MOND phenomenon is in the basis of the recent finding of such a ring in the galaxy cluster Cl 0024+17 by Jee et al. We find that the parameters of the observed ring can be naturally explained in this way; this feature may therefore turn out to be a direct evidence for MOND. We study this phenomenon in simple, axisymmetric configurations aligned with the line of sight: spherical masses, a dumbbell of spherical masses, and an elongated, thin structure. The properties of the apparent ring: its radius, surface density, and contrast, depend on the form of the MOND interpolating function and on the exact three dimensional distribution of the sources (the thin-lens approximation is quite invalid in MOND). We also comment on the possible appearance of orphan features, marking the Newtonian-to-MOND transition, in high surface brightness galaxies. In particular, we find that previously unexplained structure in the rotation curves of some galaxies may be evidence for such features.

29 pages, 9 figures, Astrophysical J., in press; changed to match published version; added a discussion of the rotation curve of NGC 2841 with new MOND interpolating functions

References in corpus (7)

• On the Proof of Dark Matter, the Law of Gravity and the Mass of Neutrinos
• Discovery of a Ringlike Dark Matter Structure in the Core of the Galaxy Cluster Cl 0024+17
• The modified Newtonian dynamics-MOND-and its implications for new physics
• Confrontation of MOND with the rotation curves of early-type disc galaxies
• Insight into the baryon-gravity relation in galaxies
• Neutrinos as cluster dark matter
• XMM-Newton study of the lensing cluster of galaxies CL0024+17

Cited by in corpus (2)

• X-ray Group and cluster mass profiles in MOND: Unexplained mass on the group scale
• MOND and the lensing Fundamental Plane: No need for dark matter on galaxy scales